CLINICAL STEPS
IN FIXED PROSTHODONTICS
Introduction
Dental prosthetics is an extremely vast and complex specialty. Perhaps that's
why it is studied over the course of four semesters during dental school. What every
student should understand is that the concepts studied serve as the foundation for
future clinical reasoning, which is essential in the practice of dentistry.
Another particularly important aspect is the importance of interdisciplinarity and
collaboration that must exist among all clinical specialties so that the therapeutic
decision and the medical act itself are most appropriate for each patient. The last few
decades have revolutionized all branches of dental prosthetics. The emergence of new
technologies, new equipment, and new concepts has made it possible to carry out more
predictable, precise, and efficient treatments.
Fixed dental prosthetics are extensively covered by international experts in
various books and treaties. This course is a concise and up-to-date version of the most
important clinical aspects of fixed prosthodontics, structured into 9 distinct chapters. The
ultimate goal is for the student to use these concepts to understand how to examine a
patient, analyze all the data for the purpose of making a correct diagnosis, and then
decide on an appropriate treatment plan for each patient. This includes performing fixed
prosthetic treatment steps according to standardized protocols.
The authors of this course dedicated to students have tried to contribute
personally regarding iconography and those small but incredibly important tips and
tricks that help novice practitioners perfect their clinical skills.
Prof. Dr. Anca Jivănescu
CHAPTER 1. EXAMINATION, DIAGNOSIS, AND TREATMENT PLAN FOR FIXED
PROSTHETIC RESTORATIONS
The clinical examination phase is extremely important in establishing a fixed prosthetic
restorative treatment. It begins with taking the patient's history, which is recommended
to be done in a different environment than the consultation room.
The questionnaire primarily aims to determine whether the patient is a candidate for
fixed prosthetic restorative treatment and whether they desire to change the design of
their smile. The time allocated for the examination phase is usually directly proportional
to the difficulty of the patient's aesthetic or functional issues. It is very useful for the
patient to complete a questionnaire while waiting, which can help clarify these issues.
Smile Self-Assessment Questionnaire? (according to RE Goldstein, Change your smile)
| Question
| 1. Are you confident in your smile?
| 2. Do you prefer to be photographed only from a certain
|
side of your face?
| 3. Do you believe someone in your circle has a nicer
|
smile than yours?
| 4. Do you browse through magazines and wish you had a
|
smile like a model?
| 5. When you look through magazines, does the smile
|
catch your attention first?
| 6. When you look in the mirror, do you see any flaws in
|
your teeth or gums?
| 7. Would you like your teeth to be whiter?
| 8. Are you satisfied with the way your gums look?
| 9. Do you feel that too many or too few teeth are
|
prominent when you smile?
Yes No
| 10. Do you feel that your gums are not prominent enough when you
smile?
| 11. Are your teeth too long or too short?
| 12. Are your teeth too wide or too narrow?
| 13. Are your teeth too straight or too round?
| 14. Are you satisfied with the way your teeth are aligned?
The patient's response should not be suggested by the doctor
. If the patient answers "no" to every question except questions No. 1, 8, and 14, it
means they are satisfied with their smile.
Aesthetic evaluation begins with observing facial elements. Even if the teeth
appear attractive individually, if they do not harmonize with other facial structures, the
overall impression will not be aesthetic. To achieve aesthetic restoration, the dentist
must understand the shape, texture, and color of natural teeth and how these teeth
relate to other facial structures. This information must then be conveyed to the dental
laboratory to create the desired restoration.
The examination will be done from the frontal and sagittal views. Facial symmetry
and the proportionality of facial planes will be examined, which are attributes of an
attractive face. If perceptible abnormalities such as skeletal asymmetries are present,
interdisciplinary consultation (orthodontist, maxillofacial surgeon) will be sought.
In most cases, there is a reduction in the lower facial height due to dental wear or
disturbances in the eruption of posterior teeth. Restoring the vertical dimension of
occlusion will often lead to a substantial improvement in facial appearance.
One of the simplest methods to evaluate facial aesthetics in relation to the
vertical dimension of occlusion is to observe the patient from the front with the lips at
rest and the mandible in a relaxed position. In the case of patients without skeletal
asymmetries or dento-facial anomalies, this position generates optimal facial beauty. If
closing into maximum intercuspation results in a decrease in aesthetic appearance, it
indicates an incorrect occlusal vertical dimension, i.e., too small.
Ideally, when the patient closes from the rest position to maximum intercuspation,
there should be a minor change in facial appearance.
In most cases, patients fall into one of these two situations: excessive vertical
overclosure of teeth with a reduced occlusal vertical dimension, or a reduced occlusal
vertical dimension due to excessive tooth wear.
The next step is to evaluate the patient sagittal. In cases of Angle Class I
relationship, the facial plane is slightly convex, the vertical line connects the glabella
with the pogonion, and the subnasale point is in the middle of the distance between
them.
Facial profiles with excessively convex or concave appearances cannot be
modified solely through dental restorations. If the patient insists on changing their facial
appearance, cephalometric analysis will be required to confirm the skeletal diagnosis.
In cases where patients have moderate to excessive dental wear, the facial
profile conforms to Angle Class III occlusion, which is due to the forward and upward
rotation of the mandible as the teeth wear down.
Evaluating the sagittal position of the lips will provide information about skeletal and
dental relationships. The nasolabial angle in Caucasians is 90-100 degrees for men and
95-105 degrees for women.
Dental restorations, by positioning the teeth more vestibular or oral, may have a
relatively small effect on lip position. The position of the upper lip is most influenced by
the maxillary bone and the cervical third of the incisors. Major changes in lip position
can only be achieved through orthodontic or orthognathic treatment. Plastic surgery is
used to enhance lip contour and reduce the nasolabial angle. The lower edge of the
nose can create an aesthetic problem, resulting in an abnormal nasolabial angle. If
changing the nasolabial angle is necessary for aesthetic reasons, plastic surgery is
required.
The relationship between the nose, lips, and chin can be evaluated using one of
the three reference lines (Ricketts, Steiner, Burstone), serving as a guide for the lower
third of the profile. (Fig.1.1)
Fig.1.1. Examining the profile highlights the nasolabial
angle and the E-Rickets plane.
If the maxilla is prominent, the nasolabial angle is below 90 degrees, and the
profile is convex. In these situations, consideration will be given to creating smaller, less
dominant restorations in the frontal area. If the maxilla is retruded, the nasolabial angle
is above 90 degrees, the profile is concave, and restorations placed more vestibular and
prominent can be crafted.
The relationship of the lips with these lines can help formulate the diagnosis and
treatment plan regarding the position of the anterior teeth and the alveolus. Using these
lines will demonstrate whether the lip is anterior or posterior to the ideal position,
providing indications for the positioning of the teeth and alveolus. Lips situated anterior
to the reference lines necessitate a more posterior placement of the teeth and alveolus.
Lips situated posterior to these lines require anterior traction of the maxilla or mandible.
This should be done after cephalometric analysis and interpretation by a specialist.
Aesthetic modifications of lip position and the lower facial height can be achieved
through surgical, orthodontic, or prosthetic treatment.
The next step in aesthetic analysis is assessing the relationship between the lips
and teeth, i.e., the visibility of the teeth, both statically and dynamically. In a 30-year-old
woman, the degree of tooth visibility at rest is approximately 3.5mm.
Prosthodontists recommend that the visibility of the front teeth at rest should be
approximately 2mm. Between 2 and 4 mm is the visibility range that achieves maximum
aesthetic effect for a woman.
The size and position of the teeth, the length and mobility of the lips affect the
disposition of the teeth, both statically and dynamically. The average length of the
maxillary central incisor measures between 10-11mm. The average length of the lip is
20-22mm measured from the base of the nose to the upper lip edge. The mobility of the
lip in a normal smile is approximately 7-8mm. When a person smiles, the tip of the
maxillary canine comes very close to or touches the lower lip, while the maxillary
incisors are positioned approximately 2-4mm from the lower lip. This position is
influenced by the curvature of the lower lip and the incisal plane.
All anterior teeth are displayed in a smile, and often the first and second premolars, and
sometimes even the molars.
If the patient exhibits inadequate or excessive visibility of the teeth during a
smile, then these three parameters, namely static and dynamic lip position and lip
length, are critical factors during treatment. If the patient shows more than 4mm of the
maxillary central incisors in repose and the teeth need to be lengthened, this will be
achieved by elongating the incisal edge. If the degree of tooth visibility is 3-4mm and it
is found that the teeth are too short, then surgical crown lengthening is necessary.
If the degree of tooth visibility at rest is insufficient but the length of the incisors
and the mobility of the lips are normal, and the teeth are not adequately displayed
during a smile, this indicates insufficient vertical dimension of occlusion (VDO). In this
situation, it is not desirable to elongate the crowns of the teeth, but rather, the occlusion
must be evaluated and VDO needs to be corrected.
If excessive display of the upper incisors is observed at rest, with normal lip
mobility and lip length, and more than 3mm of the gingival margin is visible during a
smile, orthognathic surgical treatment is indicated.
In clinical situations where the degree of tooth visibility at rest is normal, tooth
length is within normal limits, but there are discrepancies in terms of the smile line and
the degree of tooth visibility, it is not recommended to perform restorative treatments
that compromise their structural integrity. If there is a moderate or severe distortion of
the smile line, orthodontic treatment is preferred.
In an aesthetic smile, there is what is called negative space, which is a reduced
space between the posterior maxillary teeth and the buccal mucosa. If the space
appears excessive during a smile, it can be corrected by slightly increasing the
vestibular contour of the posterior teeth, especially when prosthetic restorative
treatment is necessary. If the negative space is too small due to an exaggerated
convexity of the vestibular surface of the posterior teeth, the effect will be inaesthetic.
Ideally, the dental midline (interincisal line) should overlap with the facial midline.
This doesn't always happen, but it has been observed that deviations from normal in the
dental midline do not have a significant effect on dentofacial aesthetics if the two lines
are parallel.
If the deviation of the interincisal line from the facial midline is less than 4mm and
parallel to the facial midline, it may not be perceived as inaesthetic by others. Dental
midlines can be corrected through orthodontic or restorative treatment.
Regarding the proportions of the maxillary teeth, many authors recommend using
the golden proportion to define their optimal width as they move away from the midline.
The maxillary central incisors should be relatively symmetrical and generally dominate
the smile but not excessively.
Recent studies in the literature have shown that measurements of contemporary
individuals' anterior teeth do not always adhere strictly to the golden proportion. The
relationship between the central incisor and lateral incisor is closer to the golden
proportion in an aesthetic smile. The optimal width of the lateral incisor is 62%-65% of
that of the central incisor. The canine does not follow the golden proportion rule and is
approximately 75% of the optimal width of the maxillary lateral incisor.
The positions of the front teeth can vary, with one lateral incisor typically more
rotated than the other, one may be more palatalized, etc., and canines are generally in
different vertical positions and angled differently.
Establishing the correct gingival relationship with the lips and teeth is essential in
an aesthetic composition. The gingival line (free gingival margin), gingival color, and
gingival papilla contour should be evaluated separately.
To achieve an aesthetic effect, the gingival line of the anterior teeth should be
relatively parallel to the horizon and relatively symmetrical on both sides of the midline.
It is not critical for the gingival line of the lateral incisor to be lower than that of the
central incisor if it is not noticeable when the person smiles. The gingival contour in the
vestibular area should have a scalloped appearance.
To systematize this data, it is useful to complete a facial aesthetics assessment
form.
Facial Aesthetics Assessment Form
1. Facial Analysis
A. Broad Smile
1. Position of the interpupillary line relative to the occlusal plane: parallel / deviated
to the right / deviated to the left
2. Relationship of the interincisal line to the facial midline: symmetrical / deviated to
the right / deviated to the left
3. Lip relationship to the midline: symmetrical / deviated to the right / deviated to the
left
B. Lips at Rest
1. Upper lip thickness: thick / medium / thin
2. Lower lip thickness: thick / medium / thin
3. Lip position: prominent / retruded
4. Degree of tooth visibility at rest
5. Upper: _______ mm
6. Lower: _______ mm
C. Profile
1. Nasolabial angle: normal approximately 90° / maxillary prognathism < 90° / maxillary
retrognathism > 90°
2. Ricketts' E-plane (from nose to chin): upper lip 4 mm from the E-plane / lower lip 2 mm
from the E-plane / within normal limits / convex / concave
4. Dental Analysis
A. Proportion of central incisors (measured with a caliper)
• Width-to-length ratio (W:L) > 80% (ideal: L=80% of W:L) / < 80%
B. Proportion between central incisor, lateral incisor, and canine (golden
rule: 1.6:1:0.6)
•
Central incisor width: _______ mm
•
Lateral incisor width: _______ mm
•
Canine width: _______ mm
C. Axial inclination (draw on the diagram the degree of inclination)
•
Gingival characteristics and dental height (draw on the
diagram)
•
Mucogingival problems / Gingival asymmetry
5.
Diagnostic Information
After examination and evaluation, you can proceed to complete an aesthetic
assessment table to summarize the main aesthetic issues and requirements.
Aesthetic evaluation table (circle the correct answer and fill in the columns).
Aesthetic Issue
| Yes | No
---------------------------------------|-------|------1. Gingival Height Asymmetry
Location:
|
|
|
|
---------------------------------------|-------|------2. Black Triangles
Location:
|
|
| Yes | No
---------------------------------------|-------|------3. Gingival Color Changes
Location:
|
|
| Yes | No
---------------------------------------|-------|------4. Over contoured Crowns
Location:
|
|
| Yes | No
---------------------------------------|-------|------5. Poor Marginal Adaptation
Location:
|
|
| Yes | No
---------------------------------------|-------|------6. Acute Periodontal Conditions
Location:
|
| Yes | No
---------------------------------------|-------|-------
|
7. Tooth Mobility or Furcation
Involvement
|
|
| Yes | No
Location:
|
|
---------------------------------------|-------|------8. Endodontic Lesions
|
Location:
|
| Yes | No
---------------------------------------|-------|------9. Occlusion: Incisal Wear,
|
Wear Facets
Location:
|
| Yes | No
|
|
---------------------------------------|-------|------10. Continuous Canine-to-Distal
|
Progression (Curve Overlap)
Location:
|
|
| Yes | No
|
---------------------------------------|-------|------11. Presence of Tremors
Location:
|
|
| Yes | No
---------------------------------------|-------|------12. Presence of Diastema
Size:
|
|
| Yes | No
---------------------------------------|-------|------13. Dental Crowding
Location:
|
|
| Yes | No
---------------------------------------|-------|------14. Cracked or Fractured Teeth
Location:
|
|
| Yes | No
---------------------------------------|-------|------15. Discolored Teeth
Location:
|
|
| Yes | No
---------------------------------------|-------|------16. Surface Texture
|
|
Smooth
| Yes | No
Moderate
|
Rough
|
|
|
---------------------------------------|-------|-------
Detailed clinical examination should be supplemented with photographic examination,
mainly focusing on detailing the three aspects:
•
Facial composition;
•
Dento-labial composition (lips, gums, and teeth);
•
Dental composition (teeth and gums).
Fig. 1.2. Facial Composition
Fig. 1.3. Dento-Labial Composition (Lips, Gums, Teeth)
Fig. 1.4. Dental Composition (Teeth and Gums)
Once the basic assessment has been completed, the dentist has the necessary
information to establish a general diagnosis. Answering the five basic questions makes
the diagnostic process straightforward. Diagnosis always begins with an analysis of the
patient's face. If the gingival positioning is incorrect or the smile is asymmetric, then the
treatment plan becomes interdisciplinary, and the five basic questions help determine
the aetiology of the discrepancies.
Question 1: What are the facial proportions and skeletal relationships?
For a proportional (balanced) appearance of the face, the dimensions of the
middle and lower thirds should be 1:1. If the lower third of the face is larger compared to
the middle third, the general diagnosis will be excessive vertical maxillary (EMV). This
patient exposes a significant portion of the gingiva both in the anterior and posterior
areas. This condition is related to the growth and development of the maxilla and
mandible. The mandibular ramus is usually short, resulting in an obtuse angle with the
mandibular plane. The maxilla grows excessively so that the maxillary teeth occlude
with the mandibular teeth. If EMV leads to significant functional and/or aesthetic
problems, the primary treatment is orthognathic surgery.
This involves a Le Fort I
osteotomy followed by immobilization of the maxilla. In some cases, the mandible will
naturally rotate into a favourable occlusal position with the maxilla. If the mandible does
not find a correct occlusal position, bilateral sagittal mandibular osteotomy will be
performed. Overly large maxillae and those with width discrepancies can be treated with
multiple osteotomies. If the patient chooses not to undergo orthognathic surgery, Botox
treatment (Allergan) can be used to mask excessive gingival exposure.
If the lower third of the face is shorter than the middle third, this is usually due to
insufficient vertical development of the maxilla. In cases where insufficient maxillary
development leads to significant functional and/or aesthetic problems, the primary
treatment is again orthognathic surgery. This procedure typically involves maxillary
osteotomy and bilateral sagittal mandibular osteotomy.
Finally, the anterior-posterior relationship between the maxilla and mandible
should be evaluated. Ricketts' aesthetic line (E-line) is a useful tool for assessing this
relationship. In a sagittal view, a line is drawn from the nose to the chin. In a 1:1
representation of a young face, the upper lip should be 2 to 4 mm behind the line, and
the lower lip should be 0 to 2 mm behind the line. A normal facial profile is straight. If the
lower lip is more than 2 mm behind the line, the facial profile is convex, indicating a
Class II Angle malocclusion. If the lower lip surpasses the line, the facial profile is
concave, indicating a Class III Angle malocclusion.
Question 2: What are the length and mobility of the upper lip?
Upper Lip Length
The average length of the upper lip in young women (25-30 years) is 20 to 22
mm, and in young men, it's 22 to 24 mm. Age is important because as the patient ages,
the upper lip tends to lengthen. Typically, the upper lip will lengthen by 1 mm per decade
starting at the age of 40. If the upper lip is shorter than normal, a significant portion of
the gingiva will be exposed during a wide smile. Surgical procedures can lower the
upper lip, but these interventions are not routine. By modifying labial behaviour, the
patient can reduce the mobility of the upper lip. They are instructed to look in a mirror
and learn to smile in a way that exposes as little gingiva as possible. This is an effective
procedure if the patient practices the exercise in front of a mirror and works only for the
rehearsed smile, not for emotional smiles. The primary treatment for a short upper lip is
Botox. It is injected into the elevator muscles of the upper lip, temporarily paralyzing
these muscles. In some circumstances, dermal injection can be used for the treatment
of a short upper lip.
Lip mobility
Normal mobility of the upper lip, measured from rest to a wide smile, is 6 to 8
mm. Ideal mobility moves the upper lip toward the gingival line (a line drawn from
canine to canine at the gingival level) in a wide smile. A hypermobile upper lip can move
well above the gingival line, exposing a significant portion of the gingiva. Although not
specifically related to sex or age, women tend to have greater lip mobility. When a
hypermobile upper lip is encountered, it is often related to a longer upper lip, and the
treatment options are limited. The patient should be aware that the upper lip is longer
than normal and will continue to lengthen with age due to collagen loss and decreased
muscle tone. A rarely used treatment is shortening the lip with plastic surgery, indicated
only if the issue is a major aesthetic disadvantage for the patient. On the other hand,
lengthening the incisal margins of the maxillary anterior teeth can be performed to make
them more visible both at rest and in a wide smile. However, this can lead to significant
over-dimensioning of the incisal margins from the canine to the first premolar. To correct
excessive upper lip length, extensive coronal reshaping dental procedures are needed.
Once the basic evaluation has been conducted, the dentist has the necessary
information to obtain a general diagnosis. Getting answers to the five basic questions
makes the diagnostic process straightforward. Diagnosis always begins with analysing
the patient's face. If the positioning of the gums is incorrect or the smile is asymmetric,
then the treatment plan becomes interdisciplinary, and the five basic questions help
determine the aetiology.
Hyperactive Upper Lip:
The normal mobility of the upper lip, measured from rest to a wide smile, is 6 to 8
mm. Ideal mobility moves the upper lip towards the gingival line (a line drawn from canine
to canine at the gingival level) during a wide smile. A hypermobile upper lip can move well
beyond the gingival line, exposing a significant portion of the gum. Although not
specifically related to gender or age, women tend to have greater lip mobility. When
increased lip mobility is combined with anatomically shorter lips, increased gum exposure
is more common, particularly in women compared to men. Botox injections, lip behaviour
education, and plastic surgery can be helpful in this case. The hypertrophied nasal
septum depressor muscles are sectioned, resulting in reduced lip mobility at the midline.
However, this procedure does not address other facial muscles that can continue to cause
significant lip mobility.
Hypomobile Upper Lip:
Reducing lip mobility can negatively affect smile dynamics. There are two different
types of hypoactive smiles. First, the patient does not want or know how to smile normally.
The patient may adopt a hypoactive smile to cover up an aesthetic deficit. Treating this
deficiency creates the possibility of developing a more dynamic smile. If the patient does
not know how to smile normally, lip muscle tonicity exercises should be performed to
increase lip mobility. In the second type of hypoactive smile, the patient cannot smile too
much. Often, the upper lip elevator muscles are limited due to the strong activation of the
upper lip depressor muscles. If the depressor muscles are treated with Botox, the elevator
muscles can increase upper lip mobility.
Question 3: What is the relationship between the gingival line and the horizontal
plane?
When positioned correctly, maxillary anterior teeth exhibit symmetry with the
gingival line. This is a line drawn from the gingival margin of a canine to the gingival
margin of the contralateral canine. The central incisors should be in line, and the lateral
incisors can be in line or up to 1.5 mm below the line, and this line should be parallel to
the horizontal plane. Posterior teeth should maintain the same horizontal symmetry.
When teeth erupt excessively/continuously, with alveolar process, a gingival line that is
no longer straight but becomes straight and concave appears. It occurs more frequently
in the anterior teeth, but it can occur anywhere in the oral cavity, involving a variable
number of teeth. Continuous eruption generally occurs in three cases:
1. Continuous tooth eruption due to improper occlusal contact (Class II Angle
malocclusion) or lack of antagonists.
2. Continuous tooth eruption due to attrition.
3. Occlusal plane modification due to excessive eruption or attrition. As teeth erupt,
the dentogingival complex moves with them, resulting in an inaesthetic gingival
line.
There are three primary treatment strategies for this situation. The first and generally
most desirable treatment is orthodontic intrusion of the teeth to their initial position. If
continuous eruption occurred due to a lack of occlusal contact, the teeth may not require
coronal restoration after intrusion. However, long-term retention of intruded teeth needs
attention. This can be achieved by either establishing a new occlusal relationship with the
presence of antagonists or by using a fixed or removable retention appliance. If extrusion
occurred due to attrition, teeth would require coronal restorations at the completion of
orthodontic treatment. A more traditional but generally less desirable treatment in a patient
with dental wear is surgical crown lengthening and reestablishment of the initial gingival
line position before restoration. There are several disadvantages to this treatment. Firstly,
the surgical intervention will expose root surfaces, resulting in a less favourable surface
for adhesive restorations. Secondly, due to the narrower root diameter, definitive
restorations will have a triangular shape, which is less aesthetic. Thirdly, surgical
intervention results in gingival margins with a more bulging appearance rather than a
knife-edge appearance. The gingival margin should terminate on enamel, but when
moved onto root surfaces, it will not heal in a knife-edge fashion. Lastly, surgical crown
lengthening requires the removal of interproximal alveolar bone, typically resulting in open
gingival embrasures. Ultimately, osteotomy will lead to an increased crown-to-root ratio.
The third treatment option is to increase the vertical dimension of occlusion through
orthodontic treatment or coronal restorations. This procedure does not directly treat
excessive dental eruption. However, it provides interocclusal space for coronal
restorations in patients with secondary attrition-related excessive dental eruption.
Question 4: What is the length of the maxillary central incisor?
When the maxillary central incisor is shorter than average (10-11 mm), there are
three compatible aetiologies:
1. Microdontia
2. Loss of incisal length due to attrition
3. Pathological passive eruption
If the aetiology is microdontia, the teeth will be proportionally smaller, and the enamelcement junction may be located in the sulcus. If the aetiology is the loss of incisal length
due to attrition, the normal anatomy will be altered. If the aetiology is pathological passive
eruption, the diagnosis should be made based on the response to question #5.
Question 5: Is the enamel-cement junction palpable in the gingival sulcus?
If the measured tooth is short, and the enamel-cement junction cannot be determined
with a probe within the sulcus, the aetiology is pathological passive eruption. The gingival
tissue has not migrated to its correct position, 1 to 2 mm from the enamel-cement junction,
leading to excessive enamel coverage. The normal process of passive eruption is
completed by the age of 15-16. Pathological passive eruption is surgically treated through
crown lengthening surgery.
Classification of Partial Edentulism
In the case of partial edentulism, the prosthodontic diagnosis should take into
account a universally accepted classification system. The most important classifications
are:
1. Kennedy Classification
2.ACP Classification (American College of Prosthodontics)
The Kennedy Classification comprises 4 classes:
1. Class I: Bilateral edentulous areas.
2. Class II: Unilateral edentulous areas.
3. Class III: Edentulous areas with teeth remaining both anterior (mesial) and
posterior (distal).
4. Class IV: Edentulous areas in the anterior region on both sides of the midline.
Applegate established some rules for applying the Kennedy Classification:
•
Non-recoverable teeth with extraction indications are not considered for
classification (they are considered missing teeth).
•
Absent teeth that will not be prosthetically replaced are not considered for
classification. This situation usually pertains to third molars or second molars
without antagonists.
•
The most posterior (distal) edentulous space determines the class of edentulism.
•
Any additional edentulous space is termed as modification.
•
The extent and/or location of modifications are not specified.
•
Class IV does not present modifications
ACP Classification of Partial Edentulism
(American College of Prosthodontists)
Within this classification, there are 4 diagnostic criteria:
1. Extent and topography of edentulous spaces
2. Condition of abutment teeth
3. Occlusal relationships
4. Edentulous ridges
Each diagnostic criterion can be categorized into four classes:
•
Class I: Ideal or Minimal Impairment
•
Class II:Moderate involvement
•
Class III: Substantial involvement
•
Class IV: Severe involvement
Criterion 1 – Extent and Topography of Edentulous Spaces
Class 1 - Ideal or Minimally Affected Arches by Edentulism
Single edentulous space located in a single arch that meets one of the following
conditions:
•
Any maxillary frontal edentulous space that does not exceed 2 incisors
•
Any mandibular frontal edentulous space that does not exceed 4 incisors
•
Any maxillary or mandibular lateral edentulous space that does not exceed 2
premolars or one premolar and one molar
Class 2 - Moderately Affected Arches by Edentulism
Edentulous spaces present in both arches and meet one of the following conditions:
•
Any maxillary frontal edentulous space that does not exceed 2 incisors
•
Any mandibular frontal edentulous space that does not exceed 4 incisors
•
Any maxillary or mandibular lateral edentulous space that does not exceed 2
premolars or one premolar and one molar
•
Absence of a maxillary or mandibular canine
Class 3 - Substantially Affected Arches by Edentulism
•
Any maxillary or mandibular lateral edentulous space involving more than 3 teeth
or including 2 molars
•
Any anterior or posterior edentulous space involving more than 3 teeth
Class 4 - Severely Affected Arches by Edentulism
•
Any edentulous space or combination of edentulous spaces requiring increased
therapeutic compliance from the patient.
Criterion 2 – Condition of Abutment Teeth
Class 1 - Ideal or Minimally Affected Abutment Teeth:
•
No preparatory treatment is required
Class 2 - Moderately Affected Abutment Teeth:
•
Insufficient dental structures to support intracoronal restorations in 1-2 sextants
•
Abutment teeth require limited preparatory treatment (periodontal, endodontic,
orthodontic, etc.) in 1-2 sextants
Class 3 - Substantially Affected Abutment Teeth:
•
Insufficient dental structures to support intra-coronal restorations in 3 sextants
•
Abutment teeth require limited pre-prosthetic treatment (periodontal, endodontic,
orthodontic, etc.) in 3 sextants.
Class 4 - Severely Affected Abutment Teeth:
•
Insufficient dental structures to support intra-coronal restorations in 4-6 sextants
•
Abutment teeth require limited preparatory treatment (periodontal, endodontic,
orthodontic, etc.) in 4-6 sextants
•
Abutment teeth with a reserved prognosis.
Criterion 3 – Occlusal Relationships
Class 1 - Ideal or Minimally Affected Occlusal Relationships:
•
No occlusal preparatory treatment is required
•
Inter-arch and intermaxillary relationships of Class I
Class 2 - Moderately Affected Occlusal Relationships:
•
Limited occlusal preparatory treatment is required, such as selective occlusal
interference removal through grinding
•
Inter-arch and intermaxillary relationships of Class I
Class 3 - Substantially Affected Occlusal Relationships:
•
Reconstruction of the occlusal scheme without altering the vertical dimension of
occlusion
•
Inter-arch and intermaxillary relationships of Class II
Class 4 - Severely Affected Occlusal Relationships:
•
Reconstruction of the occlusal scheme, altering the vertical dimension of occlusion
•
Inter-arch and intermaxillary relationships of Class II division 2 or Class III.
Criterion 4 – Edentulous Ridges
For partially edentulous cases, the classification of edentulous ridges is made according
to the criteria for complete edentulism.
The table below systematically presents the classes and diagnostic criteria for partial
edentulism according to the American College of Prosthodontists (ACP).
Class
I
II
III
IV
Alveolar process bone height
At least 21 mm
X
16-20 mm
X
11-15mm
X
Up to 10 mm
X
Maxillary Edentulous Ridge Morphology
Type A - Resists vertical and horizontal displacement,
X
pterygomaxillary groove without torus
Type B - Reduced lateral vestibular height, erased
X
pterygomaxillary groove, no torus interfering with the distal
border of the prosthesis
Type C - Reduced frontal vestibular height, minimal support,
X
resilient frontal ridge
Type D - Reduced frontal and lateral vestibular height,
X
posterior torus, frontal hyperplasia
Mandibular Muscle Insertions
Type A - Corresponding fixed mucosa
X
Type B - No fixed mucosa in the frontal area, mentalis
X
muscle
Type C - No fixed mucosa in the frontal area, mentalis
X
muscle, genioglossus muscle
Type D - Fixed mucosa only on the lingual side
X
Type E - No fixed mucosa
X
Mandibulo-Maxillary Relationships
Class I
X
X
X
X
Class II
X
X
Class III
X
X
Need for Pre-prosthetic Surgical Interventions
Minor interventions on soft tissues
X
Minor interventions on hard tissues
X
Simple implants
X
Implants with augmentation
X
Correction of dentofacial malformations
X
Hard tissue augmentation
X
Extensive soft tissue remodelling
X
Reduced Inter-arch Space
18-20 mm
X
Surgical correction required
X
Tongue Anatomy
Hypertrophy (occupies interdental space)
X
Hyperactivity - with posterior position
X
Aggravating Factors (Modifiers)
Oral manifestations of systemic conditions
Mild
Moderate
X
X
Severe
X
Psychosocial Factors
Moderate
X
Major
Cranio-Mandibular Disorders
X
X
Paraesthesia / Dysesthesia
X
Maxillofacial Defects
X
Ataxia
X
Refractory Patients
X
Once the general diagnosis has been established, an interdisciplinary treatment strategy
can be developed. Determining the regional diagnosis (pulp status, periodontal condition,
TMJ status, etc.) contributes to the development of the definitive sequential treatment
plan.
Bibliografy:
1. Winston W.L. Chee, BDS Dent Clin N Am 48 (2004).
2. R.Goldstein. Change your smile. 2012.
3. Dorin Bratu, Robert Nussbaum. Bazele clinice si tehnice ale protezarii fixe.
4. McGarry TJ, Nimmo A, Skiba JF, Ahlstrom RH, Smith CR., Koumjian JH.
Classification sistem for partial edentulism. J Prosthodont 2002.
5. Irfan Ahmad. Prosthodontics at a glance, Wyley 2015.
6. Robbins, Rousse. Global Diagnosis. Quintessence 2016.
CHAPTER 2. COMMUNICATION METHODS
DOCTOR-PATIENT-DENTAL TECHNICIAN
The success of a prosthetic restorative treatment that fulfils optimal aesthetic and
functional desires is based on a thorough examination and effective communication
between the doctor and the patient, as well as between the doctor and the dental
technician.
Most dentists diagnose aesthetic problems using traditional means of radiography
and clinical examination. The therapeutic decision is based on each doctor's own vision
and experience. Clinicians' concepts of facial aesthetics may or may not coincide with
patients' perceptions and desires. This is where most communication problems often
begin.
First and foremost, a therapeutic strategy, a systematic approach to aesthetic
problems, must be mentally developed. This means identifying the problem and
visualizing the therapeutic solution, together with the patient and the dental technician.
Identifying problems requires a systematic analysis in three stages of the patient's
aesthetic needs:
•
Aesthetic evaluation form;
•
Computerized simulation;
•
Diagnostic models and wax-up.
Through visual explanations, images, photographs, and models, the risk of
misunderstanding within the team of specialists (doctor-technician) or between the doctor
and the patient is minimized.
The most common classical means of visualization and communication are:
•
Study models;
•
Diagnostic wax or composite resin modelling;
•
Use of markers (outlining on the model or in the oral cavity);
•
Direct testing modelling in the oral cavity (with wax or composite resins);
•
Photographs of other patients with similar problems and their resolution methods.
Unfortunately, these methods are often inadequate for helping the patient understand
how a treatment or restoration will change their appearance or facial features.
Most patients know very little about the potential of dental aesthetics, especially
the limitations of aesthetic restorative treatments. Therefore, they sometimes have
unrealistic expectations, which, if not clarified from the beginning, can lead to
disillusionment, failures, and dissatisfied patients.
The more efficient the communication with the patient, the greater the chances of
successfully completing the treatment and satisfying the patient.
Traditional doctor-patient communication methods have several advantages but
also some disadvantages. Therefore, the most appropriate method should be selected
based on the clinical situation.
2.1. STUDY MODELS
Study models are the most common and frequently used means of communication
with the patient, as well as with the dental technician. These allow the doctor to develop
the treatment plan and analyse possible therapeutic alternatives. Unfortunately, these
models have limited possibilities for demonstrating to the patient what is intended to be
achieved with specialized treatment. In the absence of the color of natural teeth and
surrounding tissues (lips, gingival tissues), the teeth in study models can hardly fit into a
final image of dentofacial aesthetics. Often, patients cannot imagine what can be
achieved in the end by just observing these monochromatic models. (Fig. 2.1.)
Fig. 2.1. Rarely can patients visualize treatment results on study models.
2.2. DIAGNOSTIC MODELING ON STUDY MODELS (WAX-UP TECHNIQUE)
Modifications performed on study models involve the sectioning or repositioning of
crowded or spaced teeth, with or without the addition of wax, to simulate the expected
treatment results. Wax-up diagnostic model represents a precise method for measuring
and assessing tooth proportions. Although it efficiently facilitates communication between
the dentist and the dental laboratory, diagnostic model entails additional costs, especially
in terms of time. Moreover, it often cannot convincingly visualize for the patient the goals
of aesthetic treatment.
On the study model, wax or resin will be added to conform to certain facets (Fig.
2.2). These can subsequently be tested in the patient's oral cavity and serve as a useful
guide when elongating clinical crowns or altering the shape and position of teeth.
If mutually agreed upon by the dentist and the patient, they can be used as a model
for the final restorations.
Fig. 2.2. Because wax or resin diagnostic models come in different colors (green,
yellow, blue), patients may have difficulty visualizing treatment results.
2.3. SIMULATION OF CORONAL CONTOURS USING IN-MOUTH MARKERS
Alcohol-soluble markers provide a simple and cost-effective way to highlight
minor changes in tooth shape. By using a black marker on the dry tooth surface, the
areas that need to be removed can be outlined. When the patient looks into a mirror
from a distance of 30cm, can visualize the effects of cosmetic contouring, as the black
color of the marker matches the background of the oral cavity behind the teeth. This
technique can easily simulate the removal of dental tissues and cosmetic reshaping but
cannot highlight other treatments such as whitening or veneers.
Fig. 2.3.a. Initial situation. b. Using a black marker to simulate necessary coronal
reshaping. In this case, simple subtractive reshaping is insufficient, so diagnostic
model(diagnostic cast) is required.
2.4. PHOTOS OF PATIENTS WITH SIMILAR ISSUES
A common and effective way to present therapeutic solutions is by creating
albums with photos of other patients who have had various dental aesthetic issues and
how they were resolved. These albums can be made available to the patient in the
waiting room, serving as an educational and informative tool. Through the photos in the
albums, we can showcase the therapeutic options available and actively involve the
patient in the treatment plan.
These photos of other patients are impersonal and can only be considered a starting
point that can enhance the patient's understanding of aesthetic treatments. However, for
the patient, it may be challenging to imagine how their aesthetic appearance will change
with the planned treatment just by looking at pictures of other patients with similar
issues.
Fig. 2.4. Photos of other patients with similar situations can be suggestive for visualizing
therapeutic possibilities: a. Initial situation; b. Final smile.
2.5. DIRECT IN-MOUTH TESTING MODELS (MOCK-UP TECHNIQUE)
If contour changes to the teeth are required through addition, they can be done directly
in the patient's oral cavity using tooth-colored wax or composite resin. These are
molded directly onto the tooth surface, and this technique is called mock-up. The
technique is quite time consuming and cannot be used when orthodontic or periodontal
surgery is required.
Fig. 2.5. By modelling with white wax or composite resin directly on the tooth surface,
certain coronal reshaping can be simulated.
There are several basic rules for diagnostic cast based on specific aesthetic principles:
•
Start with the central incisors, which are considered dominant teeth (the
width/height ratio is 80%). Provide the technician with information about the
tooth's length as determined during the aesthetic analysis.
•
Aim for symmetry with respect to the midline.
•
Apply the golden proportion principle for correct tooth modelling.
•
Apply the principle of distal axial inclination direction.
•
Incisal embrasures should progressively increase in size from incisors to
premolars.
•
Model angular lines parallel to the long axis of the teeth.
•
Model incisal contour and texture according to age and gender.
•
Ensure the correct positioning of gingival height and gingival zenith.
2.6. TESTING PROVISIONAL RESTORATIONS
For patients seeking a highly customized outcome in aesthetic restorative treatment,
more detailed visualization methods are required. One such method involves creating a
conformer using the thermo-vacuum forming technique, made from transparent foil over
a study model. Resins matching the tooth or gingival tissue color are applied to this
conformer to simulate the desired changes. This so-called diagnostic prosthesis can
produce a realistic effect of the intended modifications, both in terms of color, shape,
and tooth position.
In cases of patients with protruding front teeth, this method is contraindicated, as it will
exacerbate the malposition and have the opposite effect to the desired one. This
technique is even more time consuming than diagnostic wax modelling. It is
recommended only for very demanding and difficult patients who want to know the
exact aesthetic final result. Naturally, these patients will incur additional charges.
In more challenging situations involving radical changes to smile design, it is advisable
to create a provisional test restoration. This allows for effective communication with both
the patient and the dental laboratory. With this method, the patient can directly visualize
changes in tooth shape and size and participate in potential adjustments through
suggestions. Through these provisional restorations, the patient does not need to rely
on imagination ("how will the restoration look?") but can see the modification of the
smile design directly in the oral cavity.
In addition to aesthetics, phonetics (fricative and sibilant sounds) can be checked, and,
in the end, comfort and the impact on the patient's psyche are evaluated. It is
recommended that until the patient accepts the provisional restoration, the definitive
restoration should not be initiated. Once the provisional restorations are accepted, they
will be duplicated in the laboratory and serve as a guide for creating the final
restorations.
Below is a case of a patient who requested replacement of an unsatisfactory fixed
prosthesis in the frontal zone (Fig.2.6). After diagnostic wax modelling and the creation
of a putty silicon key (Fig.2.7), the provisional restoration was fabricated (Fig.2.8). Only
after the patient expressed satisfaction with the shape and arrangement of the teeth did
we proceed with the definitive restoration (Fig.2.9).
Fig.2.6. Patient requiring a change in smile design.
Fig.2.7. Provisional test restoration.
Fig. 2.8. Temporary Test Restoration in the Oral Cavity
Fig. 2.9. Definitive Restoration a. on the Model and b. in the Oral Cavity
2.8. OTHER MEANS OF COMMUNICATION WITH THE LABORATORY
Most often, to facilitate communication and visualize the effects of aesthetic
treatments, two or three of the mentioned methods are combined. In the case of
patients with multiple aesthetic issues, such as diastema in the maxillary teeth,
crowding of the mandibular front teeth, and the need for coronal contouring, multiple
visualization and communication methods are necessary. In these situations, both
diagnostic wax modelling or resin modelling for closing diastemas and modelling for
coronal contouring of the lower front teeth are needed, and finally, marking new
demarcation lines (e.g., shortening some teeth, shifting proximal lines). Certainly, all
these methods require a lot of time and skill on the part of the dentist.
Often, the dental laboratory is not immediately adjacent to the dental office, and
the dental technician is not always available. Therefore, it is necessary to transmit
explicit data related to the patient and what is desired as the outcome of aesthetic
restorative treatment. The most common means of communication with the dental
laboratory are:
•
Digital photography
•
Modified shade guides
•
Lip impression
2.8.1. DIGITAL PHOTOGRAPHY
The popularity of digital photography in the field of dentistry has increased in
recent years. This method offers several advantages and benefits in our profession. It is
relatively easy to use, with the dentist requiring basic knowledge of photographic
techniques and computer use to maximize its potential. Currently, it cannot be said that
the digital photography method is standardized. Digital cameras interpret color
differently, making standardization difficult. Factors such as lighting, the angle at which
the photo is taken, and environmental factors will alter color perception. It is essential to
use digital photography as an adjunct to other techniques and take several serial photos
using proper lighting to provide as much necessary color analysis information as
possible.
To use the information provided by digital photography effectively, several factors
should be considered. Firstly, it is advisable to use different backgrounds (usually a
neutral gray background) and take photos from different angles. Vectorization involves
taking photos from different angles to visualize interproximal areas of enamel
unsupported by dentin without the yellowish-red reflection of proximal teeth. It has been
found that an angle of 67-70 degrees with the buccal surface of the tooth is best for
highlighting hue and saturation. For brightness, a 90-degree angle should be used.
Through digital photography, various facial parameters can be communicated,
such as facial shape, profile, lip tone, relationships with the gingival margin, incisal
length, translucency degree, or other characteristics.
To capture tooth shape and color more accurately, it is recommended to use
higher zoom levels, holding the teeth from the shade guide close to the respective tooth.
Fig.2.10. With the help of digital photography, the dentist can convey certain color,
translucency, and texture characteristics.
For surface shape and gloss, the teeth should be cleaned and dried; then,
images should be captured perpendicular to the tooth surface. A dark-colored
background should be used to increase contrast. It is quite challenging to distinguish
whether a tooth has low gloss, is dehydrated, or has undergone a bleaching process,
but this issue can be clarified through anamnesis.
When lenses are positioned perpendicular to the tooth surface, light can reflect to
the camera like a mirror. Using a polarized light filter will cancel out the reflected light,
making color determination easier. Brightness can be more easily appreciated in blackand-white photos. Images should be captured at a 1:1 ratio to capture surface
characteristics.
For accurate color recording, it is desirable to use a dual (bilateral) flash with
color correction. The optimal settings for DSLR digital cameras are as follows: F-Stop =
28-32; manual settings; shutter speed = 1/25-1/250; ISO = 100-200, manual focus.
Fig. 2.11. Digital camera with dual
bilateral flash.
To highlight the degree of translucency, photos should be overexposed, a black
background should be used, and photos should be taken at a 60-degree angle. To
observe the degree of opalescence through photos, certain conditions must be met; this
will allow for precise measurement of enamel thickness for future ceramic restorations.
A dark background will reduce reflection, which is accentuated by the flash. Red
color reflections come from soft tissues, pass through the enamel, mix with the blue
ones, greatly reducing the opalescence effect. If a black background is used, the
contrast between the blue opalescence of the enamel and the red-yellow underlying
dentin is increased. Exposure variations are called bracketing and can be done in
several ways, most commonly by adjusting the aperture. Closing the aperture allows
less light to pass to the digital sensors.
For a photograph to be as useful as possible in transmitting color, it is recommended to
use different backgrounds, angles, and apertures.
Surface texture and gloss can have a significant effect on the final restoration's
appearance. If these characteristics are not accurately replicated, many restorations will
not have a natural appearance, even if the color is suitable. The smoother the tooth
surface (and more reflective), the brighter it appears. To counteract this issue, some
cameras use filters to eliminate surface gloss. Systems that do not use such filters
record overly high brightness values, which can have undesirable effects on the
aesthetics of the future restoration.
2.8.2. MODIFIED SHADE GUIDES
Natural teeth do not have a uniform color, making it challenging to find a perfectly
matching shade in existing shade guides. In cases where an appropriate color cannot
be found in the shade guides, modified shade guides are used. A tooth with higher
brightness (V) and lower saturation (C) values is selected from the shade guide. On this
sample, prepared with a bur to create a rough surface, surface colors are applied to
modify the color, making it as similar as possible to the natural tooth. This sample is
sent to the laboratory and serves as a perfect guide for selecting the color of the future
restoration. This method is useful, especially when a highly individualized restoration is
desired with various special effects, such as mimicking fissures, proximal discolorations,
decalcification white spots, etc., or in the case of covering a single incisor that must
harmonize perfectly with its counterpart. (Fig.2.12.a,b).
F
Fig. 2.12. a. Pigments are applied to the tooth's surface on the shade guide to transfer
all surface characteristics to the laboratory. b. Selecting the color with the modified tooth
from the shade guide.
No matter how accurate an impression is, it is not possible to reproduce the
surface texture precisely on plaster models. Even high-quality photographic images do
not provide conclusive information about the texture and gloss of natural teeth. To
provide the technician with the most precise information regarding these characteristics,
teeth from denture sets with gloss and texture as similar as possible to natural teeth can
be selected and sent to the laboratory. These will serve as a guide for the future
restoration.
2.1.9.3. LIP IMPRESSION AND FACIAL MASK
In an aesthetic treatment plan, obtaining a lip model can be very useful. Lip
impression is usually done with standard materials, typically irreversible hydrocolloids.
The lip model, or the so-called facial mask, represents a three-dimensional model that is
applied directly to the models mounted in the articulator. These models will serve as a
guide for the technician to evaluate and modify the smile line, occlusal plane, oral
corridor, tooth and gingival display mode.
One of the most well-known systems for lip impression and facial mask creation
is the Kalco system from Zhermack, which includes special impression spoons,
impression material (alginate), and silicon used to create the facial mask. After lip
impression with the impression spoon and irreversible hydrocolloid, the facial mask is
created, which is applied to the models mounted in the articulator. This will be an
important guide for the technician in creating the fixed prosthesis.
Fig.2.13. Impression spoons (Kalco system). Fig.2.14. Lip impression with alginate.
Fig. 2.15. Lip impression after removal from the oral cavity.
Fig. 2.16. Facial Mask on the Articulator
Fig. 2.17. Achieving prosthetic restoration and testing in the articulator with a facial
mask.
Lip impression is essential when aiming for a change in the position of the upper
front teeth. With its help, a diagnostic cast can be achieved in a more realistic position.
In cases of immediate complete denture placement, the model obtained through
lip impression can be used to achieve a more natural arrangement of teeth in the
prosthesis, as it provides valuable information regarding the smile line, position of the
lower lip, buccal corridor, and midline.
The conventional means and methods described in this chapter are accessible to
any practitioner, but they often require a significant amount of time and may not always
yield conclusive results.
Virtual simulation (Digital Smile Design)
Computerized imaging represents a modern, more sophisticated, yet much faster and
efficient alternative for patient evaluation and communication.
Dentists can currently take advantage of the benefits offered by the integration of digital
technologies into the routine of dental laboratories, such as the so-called virtual or
digital wax-up and digital surgical guides.
To encourage patient involvement and active participation in the treatment plan
development, it's advisable to perform computerized simulations right in front of the
patient. Certain modifications, such as teeth whitening, cosmetic contouring, or tooth
replacement, can be done quickly, in a matter of minutes, right in front of the patient.
However, there are certain situations that require a more careful study of captured
images, and in many cases, it's beneficial for the dentist to perform the simulation in the
absence of the patient (14).
There are indeed several virtual smile design systems available, ranging from the
classic Digital Smile Design (DSD) introduced by Christian Coachman to those
associated with CAD/CAM systems (e.g., Cerec Smile Design, Romexis Smile Design,
Medit Smile Design).
CHAPTER 3. PREPROSTHETIC TREATMENT
Edentulism refers to the absence of one or more dental units, which can vary in
terms of location, frequency, or extent. Depending on the location, size, and duration of
the edentulous space, disturbances can occur in all functions of the stomatognathic
system, including mastication, phonation, and aesthetic function.
Following the loss of a tooth over time, a series of changes occur. These
changes lead to the atrophy of the alveolar ridge in the affected area, migration of
adjacent teeth towards the edentulous space, the development of parafunctional muscle
activity resulting in the formation of wear facets. Depending on the body's ability to
adapt to the new situation, temporomandibular joint dysfunction may develop
consequently (1).
The migration of adjacent teeth towards the edentulous space can occur
horizontally due to the available space and lack of support, thus disrupting the position
of teeth within the arch. This tilting of adjacent teeth creates additional areas for food
retention, which are difficult to clean. The change in the axis of the teeth results in a
non-physiological distribution of occlusal forces, which were originally aligned with the
long axis of the tooth until the edentulous space and tooth tilting occurred (Fig. 1, 2).
The action of the force arm, which shifts eccentrically from the long axis of the tooth
during tilting, combined with food retention and the negative impact of food impaction,
can lead to the development of periodontal lesions such as periodontal pockets. Over
time, these pockets can lead to the loss of adjacent teeth to the edentulous space.
Additionally, there is a disturbance in the balance of the opposing dental arch, where the
tooth opposing the edentulous space begins to migrate vertically. This vertical
movement can be of two types:
-
Egression, where the tooth moves vertically, bringing the alveolar bone along
with it.
-
Extrusion, where the tooth migrates vertically while the alveolar bone remains in
its original position.
When dental extrusion begins, if timely intervention is not carried out, it can lead
to the exposure of the root portion of the tooth. This results in dental sensitivity because
the cementum layer covering the tooth's root is porous and lacks the ability to isolate the
enamel from the aggressive factors in the oral cavity. The porous structure of root
cementum significantly increases susceptibility to dental caries.
Fig. 3.1. Migration of teeth in the horizontal and vertical planes.
Fig. 3.2. The loss of the canine resulted in the tilting, mesialization, and vertical
migration of the upper premolar.
In these two types of vertical migration of antagonistic teeth in the edentulous gap, if
timely intervention is not carried out, they can continue until they encounter the
edentulous ridge and may cause ulcerative lesions that accentuate vertical bone loss in
the edentulous ridge. Furthermore, the vertical migration of antagonistic teeth in the
edentulous gap can disrupt mandibular propulsion movements, blocking this type of
movement.
Any treatment plan and any pre-prosthetic therapy should be guided, according to
Körber (4), by the following 12 questions:
1. What is the extent and topography of the edentulous gaps?
2. Is the occlusal relief intact or not?
3. What is the periodontal status of the abutment teeth?
4. Is it necessary to immobilize the remaining teeth?
5. Are occlusal relationships normal or pathological?
6. Are occlusal ratios physiological or not?
7. Is mandibular dynamics disturbed or not?
8. Are occlusal stops multiple, symmetrical, and uniform?
9. Is neuro-muscular function normal or disturbed?
10. What is the quality of oral hygiene?
11. Is preventive action needed for dental caries of the remaining teeth?
12. Does individual aesthetics need improvement or not?
Prosthetic treatment is dictated by:
- The number of remaining teeth.
- Their topographical arrangement.
- The existing occlusal stops.
- The periodontal status of each abutment tooth.
The analysis of occlusal relief integrity is performed both in the oral cavity and, more
accurately, on study models that must faithfully represent the situation in the oral cavity.
Prosthetic restoration should precisely replicate the occlusal relief of the opposing teeth
(5). In cases where both arches are being treated, fixed prosthetic restorations for each
arch will be designed in an articulator, considering the principles of functional occlusion
and the individual characteristics of mandibular position and movements.
1. Preprosthetic Periodontal Treatment
The periodontal status of the future abutment teeth is crucial for the long-term
success of the upcoming restoration. Before commencing any prosthetic treatment, it is
essential to provide appropriate periodontal therapy for each abutment tooth. In cases
where teeth exhibit pronounced mobility, this can be reduced through guided tissue
regeneration techniques and endodontic treatment for teeth with this issue.
For teeth with periodontal conditions, it is crucial to reduce the force arm and direct
occlusal forces along the long axis of the abutment teeth by establishing functional
occlusion. Malocclusions result in the mobilization of abutment teeth. Abutment teeth
that are mispositioned (tilted, egressed, extruded) can be orthodontically corrected if the
patient is willing to accept the treatment plan.
Teeth with significant mobility should be temporarily stabilized during preprosthetic
treatments to prevent dental migration and promote tooth stability until the periodontal
therapy is completed.
Normally, patients have two types of occlusion:
- Point centric, where the MIP (Maximum Intercuspation Position) coincides with the
CR (centric relation).
- Long centric, where MIP does not coincide with CR.
Some patients may have interferences that lead to lateral, protrusive, or retrusive
jaw movements. These interferences should be identified and eliminated during
preprosthetic treatment so that the patient can adapt comfortably.
When assessing mandibular dynamics, the patient should perform mouthopening movements. In cases where there is asymmetry in the movement, it may be
due to myalgia or arthralgia or prolonged functional disorders that need to be identified
and addressed.
Patients who do not maintain proper dental hygiene should be motivated to
achieve proper hygiene. Otherwise, prosthetic restoration will have a limited lifespan.
Before commencing prosthetic treatment, the entire oral cavity should be
cleaned, and all carious lesions must be removed.
In the stage of selecting abutment teeth, the following factors should be
considered (1):
a) Status of the dental crowns:
- Intact
- With lesions
- With restorations
- Absent
b) Root morphology
c) Crown-to-root ratio
d) Endodontic status:
- Vital teeth
- Non-vital teeth
- Teeth with complete or incomplete root canal fillings
- Teeth with apical resection
e) Tooth implantation:
- Normal
- Tilted
- Twisted
When selecting an abutment tooth, its crown may not always have an ideal
morphology and may present carious lesions, dystrophies, traumatic injuries, which
need to be corrected through reconstruction. Thanks to new materials and modern
techniques, most of these crown lesions can be restored.
Crowns with extensive and deep lesions can also be salvaged. These may
require:
- Endodontic treatment, followed by the reconstruction of the coronal portion using
corono-radicular devices that can be custom-made in the dental laboratory or prefabricated metal or non-metal devices like posts.
- In cases of short clinical crowns due to dental abrasion or when crown lesions extend
subgingival, surgical lengthening is necessary to increase the retention surface for the
future crown.
- Guided by the principle that the edge of the future prosthetic restoration should be
supported by healthy dental tissues, in cases where crown lesions extend subgingival,
the same approach is adopted, and crown lengthening is extended beyond the restored
area to achieve the effect of encirclement or ferrule effect.
There are two ways to achieve crown lengthening: either through gingivectomy or
through gingivo-alveoloplasty.
Gingivectomy is typically performed in cases of gingival hyperplasia and can be
done using:
- A scalpel
- Electrocautery
- Laser
- Zirconia oxide burs for mucosal procedures.
Gingivo-alveoloplasty is performed when a greater crown lengthening is
required, and intervention on the alveolar bone is necessary for remodelling.
Both crown lengthening procedures are also used in situations where, for
aesthetic reasons, it is necessary to modify uneven gingival margins to achieve a
special aesthetic effect in patients with a gummy smile. To ensure predictable results,
surgical guides and provisional restorations should be used to guide the healing
process.
The root configuration of the abutment tooth influences its value because all
occlusal forces acting on it are transmitted to the alveolar bone through the root. Oval
or flattened roots with a greater buccal-oral diameter than mesio-distal ones are more
valuable than round roots in cross-section. Molars with divergent roots provide better
periodontal support than molars with converging roots and a conical shape.
Fig. 3.3. The molar with divergent roots (a) is a more valuable abutment than one with
fused roots (b).
The buccal-oral diameter of the root of the maxillary premolar (a) is larger than
that of the maxillary central incisor, which has a spherical root in cross-section (b). This
makes the premolar a more valuable abutment tooth, even though both have the same
root surface area.
In the case of single-rooted teeth, those with long roots and potential curves in
the apical third are preferred. In the situation of multi-rooted teeth with periodontal
issues, there are significant challenges in achieving prosthetic restoration. The biggest
problems arise when the periodontal lesion leads to exposure of the furcation because it
is very difficult for the clinician to access the area for scaling and root planning, and on
the other hand, the patient cannot properly clean this area. If these two problems can be
satisfactorily resolved, these teeth have a better prognosis than a single-rooted tooth
with the same degree of implantation.
The root morphology of the abutment tooth is crucial in the periodontal therapy
preceding prosthetic treatment. SRP (scaling and root planning) is the treatment of
choice for achieving therapeutic success. Ideally, attempts should be made to achieve
guided tissue regeneration through bone augmentations and connective tissue grafts to
cover these defects and increase the degree of implantation of these teeth.
The crown-to-root ratio is represented by the length of the crown measured
from the incisal or occlusal edge of the tooth to the level of the alveolar crest, relative to
the length of the intraosseous root. Ideally, the crown-to-root ratio is 1/1.5-2. The
minimum acceptable ratio for abutment teeth is 1/1.
In the presence of an equal periodontal ligament space, the displacement of the
crown of a tooth with reduced bone support is greater than that of a tooth that has not
experienced bone loss (Nyman and Lindhe).
Root exposure is considered a pathological retraction of the supporting
periodontal tissue that occurs because of minor or major periodontal conditions. This
periodontal retraction alters the clinical crown-to-root ratio.
During repeated marginal gingivitis and periodontitis, gingival retraction and
alveolar bone loss occur, leading to a decrease in the degree of implantation of the
tooth in the alveolar bone. As a result, the extracoronal force arm of the tooth increases,
amplifying the harmful forces acting on the tooth.
A crown-to-root ratio less than 1/1 is only accepted in cases where the
antagonists of fixed restoration are represented by artificial teeth (complete dentures).
In the case of teeth with periapical pathology that can be resolved through
conservative endodontic treatment, the crown-to-root ratio will not be affected. However,
when periapical pathology can only be resolved surgically, efforts should be made to
minimize the amount of root resection so that the crown-to-root ratio is minimally
influenced.
The endodontic status of these abutment teeth is a crucial element in their
selection. The preference is for using vital abutment teeth. However, in many situations
due to past carious conditions, direct pulp capping, migrations, torsions, or lack of
parallelism, pulpectomy may be necessary for prosthetic purposes to prevent
complications resulting from pulp necrosis. This is because addressing endodontic
problems later requires perforating the prosthetic restoration to gain access to the root
canals. The loss of hard dental tissues by creating an access cavity for subsequent
endodontic treatment results in undermining the resistance of the abutment tooth, and
crown perforation reduces its retention.
Future prosthetic abutments may have an correct endodontic treatment, but in
most cases, root canal treatments are incorrect, often being incompletely obturated. In
fortunate cases, incomplete treatments do not result in periapical pathology, but most of
the time, incomplete obturations lead to periapical pathology. Depending on the quality
and the length of the root canal obturation, the approach to this problem is either the
correct redoing of the root canal treatment or the surgical resolution of periapical
pathology by root apex resection. The second option has a significant drawback,
namely a decrease in root implantation.
The decision not to perform pulpectomy for prosthetic purposes can lead to false
conclusions and incorrect clinical decisions that will be regretted later, causing
discomfort to both the patient and the dentist, and ultimately increasing costs.
Evaluating the periodontal status of future abutment teeth is essential for the
long-term success of the future prosthetic restoration. The degree of periodontal
involvement in abutment teeth can range from mild, as seen in gingivitis, where only the
gingiva is affected due to irritation from dental plaque. This type of gingivitis can be
relatively easily resolved by changing the patient's oral hygiene habits, adopting proper
toothbrushing techniques, and using additional oral hygiene tools such as dental floss,
interdental brushes, and oral irrigators.
In the case of periodontitis, the problems become more complicated because
other components of the periodontium are involved, including the periodontal ligament,
alveolar bone, and root cementum.
Gingivitis and periodontitis should be treated during the pre-prosthetic treatment
phase because dental mobility and pain worsen during chewing, causing discomfort to
the patient.
Inflammation of the periodontium reduces the ability of abutment teeth to respond
to functional demands. Therefore, prosthetic restorations designed to stimulate healthy
periodontal tissues can have an irritating effect on periodontal tissues affected by
periodontal disease.
Periodontal diseases often lead to changes in tooth positions. If prosthetic
restorations are applied to teeth without prior periodontal therapy, they will further irritate
the periodontium and reduce the lifespan of the abutment tooth.
Fixed prostheses made on models based on impressions of gingiva affected by
periodontal disease will not fit correctly when the gingiva heals after subsequent
periodontal treatment. Any periodontal healing is accompanied by gingival recession,
which exposes the edge of the prosthetic restoration and creates inappropriate retentive
spaces between teeth, leading to plaque accumulation and resulting in inflammation of
the residual alveolar crest mucosa and gingiva of the abutment teeth, perpetuating this
vicious cycle.
To establish the future margins of the preparation on the future abutment tooth,
the position of the healthy gingival sulcus must be determined before starting the
preparation.
For patients with advanced periodontal disease, the treatment sequence should
be as follows:
- Irrecoverable teeth should be extracted, and temporary prostheses with provisional
cervical margins should be made, which will be contoured after periodontal healing.
- Completion of periodontal treatment. Teeth with divergent roots are more valuable
abutments than those with fused roots.
- Approximately two months after completing periodontal treatment, when the gingival
tissue and gingival sulcus have stabilized, the cervical contour of the preparation is
contoured.
Periodontal therapy begins with a clinical examination, where the patient's oral
hygiene level is assessed. A periodontal evaluation at the gingival level assesses the
color, texture, tendency to bleed, and contour of the gingiva. Then, the height of
keratinized gingiva and attached gingiva is evaluated.
The examination of the gingival sulcus is done by periodontal
probing after complete cleaning and the removal of all gingival irritation
factors. The examination of periodontal pockets is mandatory by
periodontal probing and radiological examination.
These examinations can determine whether the periodontal
pockets are false or true. False periodontal pockets appear because
of the increase in volume of the gum in response to an irritating factor
without affecting the periodontal ligament. This type of lesion falls
under the category of gingivitis.
True periodontal pockets occur with the destruction of
supporting periodontal tissue. These can be classified into supraalveolar pockets, where the bottom of the periodontal pocket is located
coronally to the level of the adjacent alveolar bone and infra-alveolar
pockets, where the bottom of the pocket is positioned apically to the
level of the adjacent bone.
The presence of true periodontal pockets requires preprosthetic periodontal treatment until the moment when we obtain
healthy periodontal tissue.
Assessment of abutment tooth mobility is a vital stage in the
lifetime of the future prosthetic restoration(2). Physiologic mobility in
single-rooted teeth is up to 0.15 mm and in multiple-root teeth it is 0.10
mm. Increased tooth mobility (greater than physiological) can be
transient, reversible or irreversible.
Transitory tooth mobility usually occurs after laborious tooth
extractions, in teeth that have undergone periodontal surgical
procedures, or in patients who have received orthodontic treatment.
Usually, this type of tooth mobility is reversible after the natural
reorganization of the periodontium and tissue healing.
There are three degrees of tooth mobility:
Grade I tooth mobility is slightly more pronounced than
physiological mobility, but the incisal edge or occlusal surface during
tooth movement does not exceed 1mm in the buccolingual direction.
Grade II tooth mobility involves movement both in the vestibulooral and mesio-distal directions, exceeding a value of 1 mm;
Grade III tooth mobility is highly pronounced and occurs in the
vestibulo-oral, mesio-distal and axial directions.
Increased physiological tooth mobility can occur during
pregnancy, tooth eruption, in acute inflammations of the apical
periodontium or in teeth with hooks that have functionally overstressed
the tooth. This type of mobility is reduced when the causative factor is
removed.
Pathological tooth mobility appears in:
- periodontal disease with the reduction of the periodontal
ligament and the reduction of the alveolar bone level;
- gingival inflammation extends to the supporting ligament and
bone;
- physicochemical changes due to hormonal treatments.
- due to osteomyelitis, tumors, traumas, traumatic occlusion
and bruxism;
- due to metabolic diseases such as diabetes.
Transient tooth mobility can be of a prosthetic nature, for
example a hook or a means of stabilizing a removable prosthesis or
an incorrectly distributed extension can lead to the appearance of tooth
mobility, but when the determining factor is removed the mobility will
be reduced.
Superficial
or
deep
periodontal
inflammations,
tartar
accumulations, septic pulpal inflammations that spread into the
periodontal space can increase tooth mobility.
Dental migrations of the tilting type led to a modification of the
axis in which the tooth receives forces, lead to the appearance of
premature contacts and interferences leading to overloading of the
tooth and the widening of the periodontal space. In all these situations,
if the causative factor is detected and removed, dental mobility will
disappear.
If the periodontal insufficiency and the destruction of the
alveolar bone is massive, the inversion of the crown-root ratio occurs
in favour of the root and the force arm increases, which leads to the
development of irreversible dental mobility. In this situation, the only
treatment that can help is guided tissue regeneration.
Many times, the abutment teeth are in malposition. The
malposition can be primary or secondary to extractions, periodontal
diseases, interferences, traumatic occlusion. Usually, in patients who
had extractions and did not follow prosthetic treatment, a series of
dental movements of the teeth adjacent to the edentulous gap and of
the antagonistic teeth to the gap begin. These dental movements
occur due to the loss of contact areas with neighbouring teeth.
Usually, the adjacent teeth to the edentulous gap begin to
migrate towards each other through a translational movement, which
later, under the influence of occlusal forces and the interferences
caused by the displacements, turns into tilting and sometimes rotations
of the teeth occur. The tooth opposing the gap, no longer having an
antagonist, begins to egress or extrude. These tooth movements alter
the occlusal plane and reduce the available prosthetic space thus
making it difficult to develop an optimal prosthetic plan. In the situation
where the movements of the teeth are not very pronounced,
corrections can be solved by selective grinding, but the significant
disadvantage will be that the abutment teeth will no longer receive the
occlusal forces in the long axis, these forces will act para-axially, and
over time a periodontal overload of the abutment tooth will occur. If the
abutment tooth has a tipping degree greater than 25º, it can no longer
be used as a post tooth because the occlusal forces will act completely
outside the long axis of the tooth and will accelerate the destruction of
the supporting periodontal tissue and the resorption of the alveolar
bone.
Orthodontic treatment aims to correct tilted, rotated or
egressed/extruded teeth so that the occlusal plane is corrected, and
by repositioning the abutment teeth, the contact points with
neighbouring teeth are restored, the gap is recalibrated and the axis
of the remaining teeth can be corrected so that the abutment teeth or
the teeth adjacent to an implant prosthetic restoration to be able to
correctly receive the occlusal forces. Through the changes obtained
with the help of orthodontic treatment, the aesthetic aspect of the final
restoration is improved, and optimal conditions can be created for the
realization of a prosthetic restoration that will function in optimal
conditions for as long as possible.
Fig.3.4. Fixed orthodontic device for correcting the position of
the second molar tilted towards the mesial: A) occlusal aspect; B)
vestibular aspect (1)
By correcting the axes of the remaining teeth from a
prophylactic perspective, the retentive and food impact areas are
solved, thus preventing the appearance of periodontal pockets.
Interdisciplinary orthodontic-prosthetic treatment has the result
of offering the possibility of increasing the quality of prosthetic
treatment by eliminating compromise solutions, but unfortunately,
many patients and doctors refuse this type of treatment due to the time
factor, preferring faster solutions but which unfortunately are more
radical and invas
Chapter 4.
DENTAL PREPARATIONS IN FIXED PROSTHODONTICS
Because dental hard tissues do not have the regenerative
potential that most tissues of the human body have, when they are
lost due to carious or traumatic processes, they must be replaced in
order to restore form and function. Most of the time, this replacement
involves a preparation/preparation of the remaining tissues in order
to optimize the consecutive clinical-technical stages. Therefore, it is
necessary to consider biological, mechanical and aesthetic factors,
which are interrelated.
The preparation of the teeth to achieve correct and durable
prosthetic restorations must take into account all these factors at the
same time, and their simultaneous maximum satisfaction is often
impossible. Thus, the prosthetist is often put in a position to find the
best compromise.
Biological considerations:
- Protecting adjacent teeth during preparation;
- Protection of soft tissues (marginal periodontium, lips,
cheeks);
- Protecting the pulp from thermal, chemical, bacterial trauma;
- Conserving dental hard tissues (axial preparation, marginal
preparation, placement of prosthetic restoration edges, marginal
adaptation, marginal geometry);
- Occlusal considerations;
- Preventing fractures.
Mechanical considerations:
- Retention form (amplitude and direction of dislocating forces,
geometry of the preparation – height, diameter, taper, size and
texture of the prepared surface, cementation interface, cement type,
thickness of the cement film);
- Stability;
- Resistance.
Aesthetic considerations:
- all-ceramic full crown;
- Total physiognomic metal-ceramic crowns;
- New generation polymers;
- Edges placed subgingival.
These principles are further elaborated in specialized
textbooks (such as Rosenstiel, Schillingburg, Bratu) and are not the
focus of this work. However, we will emphasize essential points that
help students and young dentists in their day-to-day practice.
1. Preparation must ensure maximum preservation of
dental hard tissues.
In the case of vital teeth, conservative preparation minimizes
the possibility of adverse pulpal effects following the preparation
trauma itself, as well as during other clinical stages (gingival sulcus
displacement, impression, temporary fixed prosthesis fabrication,
framework try-in/other checks, temporary/final cementation, etc.).
In the case of non-vital teeth, conservative preparation
enhances the structural resistance of the tooth, minimizing the risk of
fracture under masticatory forces.
A minimally invasive and maximally conservative approach
can be achieved by:
- Choosing inlays and partial crowns instead of full crowns.
- Ensuring minimal taper of the preparation.
- Anatomical preparation of the occlusal surface.
- Opting for a minimally invasive marginal/terminal design.
- Keeping apical preparation minimal/minimal invasion at the
gingival sulcus.
- Orthodontic repositioning when a convenient preparation for
parallelism among multiple abutments would compromise pulp
vitality.
2. Any preparation, for any type of fixed prosthetic
restoration, involves a certain degree of tissue sacrifice, no
matter how minimally invasive the restoration may be. Exceptions are
certain no-prep restorations. This applies both to single-tooth
restorations and when preparing for an abutment of a fixed prosthetic
restoration. Thus, the student and young dentist must make a correct
and informed decision when choosing a specific prosthetic
restoration over another. Ideally, when the clinical situation allows,
the restoration of choice should be a conservative one. In case of
failure, the practitioner can then consider a more invasive restoration.
3. An optimal preparation is essential for the adaptation of
the prosthetic restoration, ultimately influencing the long-term
success of the treatment.
4. There is no clinical consensus regarding the best
preparation technique or the best marginal preparation, which
can indeed make therapeutic decisions challenging for students and
young dentists. However, there are certain recommendations aimed
at improving marginal adaptation, enhancing aesthetics, and
minimizing marginal stress levels.
5. There is no clinical consensus even in recommending
the ideal instrumentation for a specific preparation (Beuer).
6. In current prosthodontics, the concept of overcontouring is
relative (BOP technique - Ignacio Loi). Overcontouring is allowed
under the condition that the emergence profile is correct, the
marginal area of the prosthetic piece is properly shaped, finished,
and polished, and its marginal adaptation is precise.
We will not dwell on traditional preparations that, in the
absence of current adhesive systems and techniques, were designed
with additional retention features such as grooves, pits, boxes,
assuming a greater tissue sacrifice to provide retention for fixed
prostheses.
Considering that classical preparations are extensively
detailed in dedicated specialty textbooks and are mostly focused on
mixed metal-ceramic and metal-polymeric fixed prosthetic
restorations, we will emphasize innovative, modern preparations, and
concepts oriented towards maximum tissue conservation in the
following. It's important to note that preparations should be kept
within enamel, and unnecessary dentin exposure should be avoided.
Modern preparations can be successfully used for mixed
metal-ceramic fixed prostheses, provided that a correct design is
implemented, and modern adhesive protocols characteristic of allceramic systems are used.
Any fixed prosthesis requires a certain minimum thickness to
ensure the mechanical strength of the material/materials from which
it is made. Thus, a less resistant material (e.g., feldspathic ceramic)
requires a greater thickness than a material with higher resistance
(e.g., zirconium oxide).
A layered mixed fixed prosthesis requires a larger prosthetic
space than a monolithic fixed prosthesis. The required thickness of a
fixed prosthesis must always be correlated with the prosthetic space,
both axially and incisal/occlusal.
Therefore, when it is necessary to achieve an increase in
volume through prosthetic treatment, tissue reduction during
preparation will be less (or non-existent in no-prep treatments)
compared to situations where this is not desired. Examples include
cases with pronounced dental wear, abrasion, attrition, erosions,
certain traumas, where volume augmentation is done purely
additively, sometimes entirely non-invasive, through vestibular and
palatal veneers, as well as adhesive-fixed table-top restorations to
hard dental tissues. In some cases, minimal tissue invasion is
required by rounding and finishing certain edges to facilitate
subsequent clinical and technical steps.
A thorough case documentation and planning is essential
before commencing the treatment stages.
Preparation for dental crowns
In relation to the free gingival crest, the terminations can be
placed supragingival, epigingival, or subgingival. It is universally
accepted that supragingival placement offers the most advantages.
The termination should follow the free gingival crest, parallel to the
clinical crown, concave towards incisal/occlusal on the vestibular and
oral aspects, and convex towards incisal/occlusal on the proximal
surfaces (mesial+distal). This is essential in preparing teeth with
periodontal involvement.
The following preparation steps are aimed at teeth in an ideal
position, whose longitudinal axis coincides with the prosthetic axis of
the future restoration. In cases of migrated, tilted, translated, rotated,
extruded, or intruded abutment teeth, the ideal treatment of choice is
interdisciplinary, involving orthodontics followed by prosthetics.
While there is currently a consensus regarding the preparation
of axial and occlusal surfaces, as well as the incisal edge, there are
no specific guidelines for the universal use of a particular marginal
preparation/ideal termination.
Setting aside older classifications of prosthetic terminations
associated with crown preparations, in modern prosthodontics, we
can systematize as follows:
1. Preparations without a precise margin, also known as
vertical preparations (similar to tangential, knife-edge, or feather
edge preparations), brought to the forefront and strongly supported
by Ignacio Loi through the BOPT technique.
2. Preparations with a precise margin, also known as
horizontal preparations, including preparations with a shoulder and
chamfer, as well as their variations (straight shoulder, straight
shoulder with rounded internal angle, inclined shoulder, bevelled
shoulder, deep chamfer, long chamfer, etc.). In this category, we will
exemplify and describe in detail the preparation with a straight
shoulder with a rounded internal angle and the chamfer preparation.
These preparations share with traditional shoulder preparations only
the advantage of a precise margin, without the tissue invasion
typically associated with traditional shoulder preparations.
It's about rounded internal angle shoulders and conservative
chamfers, measuring 0.3-0.8mm, rather than extensive straight
shoulders at a 90º angle with widths of 1mm, 1.2mm, or even 1.5mm,
as described in traditional techniques and recommended for metalceramic and metal-polymer fixed prostheses, as well as traditional
all-ceramic/polymer jacket crowns.
Advocates of vertical preparation argue for its universal
indications based on:
1. Minimally invasive nature: Vertical preparation is
characterized by its minimally invasive approach, preserving more of
the natural tooth structure, which is beneficial for long-term dental
health.
2. Creation of a terminal zone instead of a line: This approach
allows dental technicians greater flexibility in achieving marginal
adaptation and optimal aesthetics by creating a terminal zone rather
than a sharp line.
3. Biological considerations: Vertical preparation can have
biological advantages by modifying and maturing periprosthetic
gingival epithelium. This leads to the subsequent development of
healthy epithelium through directed over contouring, often facilitated
with provisional restorations. Practically, this results in a new
emergence profile, eliminating the amelocemental junction and
creating a new cemento-prosthetic junction. This allows for superior
aesthetics through the harmonization of adjacent preparation
margins and the achievement of optimal symmetry.
The adoption of minimally invasive concepts in modern
prosthodontics has been made possible due to the evolution of
dental materials. Currently, optimal aesthetic results can be achieved
using polycrystalline ceramic materials with increased strength, even
though a decade ago, these materials did not excel in terms of
aesthetics.
Research in the field of materials for fixed prostheses has led
to:
- Improvement in the aesthetics of polycrystalline ceramic
materials through increased translucency.
- The ability to create monolithic fixed prostheses from lithium
disilicate and zirconium oxide ceramic materials.
- The possibility of creating thinner restorations by enhancing
the intrinsic mechanical strength properties of materials, allowing for
more conservative preparations.
- Enhanced quality and properties of adhesive agents and the
development of clear adhesive fixation protocols, leading to improved
durability of fixed prostheses (e.g., primer 10-MDP for adhesive
bonding of ZrO2 fixed prosthetic restorations).
In a didactic manner, we will divide the preparation stages into common stages and
specific stages (preparation of the terminal zone). In cases where an increase in
coronary volume is desired in the end, preparation will be performed through a
previously obtained mock-up.
Preparation for veneer crowns
In the anterior region:
1. Preparation of the incisal edge
In the posterior region:
1. Preparation of the occlusal surface
For the upper incisors
For didactic purposes, this can be divided into:
Typically, it is performed perpendicular to the
1.1. Reduction of the internal occlusal surface;
direction of action/axis of the mandibular frontals in
1.2. Bevelling of the supporting cusps.
maximum intercuspation.
Thus, in the case of a psalidodont occlusion, the
Reduction should be carried out while respecting the
section direction will be oriented buccal-palatal,
anatomy of the occlusal surface, conservatively, ensuring
respectively inciso-cervical.
maximum thickness of TDD (tooth tissue remaining) near
In the case of a labiodont ( head to head)occlusion,
the pulp horns. This ensures correct adaptation and
the preparation of the incisal edge will be done
optimal resistance for future fixed prosthetic restorations
straight.
and facilitates subsequent clinical and technical steps.
For the lower incisors, the incisal reduction will be
performed perpendicular to their axis.
It is considered optimal to obtain a prosthetic incisal/occlusal clearance of 1.5-2mm. Anatomic reduction can be
achieved through the prior preparation of depth-marking grooves made with specific instruments and by using
silicone condensation keys/conformers.
Methods for preparing orientation grooves
1. Classic Method: According to Schillingburg, Rosenstiel, Bratu, using cylindrical-conical diamond
instruments with rounded tips.
2. Modern Method: Using specialized instruments designed for this purpose, which enable controlled and
uniform penetration into the TDD (remaining tooth tissue) at a desired depth while following the anatomy
of the occlusal surface. (ex. DM05, DM10, DM15, DM20 – Komet, MADC – NTI, 828 – Meisinger) These
instruments also allow for the creation of a more favourable pattern or layout of the grooves, making it
possible for subsequent preparation perpendicular to their direction. This ensures increased tissue
preservation by avoiding the engagement of rotary instruments in the grooves and further deepening. In
case these special instruments are unavailable, a similar pattern of orientation grooves can be created
using spherical diamond instruments with a diameter identical to the desired reduction.
1.1.
Reduction of the internal occlusal surface is achieved by
removing the islands of remaining TDD (tooth tissue) between the
orientation grooves, using cylindrical or cylindrical-conical
diamond instruments with rounded tips, oriented buccal or palatal
and kept parallel to the cuspal inclintion being prepared,
performing mesio-distal brushing movements.
1.2.
Bevelling the supporting cusps is an extremely important
stage, common to all extra-coronal preparations on teeth in the
lateral areas of the arches. It ensures the attainment of optimal
prosthetic space at this level, depending on the material strength
of the future fixed prosthesis.
In this case as well, the creation of depth orientation grooves is
recommended, either using the classic or modern approach with
specialized instruments. Bevelling the supporting cusps is done by
maintaining cylindrical or cylindrical-conical diamond instruments with
rounded tips, in a buccal-oral direction, parallel to the external cusp
incline, at a 45-degree angle to the long axis of the tooth. Precise, fine
mesio-distal movements are performed during this process. As the
preparation progresses toward the proximal areas, rotational movements
can be associated, following the tooth's anatomy closely.
Preparation of the axial surfaces
2. Preparation of the vestibular surface
It will always be performed anatomically. Thus, both in the anterior and lateral areas of the arches, the
preparation will be carried out in two planes, delimited by the anatomical equator.
2.1.
Preparation in the incisal/occlusal plane, parallel to the vestibular surface at a supra-equatorial
level.
2.2.
Preparation in the cervical plane, along the tooth's axis, respecting the axis of insertion of the
future fixed prosthesis.
In the first stage, orientation grooves will be prepared. For objective reasons, we recommend creating horizontal
grooves, which allow for a more conservative subsequent preparation technique. Their depth should be
approximately 1.5mm in the equatorial area and 1.5 to a maximum of 2mm towards the incisal/occlusal area.
The preparation in the incisal/occlusal plane (supra-equatorial) will be performed using cylindrical or
cylindrical-conical diamond instruments with rounded tips. These instruments should be maintained
inciso/occluso-cervically parallel to the vestibular surface at this level, with brushing movements in the mesiodistal direction across the tooth surface. Experienced practitioners may also use specialized instruments such
as flame-shaped or tapered ones for this purpose.
Preparation in the cervical plane (sub-equatorial) is carried out using specific instruments,
depending on the desired margin termination/preparation:
2.2.1. Cylindrical or cylindrical-conical diamond instruments with rounded tips, for preparations with
chamfers.
2.2.2. Cylindrical or cylindrical-conical diamond instruments with flat tips and rounded angles, for
preparations with a straight shoulder and rounded internal angle.
2.2.3. Flame-shaped diamond instruments, for vertical preparations without a precise limit.
The advantages of cylindrical instruments lie in the fact that they occupy a smaller volume compared to
cylindrical-conical ones for the same tip shape. This allows for better access to proximal areas, minimizing the
risk of touching the proximal surfaces of adjacent teeth to the preparation. On the other hand, to achieve
optimal convergence of opposing axial surfaces, these instruments need to be tilted, requiring more
experienced practitioners and greater attention; otherwise, it may result in retentive areas.
2.2.1. Preparation with a chamfer of the cervical area of the vestibular surface
It can be achieved with:
-
Cylindrical-conical instruments with rounded tips maintained along the tooth's axis.
Cylindrical instruments with rounded tips inclined with the base toward the tooth's axis and the tip
outward, so that in the end, an ideal convergence of 6º is achieved with the cervical area of the
opposing axial surface (oral).
It is crucial that for a flawless chamfer-type preparation configuration, the diamond instruments with
rounded tips are inserted into the marginal TDD (tooth tissue remaining) for half of their diameter,
preventing the creation of a preparation into the canal and an unsupported enamel ledge in the
marginal area.
We recommend using cylindrical/cylindrical-conical instruments with a tip radius of 0.3-0.8mm, and in
the case of cylindrical-conical instruments, an angle of 2-3º with the axis of the bur, ideally ensuring a
convergence of 4-6º between opposing axial walls. Using these instruments, tissue reduction at the
marginal level ranges between 0.3-0.8mm.
2.2.2. Preparation with a rounded internal angle shoulder of the cervical area of the vestibular surface
The preparation technique is similar to the one described earlier. Cylindrical-conical instruments with straight
tips and rounded angles, maintained along the axis, or cylindrical instruments with straight tips and rounded
angles, inclined at 2-3º relative to the tooth's axis, will be used.
We recommend creating shoulder configurations of 0.3 to a maximum of 1mm, considering that all current
classes of materials designed for fixed prostheses meet the mechanical strength requirements, especially when
a well-established adhesive fixation protocol is used.
2.2.3. Vertical preparation of the cervical area of the vestibular surface (vertical preparation, tangential)
The preparation is carried out using flame-shaped diamond instruments, maintained along the tooth's axis and
moved in the mesio-distal direction, with the tip following the contour of the free gingival crest. The objective of
this preparation is to achieve at this level a terminal transition zone between the prepared area and the
unprepared remaining tooth tissue (TDD) that is smooth and without any visually detectable or palpable
demarcation.
Vertical preparation can be performed both supragingival and subgingival, but within the BOP (Biologically
Oriented Preparation Technique) described by Ignacio Loi, it is done subgingival. Vertical preparation offers
conservative advantages, ensuring minimal reduction of hard dental tissues around the neck of the tooth.
Fixed prostheses obtained on teeth prepared vertically will invariably have overcontour, with a different
emergence profile compared to the original tooth. However, this is a controlled, non-retentive over contouring,
designed correctly to protect the marginal periodontium, provided there is optimal marginal adaptation of the
prosthetic piece and minimal invasion of the sulcus.
3. Preparation of the oral surface
In the anterior region
In the posterior region
For the mandible - the technique described for the
We will uniformly address the preparation of the
preparation of the cervical area of the vestibular surface
oral surface of both maxillary and mandibular
will be used. Please refer to sections 2.2.1, 2.2.2, 2.2.3.
anterior teeth, emphasizing the similarities rather
Objectives:
than the differences, as clinical variety is a distinct
-
Maintain the correct axis.
consideration.
-
Achieve the ideal convergence of 6º.
For any maxillary or mandibular anterior tooth,
-
Follow the contour of the free gingival crest.
there is generally a concave area toward the
For the maxilla - the technique described for the
incisal edge and a convex area toward the
preparation of the cervical area of the vestibular surface
cervical region.
will also be employed. Please refer to sections 2.2.1, 2.2.2,
In general, for a guided, minimally invasive
2.2.3.
preparation, we recommend the use of horizontal
orientation grooves and silicone keys.
Objectives:
To prepare the concave area of the oral surface,
-
Maintain the correct axis.
instruments like rugby/football American-shaped
-
Achieve the ideal convergence of 6º.
diamond burs, egg-shaped burs, etc., will be
-
Follow the contour of the free gingival crest.
used.
The choice of diamond instruments will be based on the
For the convex area, corresponding to the cervical
desired marginal preparation, with cylindrical-conical
region (also referred to as subcingular - Bratu),
diamond instruments maintained along the tooth's axis and
the preparation technique described for the
cylindrical instruments inclined with the tip outward to
cervical/sub-equatorial area of the vestibular
achieve occlusal convergence (6º) of opposing axial areas.
surface will be employed, depending on the
desired marginal preparation/termination. This
involves maintaining cylindrical-conical diamond
instruments along the tooth's axis and cylindrical
instruments inclined with the tip outward to
achieve occlusal convergence (6º) of opposing
axial areas. The tip of the rotary instrument will
follow the free gingival crest at this level, and the
preparation can be placed supra, epi, or
subgingival. Please refer to sections 2.2.1, 2.2.2,
2.2.3.
4. Preparation of the proximal surfaces
The objectives of the preparation are as follows:
-
Protecting the proximal surfaces of adjacent teeth during preparation.
-
Minimizing tissue reduction according to the desired preparation.
-
-
Achieving minimal/optimal occlusal convergence of opposing proximal surfaces.
-
-
Maintaining the preparation axis.
Following the free gingival crest.
Ensuring the marginal preparation is parallel to the free gingival crest, regardless of whether it is
placed supragingival, epigingival, or subgingival.
The proximal surfaces will be prepared using the technique described for the cervical/sub-equatorial area of the
vestibular surface, depending on the desired marginal preparation. Protection of adjacent teeth can be
accomplished using matrices such as Safeguard, Fenderwedge, metal bands, wedges, or other suitable
methods. These are recommended, especially for students and less experienced prosthodontists.
However, considering that the cervical area of the proximal surfaces is invariably located approximately 11.5mm further inside the tooth compared to the proximal contact point, preparation at this level can be
performed by separating a thin layer of tooth tissue, which can be subsequently removed using hand
instruments. Small-diameter rotary instruments (e.g., flame-shaped, tapered) have an advantage in this regard.
Among cylindrical and cylindrical-conical instruments with identical tip diameters, cylindrical ones offer a clear
advantage due to their smaller profile for the same tip diameter/curvature radius.
CAD/CAM CROWN PREPARATION GUIDE
Ideal Posterior Crown Preparation
•
Rounded Internal Angles
•
Reduction by 1.5-2 mm at the occlusal level and 1 mm at the margin.
• Chamfer preparation at the margin with an occlusal convergence ranging from 6-10o
Ideal Anterior Crown Preparation
• Reduction of 1-1.5 mm of the vestibular and lingual surfaces
• Reduction at the incisal level by 1-2 mm
•
Chamfer preparation at the margin
•
The preparation should follow a three-dimensional reduction based on the
anatomical shape of the tooth.
CONSIDERATIONS TO AVOID IN PREPARATION:
Knife-edge" or "feather-edge" margins
•
Due to possible complications in milling and the material's limitations, knife-edge or
feather-edge margins should be avoided.
Reduction at the margin (marginal level) by 1 mm with an occlusal convergence of 6-10
0
Avoiding Retentive Features
• The presence of these can lead to insufficient material thickness in the areas trapped
between these retentive features.
Avoidance of Preparations with High Convergence
• Preparations with a high degree of convergence can also create challenges during
scanning.
• To eliminate this drawback, it should be ensured that the entire margin of the
preparation is visible from the occlusal aspect.
Avoidance of Sharp Angles
If the diameter of the bur is larger than the apex of the preparation, overcontouring may
occur during milling. This can happen in cases of lower incisor preparation or when the
angles of the preparations are not rounded.
Avoidance of Thin Walls After Endodontic Treatments
One should avoid thin walls after endodontic treatments, as they may potentially lead to
fractures over time. Additionally, it should be ensured that the access area is not less
than 1.5 mm to prevent failure. Supragingival margins are ideal, as there is no need to
hide the metal collar.
PREPARATION GUIDE FOR INLAYS AND ONLAYS
• The preparation termination should have well-defined margins for easier identification.
•
• Occlusal reduction >1.5 mm
•
• Internal axial walls with 6-10 degrees of convergence 0
•
• The lines forming the internal angles should be rounded
•
• Interproximal bevel of 100-120o
•
• At the margin, the preparation edges will be capped.
•
• Isthmus depth of 1.5-2.0 mm
•
• Isthmus width of 1.5-2.0 mm
• The termination of the preparation should have well-defined angles for easier
identification.
•
• Occlusal reduction of 1.5-2.0 mm
•
Internal axial walls 6-10 0
•
• The lines forming the internal angles should be rounded
• Interproximal bevel 100-120o
ASPECTS TO AVOID IN PREPARATIONS
• To avoid over contouring, the oclusal margin design that follows the existing occlusal
anatomy cannot have a diameter smaller than 1 mm.
• Knife-edge or feather-edge margins will result in thin margins of the milled ceramic,
potentially causing fractures later on.
• Parallel walls and sharp internal angles can lead to misfit of the restoration.
• Interproximal concavities will result in over contouring and uncovered margins.
• Insufficient isthmus width will result in a fragile restoration.
GUIDE FOR VENEER PREPARATION
MARGINAL INCISAL PREPARATION
• To uniformly prepare the thickness of the enamel on the labial surface, a diamond bur
with a rounded tip and medium grit should be used.
• • The depth of the preparation will be located between 0.5-0.8 mm.
• • Incisal reduction of 1-1.5 mm.
• • The total height from margin to incisal edge cannot exceed 9.5 mm.
EXTENDED INCISAL MARGINAL PREPARATION
• Additional reductions may be necessary for masking certain deficits or for layering
techniques.
FENESTRATED PREPARATION
• Proper chamfer preparation of interproximal and cervical margins provides the
necessary space for ceramics
ASPECTS TO AVOID IN PREPARATIONS
ROUNDED INCISAL EDGE
• This type of preparation can cause tilting or fracturing of the restoration margin.
• Rounded margins
• Retentivities
• Insertion axis
• A retention-based preparation can lead to issues for digital design software due to an
inappropriate insertion axis.
CAD/CAM CROWN PREPAARATION GUIDE
IDEAL POSTERIOR CROWN PREPARATION
• Rounded internal angles
• Reduction by 1.5-2 mm at the occlusal level and 1 mm at the margin level
• Chamfer preparation at the margin level with a convergence angle
between 6-10 degrees
IDEAL ANTERIOR CROWN PREPARATION
• Reduction of 1-1.5 mm on the vestibular and lingual surfaces
• Reduction of 1-2 mm at the incisal level
• Chamfer preparation at the margin level
• The preparation should follow a three-plane reduction based on the
tooth's anatomical shape.
ASPECTS TO AVOID IN PREPARATION: "KNIFE-EDGE" OR "FEATHER" EDGES
• Due to possible complications during milling and material limitations, "knife-edge" or
"feather" edges should be avoided.
• Reduction at the margin level by 1 mm and an occlusal convergence of 6-10 degrees.
AVOIDING RETENTIONS
• Their presence can lead to insufficient material thickness in areas blocked by these
retentions.
AVOIDING HIGH CONVERGENCE PREPARATIONS
• Preparations with a high degree of convergence can also lead to scanning difficulties.
• To eliminate this issue, it should be ensured that the entire margin of the preparation is
visible from the occlusal view.
AVOIDING SHARP ANGLES
If the diameter of the bur is larger than the apex of the preparation, overcontouring may
occur during milling. This can happen in cases of preparing lower incisors or when the
angles of the preparations are not rounded.
AVOIDING THIN WALLS AFTER ENDODONTIC TREATMENTS
Thin walls after endodontic treatments should be avoided, as they can potentially lead
to fractures over time. Additionally, it should be ensured that the access area is not less
than 1.5 mm to prevent failure. Supragingival margins are ideal as there's no need to
hide the metal collar.
PREPARATION GUIDE FOR INLAYS AND ONLAYS
• The preparation termination should have well-defined margins for easier identification.
• Occlusal reduction >1.5 mm
• Internal axial walls with 6-10 degrees of convergence
• Lines forming internal angles should be rounded
• Interproximal bevelling of 100-120 degrees
• At the margin level, the preparation edges will be capped.
• Depth of isthmus: 1.5-2.0 mm
• Width of isthmus: 1.5-2.0 mm
• The termination of the preparation should have well-defined angles for easier
identification.
• Occlusal reduction: 1.5-2.0 mm
• Internal axial walls: 6-10 degrees of convergence
• Lines forming internal angles should be rounded
• Interproximal bevelling: 100-120 degrees
ASPECTS TO AVOID IN PREPARATIONS
• To avoid over contouring, the design of the occlusal margin following the existing
occlusal anatomy cannot have a diameter smaller than 1 mm.
• "Knife-edge" or "feather" edges will result in thin edges of the milled ceramic,
potentially causing fractures later on.
• Parallel walls and sharp internal angles can lead to restoration misfit.
• Interproximal concavities will cause over contouring and uncovered margins.
• Insufficient width of the isthmus will result in a fragile restoration.
PREPARATION GUIDE FOR VENEERS IDEAL VENEER PREPARATION
FLAT INCISAL MARGINAL PREPARATION
• To uniformly prepare the thickness of the enamel on the labial surface, a diamond bur
with a rounded tip of medium grit will be used.
• Preparation depth will be between 0.5-0.8 mm
• Incisal reduction of 1-1.5 mm
• The total height from margin to incisal edge should not exceed 9.5 mm.
EXTENDED INCISAL MARGINAL PREPARATION
• Additional reductions may be necessary for masking certain deficiencies or for layering
techniques.
FENESTRATED PREPARATION
• Proper chamfer preparation of interproximal and cervical margins provides the
necessary space for ceramic.
ASPECTS TO AVOID IN INCISAL MARGIN PREPARATIONS
• This type of preparation can cause tilting or fracturing of the restoration margin.
• Rounded margins
• Retentions
• Insertion axis
• Preparations with retentions can lead to issues for digital design software due to an
inadequate insertion axis.
CHAPTER 5. IMPRESSION IN FIXED PROSTHODONTICS
The faithful reproduction of all elements within the prosthetic field, i.e., transferring data
from the oral cavity to the dental laboratory, has always been a challenge for clinicians.
Impression-taking is a crucial clinical step in the fabrication of fixed prosthetic
restorations (FPR). The efficiency of prosthetic treatment through any type of FPR
largely depends on the precision of dental impressions. Over the years, both impression
techniques and materials have evolved, rendering several previously successful
methods obsolete.
GENERAL INFORMATION:
An impression represents a negative replica of the anatomical structures within the oral
cavity. Based on the impression, a working model is fabricated in the dental laboratory,
where the future fixed prosthetic restoration will be crafted. The choice of impression
materials and techniques in conventional practice is based on several criteria:
•
The fidelity of the impression material or the availability of modern equipment for
material homogenization and dosing.
•
The time available to the practitioner for impression-taking.
•
The dimensional stability of the impression material.
•
The specific characteristics of the prosthetic field closely related to the desired
fixed prosthesis.
•
The ability to store and repeatedly fabricate the model.
•
The specifics of the methods and materials available for creating the model.
Other clinical aspects to consider when deciding on the selection of impression material
and technique include:
•
The presence of cavities and undercuts that may pose challenges to accurately
recording details with the impression material.
•
Recording cervical margins becomes problematic when they are located
juxtagingival or even subgingival. If the finish line is not well-defined in the
working model, even a slight deviation, such as a few tenths of a millimetre, can
result in a conjunctival fixed prosthesis. Furthermore, a portion of the unprepared
dental surface must also be replicated. Its presence in the working model allows
the dental technician to create prosthetic surfaces that best match the
emergence profile most tolerated by the marginal periodontium. To achieve this,
temporary gingival enlargement is performed to ensure access for the impression
material.
•
The need to control oral fluids, such as blood, sulcular fluid, and saliva.
Minor bleeding may occur due to marginal periodontal inflammation (preliminary
periodontal treatment is essential) or operative aggressions during abutment
preparation using rotary instruments and gingival sulcus widening manoeuvres. Mild
bleeding is rapidly controlled if the gingiva is healthy.
Haemostatic agents like 15-20% ferric sulfate (e.g., Astringedent by Bisco) or
aluminium sulfate are used for this purpose.
Sulcular fluid secretion increases in the presence of even minor inflammation, often
becoming unavoidable during temporary gingival sulcus widening, regardless of the
technique used. When recording an area that requires precision in a wet environment, it
emphasizes the need to use impression materials capable of wetting the surfaces
effectively.
Stages of Prosthetic Field Impression
•
Fluid Control
•
Gingival Displacement
•
Impression Materials
•
Impression Trays
•
Impression Techniques
1. Fluid Control:
Fluid control represents achieving the best possible isolation of the prosthetic
field to be impressed. This is accomplished using cotton rolls, standard saliva
ejectors, and surgical aspirators. Both cotton rolls and aspirators are disposable
and need to be replaced due to moisture. Saliva ejectors, when placed
sublingually, help in suctioning saliva secreted by the salivary glands to maintain
a well-isolated prosthetic field. In cases of excessive salivary flow, whether it's
physiological or pathological, additional measures are taken to ensure a faithful
impression. This includes the use of anti-sialagogue medication such as
Atropine, Dicyclomine, or Clonidine.
Modern tools for aspiration, removal of soft tissues, and illumination, like
Isolite or Re-Leaf (Kulzer), are very helpful in preparing the operating field for
impressions.
2. Gingival Displacement (Temporary Gingival Enlargement):
Gingival displacement involves introducing elastic impression materials into
the oral cavity in a semi-fluid state. Since these materials are slightly
compressible, they may not effectively displace the free gingiva and interdental
papilla. The inherent elasticity of soft tissues contributes to creating a virtual
space in the gingival sulcus. If, however, the impression material manages to
penetrate the sulcus, the margins will inevitably become thin, fragile, and prone
to deformation under the pressure of gypsum or the materials used to create the
working model.
To achieve a faithful reproduction of the terminal area of the abutment,
gingival sulcus preparation is required, with the following objectives: temporary
displacement of gingival tissues from the tooth surfaces to expose the cervical
area and a portion of the underlying surface. This ensures vertical access for the
fluid elastomer. Creating a space horizontally to ensure sufficient margin
thickness in the impression and to avoid distortion, a prerequisite for accuracy.
Gingival retraction must be maintained throughout the intraoral hardening of the
impression material to avoid negatively affecting its mechanical properties.
Various techniques and materials for effective widening of the gingival sulcus
around tooth preparations or abutments are used, which can be divided into:
a) Mechanical methods involving unimpregnated retraction cords of various
dimensions, provisional crowns that, when removed, reveal the gingival
sulcus, and copper bands prepared to suitable abutment diameters.
Mechanical-chemical methods involving retraction cords impregnated with
substances like epinephrine, aluminium chloride, ferric sulphate, all used in
normal concentrations that do not adversely affect the periodontal status
through gingival retraction with tissue loss. In the case of epinephrine, caution
should be exercised in individuals with heart conditions due to an increase in
blood pressure and heart rate.
b) Mechanical-chemical methods
-
EXPASYL is a mixture of Aluminium chloride and kaolin that, once
injected, increases in volume. After rinsing, the gingival sulcus remains
dilated for a few minutes, allowing for a precise impression. The same
effect is achieved with products like Magic Foam cord, Retraction Paste
(3M ESPE), or Traxodent (Premier).
-Reversible hydrocolloids (agar-agar) injected at the gingival sulcus level.
Gingival retraction with retraction cords
Gingival retraction cords can be twisted, braided, which in turn can
be with a solid or hollow center. There are also woven retraction cords
that have a hollow center, being much more compressive and more
difficult to remove from the sulcus. These can absorb up to 2.5 times
more solution than the twisted ones, but they are more often cut and
caught by burs than the others.
The practical procedure for inserting retraction cords involves
checking the status of the soft tissue. It is checked for bleeding; if
bleeding is present, haemostasis is performed. If bleeding persists even
after the removal of provisional restorations, the marginal adaptation of
provisional restorations is checked, and they are finished and polished
before proceeding with the impression. The impression field is isolated
using cotton rolls, and saliva aspiration is performed simultaneously. The
depth of the gingivo-dental sulcus is measured with a periodontal probe
to choose the correct thickness of the retraction cord. The cord is
impregnated with an astringent substance, wrapped around the tooth,
and inserted into the gingivo-dental sulcus. The insertion starts from the
mesial or distal proximal area and continues incrementally until it
encircles the entire cervical circumference of the abutment, and then the
insertion point is revisited. During cord insertion, excessive pressure
should be avoided as it can cause injuries at the epithelial attachment
and gingival tissue, leading to bleeding, especially in non-keratinized and
slightly inflamed gingiva.
Various techniques or procedures for cord insertion are described in
the literature, involving the use of a single cord or two cords.
A) The single-cord technique is the choice in most cases due to
its simplicity and speed. The depth of the sulcus, measured with a
periodontal probe, dictates the diameter of the cord to be used. For
example, 1mm corresponds to #0, and 0.5mm corresponds to #00. This
single-cord technique is especially suitable for anterior and posterior
teeth, for epigingival or supragingival preparations. In the case of
subgingival preparations, the gingiva may collapse over the inserted cord,
and the impression material may not penetrate deep enough into the
gingival sulcus to create an adequately voluminous impression, resulting
in clear indications of the preparations. Therefore, after inserting the cord,
it should be visible in the sulcus, and if it's not visible, it means the cord
has been chosen too thin. Once inserted, it is left in the gingival sulcus for
about 5 minutes before careful removal, just before injecting the
impression material.
B) The double-cord technique, using two cords for gingival retraction, is a
technique that requires more time to perform and is particularly suitable for subgingival
preparations. The steps for this technique involve starting with the insertion of a thinner
cord, size #00 or #000, deep into the gingival sulcus, right at the base of the sulcus
under the margin of the preparation. This is done to have better control over moisture
and potential local bleeding. Then, a thicker cord is placed above the first cord and left
in place for about 5 minutes. This last cord is removed just before inserting the
impression material, ensuring temporary widening of the gingival sulcus.
Electrosurgical Method:
This method is performed using an electric scalpel under local anesthesia.
Contact with metallic objects inside the oral cavity should be avoided as much as
possible, and it is contraindicated for individuals with pacemakers or when the gingiva is
thin and adherent.
The effect achieved by gingival retraction should persist throughout the
impression process and should not disappear immediately after removing the cord or
widening the gingival sulcus. In this case, the effort put into achieving retraction would
become pointless.
The factors that influence the choice of a gingival retraction method include:
•
General factors: diabetes, heart disease, pacemaker, hypertension,
hyperthyroidism, allergic conditions.
•
Local factors: the placement of the cervical margin of the preparation.
•
Periodontal conditions: thin and adherent gingiva, thickness of the vestibular
alveolar bone, nature and extent of gingival recession inherent in any method.
Gingival retraction using a laser beam is easier and often does not require
anesthesia. It is performed with a diode laser and provides superior healing compared
to the electrosurgical method.
In conclusion, whichever method of gingival retraction we choose, it should be
easy to apply, not painful during insertion, have a rapid action with a sufficiently longlasting effect to allow the necessary clinical maneuvers for impression taking, should not
cause bleeding, and should not have general side effects such as increased heart rate,
elevated blood pressure, allergies, gingival recessions, or necrosis.
Impression in Fixed Prosthodontics
Impression Materials
To achieve superior impressions from a technical and clinical perspective,
impression materials must meet certain characteristics:
-
Plasticity: This represents the material's ability to be deformed and shaped
under minimal pressure and functional movements, thereby recording all
morphological and functional details of the prosthetic field without distortion.
-
Setting Time: It should be short but sufficient to meet the clinical requirements of
the impression phase.
-
Fidelity: Fidelity is the material's capacity to record the finest details of the
prosthetic field.
-
Elasticity: Elasticity refers to the material's property to allow the impression to be
removed from the prosthetic field (with varying degrees of retention) and then
return to its initial shape.
-
Mechanical Strength: This is the material's ability to resist breakage during
removal from the field, transport, and model casting.
-
Dimensional Stability: Dimensional stability represents the material's ability not
to undergo plastic deformation during removal, storage, transport, and casting
under the temperature and humidity conditions of the clinic and laboratory.
Ideally, materials with the lowest possible shrinkage coefficient are sought.
-
Compatibility with Model Materials: Both the properties of the impression
materials and those used for model casting need to be known to determine the
appropriate combinations to use.
Clinical Properties of Impression Materials
-
Hydrophilicity: The impression material should be capable of replacing moisture
and forming intimate contact with the tooth and soft tissues. It should not contain
any bubbles or voids.
-
Flexibility: The impression should be easy to remove after being fixed in the oral
cavity.
-
Elastic Recovery: An impression should return to its original size after removal
from irregular surfaces in the oral cavity.
-
Resistance to Tear: It should resist tearing after removal from the oral cavity and
when separated from the model.
-
Detail Reproduction: The impression material should reproduce even the finest
details of oral tissues and accurately transfer those details onto gypsum models.
The image below represents the main impression materials.
Reversible Elastic Impression Materials
In dentistry, reversible elastic impression materials are represented by reversible
hydrocolloids. Reversible hydrocolloids were the first elastic impression materials to
appear. The main substance is a gel based on agar-agar, which becomes plastic when
exposed to heat. The term "hydrocolloid" comes from the fact that these materials form
colloidal solutions in the form of a gel with water during the final setting phase. The term
"reversible" indicates the ability to return to a sol (fluid) state after having been turned
into a gel. Some commercial names for these materials include Hydrocolloid (KENT
DENTAL) and Hydrocolloid (KERR).
The primary component of a reversible hydrocolloid is agar-agar (gelatin). Agaragar liquefies, transitioning from a gel to a sol state between 71°C and 100°C and gels
again, transitioning from a sol to a gel state between 30°C and 50°C. The gel structure
is formed from microscopic fibers and chains of colloidal particles, creating a network
that retains water in its interstices. In dry conditions, the gel loses water through
"sweating" and retracts, while in a moist environment, the gel can absorb water through
imbibition.
The table below presents the main advantages and disadvantages of common
impression materials.
Advantages
Disadvantages
Indications
Irreversible
Rapidity, Cost-effective, Low precision
Study and diagnostic
Hydrocolloids
Immediate pouring
models, Preliminary
impression, Impression
of antagonists
Condensation Easy to use, Short
Hydrophobic,
Silicon
Weak stability
setting time, Different
Fixed prosthodontics
viscosities
Addition
Stability, Easy to use,
Hydrophobic
Silicon
Variable working/setting (problematic
time, Odorless,
subgingival
Tasteless, High
crown
precision, Multiple
impressions),
model pouring,
Some materials
Different viscosities,
release H2
Fixed
prosthodontics/implants
High tear strength,
Single or dual-phase
impression
Polyether
Dimensional stability,
Short working
Fixed
Most used in fixed
time, Material
prosthodontics/implants
prosthodontics,
becomes very
Excellent precision,
rigid after
Easy to use (automix),
setting, Cannot
Short setting time, High
pour multiple
tear strength,
models
Hydrophilic, Different
viscosities, Single or
dual-phase impression
The indications for reversible impression materials include fidelity, which is higher
than that of alginates but inferior to synthetic elastomers. They were neglected for a
while and used mostly in dental technology laboratories for duplicating models.
Corrections to the impression are not possible, but the material can be re-liquefied, and
the impression can be retaken on the same patient.
Currently, these materials are being reintroduced and successfully used in dental
offices for impression-taking of preparations (inlays/onlays, crowns, etc.) or for
duplicating models in dental technology laboratories. Contraindications for reversible
impression materials are when it is not possible to achieve quality conditioning of the
gingival sulcus, in the case of knife-edge preparations that result in very thin impression
margins, in simultaneous bilateral preparations at the premolar and molar levels, and in
patients with macroglossia and/or excessive lingual mobility.
The disadvantages of using reversible impression materials include a more
challenging and time-consuming technique, relatively brittle material, very limited
dimensional stability after gelation (the model must be poured immediately), models can
only be made from gypsum, high initial investment for accessories, and lower patient
comfort.
Irreversible Elastic Materials
Irreversible hydrocolloids:
-
Alginates
-
Synthetic elastomers:
•
Polysulfides
•
Silicones
•
Polyethers
Alginate
From a chemical standpoint, these consist of a long chain of cyclic molecules,
similar in composition to sugar. They are presented in powder form, which, upon adding
water and stirring, transforms into a paste or gel that becomes irreversible.
The commercial presentation of alginates is as a powder in a tightly sealable
container when not in use. It also includes a container for the proper dosage of the powder
into the mixing bowl to achieve the desired quality for impressions. After adding water to
the powder and mixing, it reaches a sol state, which is then loaded onto the impression
spoon, smoothed gently with moistened fingers to reduce air inclusions, and then applied
to the prosthetic field. After a few minutes (2-4 minutes, depending on the manufacturer),
the material hardens, changing from a sol to a gel-like consistency, at which point it can
be removed from the prosthetic field. The material is soft, rubbery, moist, and fragile, and
its resistance is low during removal. Due to its composition and structure, it is susceptible
to dehydration, and structural changes may occur within it. Therefore, it is recommended
to pour the gypsum model as quickly as possible (within 30 minutes) or keep the alginate
impression in a moist environment for a short period, such as covering it with a moist
towel and sealing it tightly.
Some commercial names for alginates include Alginoplast (Bayer), Xantalgin (Bayer),
Ypeen (Spofa), Orthoprint (Zhermack). They are typically presented as powder in boxes
or bags of different colors, with variations based on the type of gelation:
•
Type I (rapid gelation)
•
Type II (normal gelation)
•
And by purpose:
•
Class A (for single-tooth prostheses)
•
Class B (for arches)
•
Class C (for study models and individual impressions).
As for its composition, alginic acid is derived from marine plants. The sodium and
potassium salts of this acid have properties that make them suitable as impression
materials, and the transition from sol to gel occurs upon contact with water.
Synthetic Elastomers
Based on their composition, elastomers are divided into polysulfides, silicones
(condensation and addition types), and polyethers. Depending on their consistency, they
are classified into four categories:
•
Type I: Putties (Putty)
•
Type II: High viscosity for coarse impressions (Heavy-bodied)
•
Type III: Medium viscosity for a wide range of impressions (Regular)
•
Type IV: Low viscosity (fluid) for syringe injection techniques
Polysulfides
These materials, called polysulfides, mercaptans, thiocauchuks, or thiokols, derive
their name from the first product introduced to the market, "Thiokol," in 1953. Commercial
names include Permlastic and Unilastic (Kerr), and they are presented as two-paste
systems (base and accelerator) in three consistency variants.
Composition: The base primarily contains a polysulfide polymer, while the accelerator
contains lead dioxide. Due to the lead dioxide, these materials are dark brown or gray
and have an unpleasant odour due to sulphur.
Properties:
•
Hydrophobic
•
High, medium, or low consistency
•
Excellent dimensional stability with a contraction of 0.40-0.45% over 24 hours
•
Very good fidelity for fluid forms, decreasing with increased viscosity
•
Good mechanical strength
•
Shelf life of 18 months
•
Radiopacity
Disadvantages: Unpleasant odour and long setting time.
Indications:
•
Chitinous variants are used in double-mix techniques as support materials for fluid
ones.
•
Variants with normal consistency are used in total and partial edentulism for the
final impression.
•
Fluid variants are used to capture fine details during the fabrication of single-tooth
prostheses and bridges.
Regarding contraindications, these materials have virtually no contraindications regarding
the type of impressed field but target individuals who exhibit intolerance (allergic
reactions) to the chemical constituents of polysulfides.
Silicones
Silicones represent a new class of impression materials designed to overcome the
drawbacks of polysulfides. They can be further categorized into condensation and
addition silicones.
Condensation Silicones Properties:
•
Excellent fidelity for fluid forms, decreasing with increased consistency
•
Dimensional stability: undergo significant shrinkage after setting, 0.60% for putty
and 0.38% for fluid (greater than polysulfides)
•
Model pouring should be done rapidly, within 60 minutes
•
Pleasant taste and odour
•
Shelf life of 12 months
•
Hydrophobic materials
Addition Silicones Presentation:
They are presented as two-paste systems (base and accelerator) in five consistency
variants: putty, high, medium, fluid, and very fluid.
Properties:
•
Hydrophobic (though hydrophilic variants are also available)
•
Excellent fidelity for fluid forms, decreasing with increased consistency
•
Excellent dimensional stability (0.05% in 24 hours, the lowest among all elastic
materials)
•
Good tear resistance
•
Models can be poured up to 7 days, thanks to their outstanding stability and ease
of pouring
•
Perfect models without air bubbles in hydrophilic ones
•
Pleasant color, odour, and taste
•
Shelf life of 24 months
•
Higher cost.
Indications: These materials are indicated for all types of impression of prosthetic fields
for fixed prostheses, functional impression of partially or totally edentulous prosthetic
fields.
Contraindications:
•
Individuals with intolerance or allergic reactions to some chemical components of
the bases or accelerators of polysulfides.
Polyethers
Polyethers are presented as two-paste systems (base and accelerator), with the
base tube having a much larger orifice than the accelerator tube (an 8:1 ratio) and in two
consistency variants: low and high.
Properties:
•
Hydrophilic materials
•
High and low consistency
•
Very good dimensional stability with 0.12% contraction at 24 hours
•
Good fidelity
•
Removal from the field is more challenging as they become harder and less flexible
after setting
•
Models can be poured up to 7 days
•
Shelf life of 24 months
•
These materials cannot be exposed to water as they have high absorption capacity
and deform easily.
Impression Techniques in Fixed Prosthodontics
The classification of impression procedures for the prosthetic field in fixed prosthodontics
is based on the working steps and is divided into two categories:
1. Single-step (monophase)
2. Two-step (biphasic)
They are further categorized based on the number of components used into:
- monocomponent impressions.
- bicomponent impressions.
In the specialized literature, the following nomenclature for the classification of
impression techniques (Witz 1977) has been established:
Unimaxillar Impression:
1. Conventional or single-step impression
2. Two-step impression
3. Wash impression (two-phase)
4. Double-mix impression
5. Compound impression (sandwich)
6. Impression for FPD (Fixed Partial Denture)
Bimaxillar Impression:
•
Single-unit impression with thermoplastic or synthetic elastomers in a copper ring.
•
Bimaxillary impression with thermoplastic material and synthetic elastomers or with
synthetic elastomers paste and fluid in a special spoon.
For all elastomeric impressions, gingival sulcus preparation is required.
The technique of using addition silicones for a single-step impression with two different
material consistencies is illustrated in the images below.
Single-Step Impression (Monophase):
Indications:
•
Impressions of antagonistic arches
•
Preliminary impressions for making models on which individual trays are
fabricated.
Final Impressions with Synthetic Elastomers.
Monophase impressions can be made using:
•
Standard trays - irreversible hydrocolloids
•
Individual trays - synthetic elastomers
•
Special trays - reversible hydrocolloids
In a monophase impression, the chosen impression material is placed in a universal
tray and positioned in the prosthetic field. This impression is used to record the
antagonistic teeth and is typically made using irreversible hydrocolloids. For all
impressions using synthetic elastomers, gingival retraction is necessary.
Two-Step Impression:
After gingival retraction, elastomeric fluid is injected onto the prepared tooth and
into the gingival sulcus. In the second step, the prepared solid silicone, along with the
catalyst, is placed in a universal tray and positioned in the prosthetic field to encase the
fluid silicone.
This category can also include injection impression techniques. The impression is
obtained in two phases. In the first phase, the solid elastomer (putty) is prepared and
placed in a universal tray equipped with efficient retention systems (2mm holes), and it is
placed in the prosthetic field. After the material sets, the impression is removed from the
prosthetic field. Gingival sulcus retraction is performed between the two phases of
impression making.
The impression created by the putty elastomer is prepared as follows: the surface
is washed under a stream of water, dried with an air jet from the dental unit, and any
excess material is removed from the retentive regions. Triangular grooves (bounded by 2
walls) are cut at the level of the vestibular and oral (tooth) faces, which continue the
vestibular and palatal or lingual side (inferior). The purpose of these grooves is to allow
the excess fluid silicone to flow out and ensure proper reseating of the impression on the
prosthetic field. The presence of grooves prevents deformation of the initial impression
due to overpressure. An alternative to this technique involves reducing the size of the tray
during impression making when the material is still pliable.
In the second phase, fluid silicone(light body) is prepared and introduced into a
syringe for injection into the gingival sulcus, onto the prepared tooth, neighbouring teeth,
and into the impressions made in the first phase using the putty silicon. The tray
containing the impression and fluid elastomer is repositioned in the oral cavity on the
prosthetic field in the same position. After setting (2-4 minutes), the impression is
removed, washed, and dried. Examination of the impression shows that the fluid material,
which has a different color than the putty consistency material, delineates the boundaries
of the abutment preparation and the depths of the sulci. Each edentulous space or gap is
well-defined by a ring-like prominence that extends 0.5-1 mm beyond the impression
surface into the gingival sulcus. Between the abutment impression and the adjacent teeth,
mesial and distal, a wall with thickness indicates the space created for the future
prosthetic restoration, and the inclined parts of the impressions show the negative relief
of the occlusal surfaces.
The material used for recording details can detach from the putty material, if the surface
of the initial impression has not been thoroughly dried - this is a possible defect that
necessitates repeating the impression from phase II.
Advantages of Conventional Impressions:
•
The technique is well-known and widely accepted.
•
Most dentists are reluctant to adopt new concepts once they are accustomed to
the traditional technique.
•
The equipment is simple, and the technique is relatively easy to learn.
•
Cost varies from low to moderate.
•
The accuracy of impressions using addition silicones and poly-ethers is
recognized.
Disadvantages of Conventional Impressions:
•
Conventional impressions can be messy, leaving material residues on patients'
skin, mucous membranes, and between their teeth, which must be removed.
Material residues can scatter throughout the dental office, on gloves, floors,
instruments, etc.
•
Discomfort for patients, with some experiencing a heightened sense of nausea.
•
Errors due to the incorporation of air bubbles and debris can lead to inaccuracies
in the model.
•
Inventory management for impression trays and materials.
•
Additional costs for courier services, sending models to the lab, etc.
Digital Impressions
The digital era necessitates a transition from conventional to digital impressions.
Will digital impressions improve and simplify the impression-taking process? Will they
benefit patients? Will the cost of digital impressions be comparable to conventional
ones?
An estimated 334 million impressions are taken worldwide annually, with 55 million in
the USA alone. Among these, 59% are considered inadequate.
For both conventional and digital techniques, precise tooth preparation is
essential. Digital impressions do not tolerate approximations. Gingival groove
preparation is just as crucial as in conventional impressions.
Advantages and Disadvantages of Digital Impressions:
1. The technique is not familiar to all dentists and convincing some that it is a better
method can be challenging.
2. Complexity - the equipment is sophisticated, although it has simplified
considerably in recent times. Training and instruction are required to master the
technique.
3. Equipment costs are high, but after amortization, it becomes more cost-effective
than conventional impressions.
4. Comparative studies on precision show some similarity between digital and
conventional impressions. However, long-term clinical studies are needed to
determine if these systems are superior in terms of restoration accuracy.
5. Simplicity becomes like conventional impressions after mastering and deepening
the technique.
6. Eliminates office "mess" (additional waste).
7. Eliminates patient discomfort.
8. No risk of inaccuracies due to the incorporation of air bubbles. However, attention
must be paid when recording data to avoid artifacts caused by saliva, debris in
the oral cavity, or gingival margins.
9. No need to store or acquire trays and impression materials.
10. Eliminates the risk of contamination and the need for impression disinfection.
11. Eliminates the need for long-term model storage.
Introduction to CAD/CAM Technology in Dentistry:
The first attempts to apply CAD/CAM technology in dentistry began in the 1970s.
Young and Altschuler introduced the idea of using optical instrumentation to develop a
layered intraoral surface map in 1977.
Francois Duret conceptualized how digital technology used in industry could be
adapted to dentistry to obtain digital impressions. Duret's innovative idea dates to 1970,
which he further developed in his doctoral thesis completed in 1972. The principle
involves using a laser beam to obtain a digital impression based on the biphasic
profilometry principle, which can then be transferred to a computerized design and
manufacturing system. This is essentially the concept of CAD/CAM applied to the
fabrication of various dental restorations. At the time, his enthusiasm was not widely
shared.
The first functional 3D intraoral camera for capturing intraoral images was called
RedCam (using infrared laser radiation as a light source, later replaced by BlueCam –
blue laser radiation) (Mormann et al., 1987). Today, an optical interference-free intraoral
camera that provides a real-time, high-definition, color image, called Primescan, is the
latest addition to the CEREC family and is among the top intraoral scanners.
Conventional vs. Digital Impressions:
Why use digital impressions? The answer is the same as for why we use cell
phones, GPS, computers, etc. These technologies increase our efficiency and the
quality of medical care.
Digital impressions make the lives of dentists easier, better, more efficient, and
increase patient satisfaction (Seelbach et al., 2013; Lee & Galucci, 2013).
What can we evaluate with a conventional impression? Margin quality, whether it
captured the entire area of interest, but the quality of the preparation can only be
assessed after the model is poured. Statistically, over 50% of conventional impressions
do not record the entire margin of the preparations (Christensen, 2005).
With digital impressions, it is possible to evaluate the magnified image of the
preparation in real-time on the monitor screen. Deficiencies that can be addressed on
the spot, while the patient is still in the chair, such as the degree of preparation
inclination, margin quality, retentive features, and interocclusal space, are highlighted
using various color codes, with micron precision.
Digital impressions eliminate the risk of material distortion, porosity, and tensile forces
that can lead to distortion in conventional impressions. Research shows that the
accuracy and precision of digital impressions are like conventional ones (Leu, 2008;
Holmes, 1898; Endel & Mehl, 2011, 2013, 2015; Patzelt, 2014). Additionally, because
digital impressions do not require the pouring of a model, there is no risk of gypsum
expansion.
Models produced from digital impressions are either 3D printed or milled from a
block of material. CAD/CAM-produced models have acceptable clinical accuracy (50
microns) (Endel & Mehl, 2011; Patzelt, 2014).
Digital impressions increase the efficiency and profitability of dental practices,
being faster than conventional ones (Patzelt, 2014). Retaking a digital impression takes
seconds and costs nothing. It eliminates the need for disinfection and impression
storage. Only the tip (wand) of the scanner is autoclaved for each patient.
Despite these advantages, there is still room for improvement, and
manufacturers introduce new enhancements to digital impression systems each year. In
the last 20 years, intraoral scanning devices have evolved significantly, to the point
where conventional impression-taking techniques are predicted to become obsolete in
the near future.
CHAPTER 6. PROVISIONAL FIXED PARTIAL DENTAL PROSTHESES
Provisional Fixed Prosthetic Restorations (PFPR) represent an important
intermediate stage in the process of obtaining the definitive prosthetic restoration,
designed to improve the aesthetics and enhance the function of the temporary dental
prosthesis over a limited period of time (Glossary of Prosthodontic Terms). The term
"provisional" emphasizes the temporary nature of the restoration, which is also referred
to in the literature as a transitional, interim, or temporary restoration.
In the construction of PFPR, the clinician must focus on both protecting and
stabilizing dental structures and achieving the most accurate restoration of aesthetic,
masticatory, and phonetic functions. The ultimate success of fixed prosthetic
restorations and collaboration with the patient depend on the quality standards of this
treatment phase.
In the treatment of partial edentulism with fixed prostheses, PFPR must fulfil
several objectives, including:
•
Diagnosis clarification.
•
Refinement of the treatment plan.
•
Patient's motivation for the treatment plan.
•
Communication of information to the laboratory.
•
Healing of remaining tissues.
•
Establishing occlusal and VDO (vertical dimension of occlusion)
•
Restoration and evaluation of phonetics, mastication, and facial
plans.
aesthetics.
•
Prevention of dental migrations.
•
Assessment of the parallelism of prepared teeth.
Depending on the intended and actual duration, two categories can be
distinguished:
•
Short-term PFPR.
•
Long-term PFPR, which can be maintained in the prosthetic field for
up to 2 years.
The concept of long-term provisional prosthetic restoration is relatively
recent and refers to those temporary fixed prostheses that need to be maintained in the
arch for several months, even 1-2 years, to allow for the consolidation of orthodontic,
surgical, or implant prosthodontic outcomes.
6.1. Objectives of PFPR
PFPR must fulfil a series of objectives, including:
•
Pulp protection.
•
Enamel surface protection.
•
Marginal periodontal protection.
•
Ensuring dimensional stability of the lower face.
•
Maintaining occlusal function.
•
Accessibility for proper hygiene.
•
Ensuring resistance and retention.
•
Ensuring appropriate aesthetics.
•
Prefiguring or supporting subsequent treatment stages.
6.1.1. Protection of pulp vitality from mechanical, thermal, chemical, and bacterial
factors is achieved through:
-
Proper adaptation of PFPR to the abutment.
-
Covering the terminal area of the preparation with PFPR.
-
Preventing marginal saliva infiltration.
-
Choosing a thermally insulating material for PFPR construction.
6.1.2. Protection of enamel surfaces: PFPR prevents the fracture of the prepared
abutment, or the edges of the preparation exposed to masticatory forces.
6.1.3. Marginal periodontal protection is achieved through proper PFPR
conformation. To prevent gingival hypertrophy/inflammation, PFPR over contouring
should be avoided. PFPR over contouring can cause gingival retractions. If it is a fixed
provisional prosthesis with multiple elements (a provisional bridge), correct embrasures
and hygiene spaces must be ensured. A properly designed and executed provisional
restoration at the cervical level provides optimal conditions for impression of the
terminal area and gingival sulcus.
6.1.4. Positional stability: PFPR prevents dental migrations of the abutments and
antagonistic teeth. By preparing the abutments, the contact area with neighbouring and
antagonistic teeth is lost, and the role of PFPR is to maintain positional stability by
restoring occlusion and interproximal contact morphology, thus preventing vertical and
horizontal migrations of abutments (mesialization, distalization), as well as vertical
migrations of antagonistic teeth. These position changes result in mal-adaptations of
definitive restorations, the need for subsequent adjustments, and sometimes the need
to remake the definitive restoration.
6.1.5. Maintenance of occlusal function is achieved by:
-
Restoring contacts and relationships with the opposing arch.
-
Preserving occlusal stops.
-
The ability to test a new VDO (vertical dimension of occlusion).
6.1.6. Maintaining proper hygiene involves creating PFPR with open embrasures,
a suitable design that allows the patient to establish a correct hygiene program, which
will later be continued for the hygiene of future definitive fixed prosthetic restorations.
6.1.7. Ensuring resistance and retention. To prevent PFPR from fracturing under
the action of masticatory forces, the clinician must pay special attention to the choice of
material for construction and ensure optimal thickness and adequate retention at the
abutment level.
6.1.8. Physiognomic function is of paramount importance in fixed prosthodontic
treatment, especially in the frontal and premolar regions. The provisional prosthesis can
prefigure the shape, color, and alignment of the future prosthetic restoration, playing a
crucial role when effective communication with the patient is needed to modify the smile
design.
6.1.9. By prefiguring or supporting subsequent treatment stages, PFPR allows for
control of the preparations. Thus, it can be checked whether the preparation is sufficient
both axially and occlusally, whether the abutments present retentive features, and
whether they are parallel.
The advantages of provisional prostheses include:
•
Providing physical and psychological comfort to the patient.
•
Educating the patient to maintain proper oral hygiene, necessary for
future definitive fixed prosthetic restorations.
•
Refining the treatment plan.
•
Facilitating communication with the dental laboratory.
•
Correctly shaping the gingival tissue in the terminal area of the
preparation, allowing for precise impression.
The disadvantages of provisional prostheses include:
•
additional working time.
•
associated costs.
•
decementation or fracture of PFPR.
•
if the aesthetics of PFPR differ significantly from those of the
definitive restoration, patients may have difficulty accepting the final prosthetic
treatment.
•
allergic reactions to PFPR materials.
•
reversible or irreversible pulp inflammation following certain
fabrication techniques (Bratu).
6.2. Classification of Provisional Restorations
Provisional restorations can be classified based on their method of fabrication.
Industrially obtained ones are only suitable for single-tooth provisional restorations and
include aluminium crowns, anatomically contoured metal crowns, celluloid formers, and
prefabricated polycarbonate crowns. Individually customized provisional restorations,
made in the dental office or dental laboratory, can be crafted from a wide range of
polymers and composite resins using various technical methods.
Another classification of provisional restorations pertains to the fabrication
technique, which can be either direct, performed in the dental office by the dentist
directly on the patient's prosthodontic field, or indirect, where provisional restorations
are created on a gypsum model in the dental laboratory.
Depending on the number of teeth replaced, provisional restorations can be
classified into:
1.
2.
Single-tooth provisional restorations:
•
Temporary crowns - full or partial coverage.
•
Temporary inlays.
•
Temporary core-build-ups.
•
Temporary veneers.
Partial fixed provisional prostheses:
•
Emergency prostheses - mainly used in the anterior region,
post-extraction, or post-traumatic.
•
Protective prostheses - for vital abutment teeth.
•
Testing prostheses - serving as a guide to check occlusal,
physiognomic, and phonetic functions of the future definitive restoration.
•
Waiting prostheses - belonging to the long-term type:
•
Space maintainers.
3.
•
Periodontal immobilization systems.
•
Post-surgical fixed partial prostheses.
•
Post-implant fixed partial prostheses.
•
Post-orthodontic fixed partial prostheses.
•
Socio-economic compromise fixed partial prostheses.
Temporary removable partial prostheses (TRPP):
-
Emergency TRPP - after multiple tooth extractions or damage
to existing TRPP.
-
Testing TRPP - physiognomic, occlusal, phonatory.
-
Waiting TRPP - for delaying definitive treatment.
-
TRPP with occlusal splint - if occlusal splint application is
necessary for protection against parafunctional habits.
-
Space maintainers TRPP.
-
Post-surgical TRPP - after oral and maxillofacial surgery.
-
Socio-economic compromise TRPP.
a.
b.
Fig. 6.1. Testing provisional restoration for veneers (a. initial situation, b.
provisional after wax-up).
6.3. Materials for Fabricating PFPR
Currently, there are numerous materials designed for provisional restorations,
and they must meet the following criteria:
•
Biocompatibility (non-toxic and non-allergenic).
•
Compatibility with other materials (such as provisional cements).
•
Dimensional stability.
•
Low thermal conductivity.
•
Ease of preparation and manipulation.
•
Acceptance by the patient (non-irritating).
•
Easy adjustability and optimization.
•
Cost-effectiveness.
Polymers intended for PFPR can be classified as follows:
a. Self-polymerizing methyl or ethyl methacrylate-based resins.
b. Thermally polymerizing resins for PFPR (longer duration).
c. Photopolymerizing composite diacrylic resins.
d. Dual-cured composite diacrylic resins
e. Polymethyl methacrylate (PMMA), available in pre-polymerized blocks for
CAD/CAM technology.
Polymers and composite materials can be grouped as follows: auto- or thermal
polymerizing acrylic resins, polycarbonate resins, self-polymerizing epiminic resins,
composite diacrylic resins, acetal resins, auto-ligth-polymerizing/dual-cured resins, and
glass fiber-reinforced resins.
MATERIAL
Advantages
Disadvantages
Metal
prefabricated, no need for index
Requires significant adjusments, poor
aesthetics
Polycarbonate prefabricated
prefabricated, no need for index
crowns
Methyl methacrylate
Ethyl-methacrylate
Bis -acryl
Major adjustments needed for marginal fit,
contact points and occlusion
Good strength and aesthetics, easy to
Strong exothermic reaction, contraction,
repair, multiple units, last long
require shaping, laboratory involved
Less exothermic reaction than PMMA, easy
Less wear-resistant than PMMA, contraction,
to repair
shorter lifespan
The most popular material (available in
High costs, requires index, difficult to line, not
syringes), significantly reduces exothermic
suitable for long-span bridges
reaction, no unpleasant odor, can be used
for long term ususe, easy to handle
UDMA
Photopolymerizable, good mechanical
High costs, requires index, exothermic
properties, good aesthetics, easier to line
reaction due to photopolymerization
than bis-acryl
Diacrylic resins
Excellent aesthetics, ideal for temporary
High costs, time-consuming
veneers, can be used with or without
shaping, no need for temporary cement
Modified composites
Low viscosity, ideal for provisional inlays, no
The material is less resistant, poor
need for index, temporary cement
interproximal and occlusal contacts, difficult to
remove from retentive areas
TYPE
Commercial
name
Manufacturer
Advantages
Disadvantages
Methylmetaacrylate
Alike Jet
GC America
Lang Dental
- Good marginal adaptation
- Good tranversal strength
- Good polishablility
-Durability
Ethylmetaacrylate
Snap
Parkell
-good polishability
-minimal exothermic
reaction
-low volumetric contraction
-chromatic stability
- strong exothermic
reaction
-low abrasion resistance
-pulpal toxicity due to
residual monomer
-high volumetric
contraction
-self-polymerizing
-low hardness
-low transversal strength
-low durability
-low fracture resistance
-self-polymerizing
Vinyl-ethylmethacrylate
Trim II
Bosworth
-good polishability
-minimal exotgermic
reaction
-good abrasion resistance
-flexibility
-chromatic stability
Methyl-ethylmetaacrylate
Unifast-LC
GC America
-good marginal adaptation
-good transversal strength
-good polishability
-durability
-dual polymerization
BIS-acryl
composite
Luxatemp
Turbotemp 2
Protemp II
Temphase
Goregeous
Temp
Zenith-DMG
Oanvi lle
Engineering
3M- ESPE
Kerr
DenMat
-good marginal adaptation
-minimal exothermic
reaction
-good abrasion resistance
-good transverse strength
-low volumetric contraction
-dual polymerization
-excellent polishability
Compozit BISGMA
TempSpan
Pentron
Clinical Tech
-good marginal adaptation
-good polishability
-very low exothermic
reaction
-good abrasion resistance
-good transverse strength
-very low volumetric
contraction
-thin layer of unpolymerized
oxygen
-good chromatic stability
-can be repaired with flow
or hybrid composite
-low hardness
-low transversal strength
-self-polymerizing
-low fracture resistance
-low surface hardness
-low chromatic stability
-fragility
-thick layer of
unpolymerized oxygen
-higher cost compared to
methacrylates
-difficulty in repair
-limited color selection
The choice of the appropriate material for provisional fixed prosthetic restorations
depends on several factors, including the fabrication technique, the extent of
edentulism, the duration of PFPR usage, and the equipment available in the clinic or
laboratory.
1.
Acrylic Resins:
•
Self-curing and heat-curing types
-
Used in both direct and indirect techniques
-
Bicomponent system (powder and liquid)
-
Exothermic polymerization reaction, which can be harmful to
dental pulp
-
Suitable for extensive PFPRs using the indirect technique
-
Heat-cured acrylic resins:
§
High aesthetic and mechanical qualities, chromatic
stability, suitable for long-term PFPRs.
2.
Polycarbonate Resins:
-
Granules of thermoplastic, reversible, injectable polymers
-
Used in the direct technique
-
Suitable for anterior teeth PFPRs
-
Superior properties compared to acrylic resins, autoclavable
-
Requires special injection equipment if fabricated in the clinic
or available as prefabricated polycarbonate crowns.
3.
Epimine Resins:
-
Available in a self-polymerizing, two-component system (base
and catalyst)
-
Suitable for PFPRs made using the direct technique due to
reduced toxicity and minimal exothermic reaction
-
Disadvantages include reduced chromatic stability, marginal
adaptation, and mediocre wear resistance.
4.
Composite Diacrylic Resins:
-
Photopolymerizable
-
Exhibit high values of chromatic, mechanical, and chemical
resistance, with minimal contraction during polymerization
-
Suitable for both direct and indirect techniques for anterior
and support zone PFPRs
5.
High cost is a disadvantage.
Acetal Resins:
-
Processed through thermos-injection
-
Outstanding characteristics: aesthetics, strength, resilience,
biocompatibility, dimensional stability, easy processing.
6.
Dual Resins:
-
self-photopolymerizable
-
Initial polymerization begins during mixing of the two
components, transforming the material into an elastic phase that remains
until final photopolymerization
-
Highest modulus of elasticity and remarkable fracture
resistance.
7.
Glass Fiber-Reinforced Resins:
-
New materials promoted by the Tragis-Vectris system
-
Suitable for long-term PFPRs (2-5 years)
-
Advantages include optimal aesthetics, minimal technical
errors, excellent marginal adaptation, and resistance to masticatory forces.
8.
Composite Bis-Acryl Resins:
-
Presented in an auto-mixable system
-
Suitable for long-term PFPRs, both single- and multi-toothed,
in anterior and posterior regions, inlays, onlays, and prefabricated
composite crowns
-
Advantages include excellent aesthetics, faithful marginal
adaptation, easy cleaning, easy handling, superior mechanical properties,
minimal contraction, and low setting temperature.
Fig. 6.2. Bis-acryl resin, a two-component paste-paste system in a cartridge.
The development in the field of nanotechnology has led to changes
in the field of RPP, which has expanded by introducing prefabricated
composite crowns for single-unit RPP, creating a hybrid between the
advantageous results of auto mixable materials (aesthetics, adaptation,
fidelity) and prefabricated crowns (material, time, and experience savings).
Prefabricated RPP made of composite initially comes in a malleable state,
like wax, and can be easily adapted and shaped to the dental preparation.
Photopolymerization defines a resilient, finishable, polishable temporary
crown.
Advantages: optimal aesthetics, reduced working time,
reduced costs (no need for impressions).
4. Techniques for obtaining prefabricated crowns
4.1 Prefabricated crowns
• Materials used for prefabricated crowns:
- polycarbonate.
- aluminium.
- tin-silver.
- nickel-chrome;
- composite resins.
4.1.1 Polycarbonate prefabricated crowns:
- Suitable for both anterior and posterior regions;
- Objectives: gingival protection, maintenance of occlusal relationships, restoration of
contact area with adjacent teeth;
- Working stages include: - color selection;
- adaptation of the crown to the prepared abutment;
- lining with self-polymerizing acrylic resin;
- verification, adjustment, and polishing of the margins
- verification of occlusal plane and occlusal stops;
- checking the adaptation of the crown to the abutment; provisional fixation of
the crown.
- Working technique - for crown selection, the clinician determines the mesio-distal
diameter of the tooth to be prepared, either intraorally or on a model - after preparing
the abutment, the provisional crown will be adapted in relation to the adjacent teeth.
If the crown is too long, it will be shortened at the cervical level using a handpiecemounted bur, following the gingival contour of the abutment. In case difficulties arise
during the insertion of the provisional crown, it will be narrowed mesio-distally
without compromising the proximal contacts with adjacent teeth.
- Lining the temporary crown with self-curing acrylic resin will provide optimal
retention and adaptation.
- Prior to lining, the abutment and adjacent tissues are coated with Vaseline.
- The acrylic resin is prepared in a dappen dish and the resulting resin paste is
loaded into the polycarbonate crown and applied onto the abutment under pressure,
to ensure registration of the gingival area.
-pressure is maintained on the temporary crown until the resin regains its
shape memory, visible in the cervical area, after which the clinician begins mobilizing
the crown and repositioning it on the abutment
- before final setting, the crown should be left in lukewarm water for 5 minutes
for complete polymerization
- if the new temporary crown fits perfectly, it will be processed, finished, and
temporarily fixed
4.1.2. Prefabricated metal crowns:
- indicated for posterior regions;
- similar objectives to polycarbonate temporary crowns;
- advantages: easy adaptability, well tolerated at the gingival level
4.2. Direct fabrication technique for temporary crowns:
- eliminates laboratory procedures;
- advantages: time and cost savings;
- disadvantages: risk of tissue trauma during polymerization (due to
temperature increase), inadequate marginal adaptation;
- indications: single or multiple unit temporary crowns with a reduced number
of teeth
4.2.1. Direct fabrication technique using custom trays
Custom trays are auxiliary means for fabricating temporary crowns that
reproduce the negative shape of the teeth before they are prepared or the modified
tooth shapes with wax on a gypsum model (wax-up)
Types of trays: prefabricated industrial trays and trays made in the dental
office
4.2.1.1. - High-consistency silicone impression material (to be easily trimmed
into the desired shape) is the most suitable direct tray:
- advantages: flexibility, low cost, easy trimming;
- disadvantages: sometimes difficult to reproduce surface details of the teeth.
Fig. 6. Silicon index for creating provisional restoration.
4.2.1.2 - Thermoplastic films - made of propylene acetate or cellulose, with a
thickness of 0.5mm - are heated and adapted to the gypsum model under vacuum
- advantages: the transparency of the film provides constant visual control
during the working time, ensures correct positioning of the conformer on the
prosthetic field, and reduces working time.
Fig. 7. Conformer obtained through thermo-vacuum forming.
- the conformers will be perforated with a probe, towards the outside, in order
to allow the RPP material to vent without creating any depletion in the thickness of
the crown.
4.2.2. The steps for direct technique in the fabrication of RPD are as follows:
1. obtaining a conforming structure, in the form of an impression;
2. relieving the conforming structure to ensure optimal adaptation;
3. creating grooves on the vestibular and oral surfaces of the impression to
guide excess material flow out of the conforming structure;
4. removing excess material after polymerization reaction;
5. when using thermoplastic foil conforming structures,
photopolymerizable/dual resins can be chosen for RPD;
6. conforming the gingival margins;
7. verifying adaptation on the prosthetic field and occlusal plane;
8. finishing and polishing the RPD;
9. temporary fixation.
4.2.2.1. Fabrication of RPD through direct technique in the conforming
impression
- a high-consistency silicone-based impression material will be used to create
the conforming impression - the prosthetic field will be impressed using a standard
tray in a single-step impression technique (with two consistency types)
- after removing the impression from the oral cavity, it will be trimmed to
remove excess material for easy reinsertion.
-the clinician prepares the abutment and after its completion, checks the
adaptation of the conformer
- Both the preparation and the adjacent area are lubricated with Vaseline
- The chosen material for making the RPP is applied with the help of a
dispenser and a nozzle, ready homogenized, inside the conformer at the level of the
area to be restored
- The conformer is applied to the prosthetic field and polymerization is awaited
- If the RPP is over-contoured, the margins will be reduced by finishing
- If the RPP has defects and gaps, they will be corrected with flowable
composite
- If the adaptation of the RPP is adequate, it will be finished with burs,
brushes, and finishing paste.
Fig. 8. Inserting the provisional restoration material into the silicone key.
4.3. The combined technique for the fabrication of RPD
- consists of creating a RPD in the laboratory, based on the diagnostic model.
This restoration is thin and not adapted to abutments, therefore it requires lining in
the oral cavity.
The advantages are: - reduced working time for the clinician;
- increased biocompatibility due to the reduced amount of heat released
intraoral;
3.1. The steps in the combined technique are:
1. taking an impression of the initial situation in a previous appointment;
2. removing the material corresponding to the gingival groove from the
impression, thus widening the area of the cervical margin;
3. applying the material for the RPD inside the impression, on the teeth to be
restored;
4. positioning the impression on the prosthesis field, on the prepared teeth;
5. polymerizing the impression;
6. removing the excess material;
7. polishing and finishing the RPD;
8. temporarily fixing the RPD.
Fig. 9. Proper adaptation and contouring of RPP (Removable Partial Denture) margins.
4.4. Indirect technique for making RPD
- obtained exclusively outside the oral cavity, without risks for the patient
- after preparing the abutments, the prosthetic field is imprinted
- a working model is poured - RPD is fabricated on the model.
- Advantages: - abutments and marginal tissues are not exposed to
polymerization
- increased biocompatibility
- optimal marginal adaptation (Bratu)
- clinical steps: 1. Determining the color;
2. Tooth preparation;
3. Choosing the impression tray;
4. Highlighting the terminal area of the preparation;
5. Impressing the prosthetic field;
6. Pouring the model and performing laboratory steps;
7. RPD is checked in the oral cavity - proximal contact areas;
- contour and possible surface defects;
- occlusal and marginal adaptation.
8. Defects will be corrected by resin augmentation;
9. Provisional fixation.
In order to visualize the aesthetic aspect of the future final prosthetic
restoration and to improve clinician-patient communication, modern prosthodontics
introduces new techniques:
• Computer simulations
• Wax modelling on a wax-up model
• Intraoral mock-up modelling
a. Computer simulations:
- consist of the need for digital software
-hardware tools through which the user can create the future virtual aesthetic
aspect
- necessary tools:
- cameras and photo and video scanners
- monitors and tablets
- specialized programs that can communicate with CAD-CAM technologies
have raised the standards of classical prosthodontics.
Advantages are: - speed, efficiency
- Disadvantages: - high costs for equipment,
- sometimes the inability to accurately reproduce the virtual design in the oral
cavity (Ionas)
b. Wax modelling on a wax-up model:
- the future RPD will be modelled in wax on the study model
- indications: - choosing the treatment plan;
- possibility of effective communication with the patient and presentation of
the treatment plan.
- making the silicone key.
- advantages: - reduced time due to technical steps performed in the dental
laboratory
- the patient can visualize and suggest modifications regarding the aspect of
the final restoration
- perfect cervical adaptation
- high aesthetics
- disadvantages: - requires two treatment sessions
- dental laboratory costs
- Steps of fabrication of RPD modelled in wax on the wax-up model
- the prosthetic field of the initial situation is impressed, with one session
before starting the prosthetic treatment
- based on this impression, a diagnostic model (wax-up)
-the technician shapes the wax model based on the diagnostic model, and
then duplicates the diagnostic model.
-The technician creates a conformer based on the duplicated model.
- Using the duplicated model, the technician prepares the future abutments.
-The indirect classic technique is used to create the RPD on the abutments
of the duplicated model.
-Once the prosthodontist completes the abutment preparation, they will check
the fit of the RPD received from the laboratory (which may not have an optimal fit
with the prepared teeth). If adjustments are necessary, the RPD will be optimized.
-The preparations and adjacent tissues are lubricated with petroleum jelly,
and the clinician will line the RPD using a direct technique.
- The RPD is then finished and temporarily fixed.
c. Intraoral Mock-up:
- It involves modifying the physiognomy directly in the oral cavity by
applying composite material to the dental structures without using an
adhesive system.
- Indications:
- Single-tooth structures in the frontal or lateral area (Ardu).
- Advantages:- Rapid presentation of the result.
- Requires only one session.
- Disadvantages:- Requires an experienced clinician for the shaping.
- Time-consuming treatment session (Ionas).
Conclusion:
With numerous technological options available for RPD fabrication, it is
the clinician's duty to select the appropriate type of restoration for each
individual case.
5. Fixation of RPD
During the provisional fixation period, the following are monitored:
• Proximal, occlusal, and alveolar ridge relationships
• Esthetics
• Soft tissue behaviour
• Oral hygiene
Qualities of materials used for cementing RPD:
• Biocompatibility
• Optimal marginal closure
• Easy preparation, adequate working and setting time
• Chemical compatibility with the polymer
• Mechanical strength
• Easy removal of excess material
Removal of RPD should be easy, without affecting soft and hard tissues and without
compromising the restoration.
Stages of cementation:
• Isolation of the prosthetic field
• Preparation of the provisional fixation material
• Loading of the RPD with the fixation material
• Insertion of the RPD into the oral cavity, verification of correct positioning
•Removal of excess cement
CHAPTER 7. MODERN METHODS OF CHOOSING, COMMUNICATING AND
REPRODUCING COLOR IN DENTAL PROSTHETICS
The major advantages of the computerized methods of choosing and
communicating the color are primarily objectivity and precision and can be concretized as
follows:
- they are not influenced by the surrounding environment.
- they are not influenced by light;
- the results are reproducible.
The three large classes of devices for measuring color are:
- RGB devices,
- spectrophotometers
- colorimeters.
Devices that capture image information (for red, blue, and green) to create a
color image are called RGB devices. Most digital cameras and video cameras belong to
this category. Most RGB devices are based on the most basic electronic color
determination system, but they show a certain degree of subjectivity because they cannot
monitor certain variables.
Color is determined using data captured by the digital camera. The accuracy of
the information obtained with the help of these RGB devices is questionable since it is not
based on an objective measurement. These systems are useful as a starting point for the
information that will be transmitted to the dental laboratory. One such RGB system is
Shade Scan by Cynovad (Fig.)
With the help of this device, the appearance and color of the teeth can be
perceived in a similar way to the human eye, but with the accuracy and consistency of a
computer. During a few minutes, the image of the tooth is captured by scanning and will
be sent to the laboratory. The software of this system records the data related to the three
color parameters and elaborates the chromatic map of the tooth.
The Cynovad Shade Scan system is an RGB device that records the chromatic
characteristics of the teeth
The times of using this device are: inserting the Shade Disk in the upper part of
the part (Fig.4.6), applying the protective device and self-calibration. Then the screen of
this scanner will be applied in contact and parallel to the surface of the tooth, after which
the image will be captured, which will be transmitted through the Shade - Port system to
the computer, where the image will be analyzed through the Shade Scan software (Fig.
4.7 ).
Fig.4.6. Inserarea discului Shade
Fig.4.7. Utilizarea soft-ului
pentru alegerea Disk
culorii şi întocmirea hărţii
cromatice
Digi Color is a system developed by O'Brien Dental Lab, which presents a
complex program with multiple facets, which combines digital photography, color
selection with color keys and photo analysis with the help of software that will be able to
prepare a color map useful for the dental laboratory dental technique (Fig.4.16). With the
help of a high-resolution digital camera, a photo is taken that will be printed on a special
paper and sent to the dental laboratory. After the color analysis, the software will develop
the chromatic map, through which the photographic image is obtained by color sections,
giving the technician clear information regarding the choice of the optimal ceramic color
set for each individual section.
Fig. 4.16. The Digi Color system software analyzes the photographic image and
creates the color map (in the image there is a tooth from the color key)
The "Clear Match" system is a color communication software between the doctor
and the laboratory, which uses mathematical analysis to determine the color of the teeth
in a few seconds. The system requires a computer with the specific software installed and
a digital camera, no other investments are required (Fig. 4.17).
The stages of choosing the color using the Clear Match system are:
1. capturing the image with the digital camera, storing the image in the patient's
file or integrating it into other software (Vipersoft® or Dentrix®);
2. choosing the color by recording the three color parameters H, V, C (hue,
brightness and saturation) through a mathematical analysis system and obtaining a color
map.
3. sending the information to the laboratory via e-mail;
4. comparing the results; the system presenting the possibility of evaluation by
percentage differences of the initial image of the tooth with the one at the end of the
treatment.
Fig. 4.17. The Clear Match system allows the analysis of the color of the entire
surface of the tooth, the creation of the color map and the transmission of information via
electronic mail to the dental laboratory.
Spectrophotometers
The spectrophotometer is a device that consists of 3 main elements: a light
source, the system for transmitting light to the object and receiving the light reflected from
the object, and a spectrophotometer that determines the intensity of the received light as
a function of wavelength.
The Vita Easyshade system has a CPU for spectral data analysis and color
determination to match the classic Vita system Vitapan 3D Master (Fig.4.18.).
It is a portable intraoral spectrophotometer, easy to use. It consists of a base unit
and a handle that connects to the base unit via a fiber optic cable. The handpiece contains
a fiber optic assembly for illuminating and receiving light from the tooth, as well as a
multiple spectrophotometer and a microprocessor for communication with the base unit.
The communication between the handpiece and the base is done via USB. The basic unit
contains a set of lamps, CPU, a fluorescent vacuum display with touch screen system
and a removable calibration system.
There are both RS232 and USB interfaces for connection with external
computers.
The system uses a 20Watt stabilized tungsten halogen bulb, with a color
temperature of 3350 °K and a continuous light source for the entire spectrum. The lamp
requires 15 seconds to warm up and stabilize, and the average life of the lamp is 100
hours.
The Easyshade handpiece contains 3 separate spectrophotometers. One
spectrophotometer continuously monitors the output signal from the lamp during the
calibration and measurement process, and the other two are used to analyse the light
that is reflected by the tooth. Spectrophotometers have separate receiving elements,
located at different distances from the light source, and measure the color of a material
(tooth or ceramic) for different depths.
Fig. 4.18. Vita Easyshade system
For infection control, a disposable polyurethane sleeve is applied over the
handpiece.
The process of determining color is based on comparison. A ceramic block of
known color will be used for calibration. Several determinations are made for calibration:
the first ones are with the lamp in the off position, and the following ones with the lamp in
the on position, to illuminate the calibration block.
The data obtained from the spectrophotometers will be transformed into a
spectral curve (Fig.4.19), which is very useful especially in the research activity.
Fig. 4.19. The data obtained with the help of spectrophotometers are more difficult
to transpose in the daily activity in the offices, but they are extremely useful in the research
activity.
Widespread use of spectrophotometers in dentistry, both in research and in the
clinical field, has been less extensive since the equipment required is expensive and
sophisticated. Until recently, it was difficult to measure tooth color in vivo with the help of
spectrophotometers.
The best research spectrophotometer used is called spherical optics, where the
object is placed inside the apparatus and exposed to light from different directions and
angles. This results in the most accurate spectral analysis of the object. (Fig.4.20).
Spectrophotometers for dental use cannot obtain the same degree of illumination all
around (360 degrees), since the tooth cannot be placed inside the device. The light is
directed onto the surface of the tooth.
Fig. 4.20. A light exposure all around (360 degrees) cannot be obtained
Fig.4.21. For clinical use of in clinical conditions (in offices) only in
spectrophotometers, the best research conditions (15) setting is 45/0 (illumination at 45
degrees and observation at 0 degrees) (15)
There are two settings used in reflectance spectrophotometers: illumination at 0
degrees and observation at 45 degrees (0/45), respectively illumination at 45 degrees
and observation at 0 degrees (45/0). For clinical observation, only the second variant
(45/0) can be used (Fig. 4.21).
A spectrophotometer designed for clinical observation is the SpectroShade from
MHT. (Fig.4.22.) This system uses two digital cameras, connected by optical fiber with a
spectrophotometer that measures the teeth color parameters. The system is based on a
multimodal mechanism, with a dual light source, which illuminates the teeth and allows
translucency and reflectivity to be read. SpectroShade has the ability to display color
results in an advanced graphic (Fig.4.23).
Fig. 4.22. The Spectro Shade spectrophotometer of the MHT company
4.23. The Spectro Shade system offers the possibility to draw up the color map of
the entire tooth quickly and precisely
4.2.3. Colorimeters
Much of the research in the field of dental medicine regarding the color of natural
teeth and ceramic restorations, both in vivo and in vitro, has been done with the help of
colorimeters. They are designed to measure color as perceived by the human eye.
A colorimeter filters light into three or four areas of the visible spectrum to
determine the color of an object, but they are less accurate than spectrophotometers.
A high-performance colorimeter is the X-Rite ShadeVision (Fig. 4.24), which
shows remarkable efficiency, because it stores the data related to the three-color
parameters (hue, saturation and brightness), unlike spectrophotometers that record at
least 16 points of reflectance. A colorimeter can give information about color, similar to
that provided by a spectrophotometer, but simplifying the process, eliminating a lot of data
related to the spectral analysis that is obtained with the help of spectrophotometers, data
that is not necessarily necessary.
The stages of color determination through technological methods as in the case
of traditional methods, the stages of color determination with the help of technological
systems are the following:
• -color analysis;
• - color communication;
• - color interpretation;
• - making the restoration;
• -checking the color of the restoration
Color analysis
Most technological color determination systems use the ΔE of the CIEL*a*b*
system to determine the color difference between the tooth to be restored and a chosen
color. This difference is the smallest distance in the CIEL*a*b* color space, between the
colors that are compared and is determined by the following equation:
ΔE=(ΔL*2+Δ a*2+ Δ b*2)1/2
L* - represents brightness (from white to black);
a*- corresponds to the red-green axis (positive values indicate red, negative values
indicate green);
b*- corresponds to the yellow-blue axis (a positive value indicates yellow, a
negative value indicates blue).
ΔL, Δ a, Δ b, as well as ΔE are graphically represented in a numerical form in the
Shade Vision and ShadeEye system, with the help of the Shade Match digital system.
The SpectroShade system allows changing the chosen color depending on the different
ΔE values, which will increase the accuracy of the initial choice.
With the help of digital analysis, the goal is to obtain the lowest value of ΔE,
which indicates the most accurate determination of the color, in the three areas of the
tooth (gingival, middle, and incisal). This value is not directional, i.e. it does not indicate
whether one color is darker or lighter than another. The ΔL value is the most important
parameter, because the human eye can detect changes in brightness more easily than it
can detect changes in hue.
It has been shown that a value of ΔL less than 2 and a total difference ΔE less
than 4 represents a clinically acceptable color.
Digital analysis is faster and less subjective than conventional methods of color
determination. The color is measured electronically, either with a colorimeter or with a
spectrophotometer, and a color map is drawn up, visually checked, and sent to the
technical laboratory dental.
Color analysis also involves choosing the optimal material for each type of
restoration, because the intrinsic properties of different materials can greatly affect the
perception of the shade of the future restoration.
Color communication
A precise and efficient communication with the dental laboratory is the foundation
of predictable and successful results in the case of aesthetic restorative treatment. With
the help of technological systems, communication becomes much simpler and more
precise, being carried out in electronic format. The images are captured and analysed by
the existing processor in the office, and the information is then sent via electronic mail
directly to the dental laboratory.
It is good that, in addition to the information processed and transmitted in electronic
format, digital color photos can also be sent, which can provide additional data regarding
the appearance of the future restoration.
Interpretation of the color
In the dental laboratory, the technician will analyse the color map and interpret the
photographs before proceeding to fabricate the restoration. The interpretation of data
received via e-mail is subjective and depends on the knowledge and skills of the
technician. It must take into account several factors that can change the perception of the
color of a restoration, such as surface texture, anatomical shape, surface gloss and
fluorescence.
Fabrication of the restoration
When fabricating a restoration, the technician must consider the intrinsic properties
of the materials to obtain both the desired color and the appropriate translucency and
opalescence. The devices that measure the color of the teeth on restricted areas (SM),
help the technician to choose the color for the ceramic layers.
Another parameter that must be considered is the age of the patient. The color of
young patients shows a whitish tint with an increased brightness, which with age will turn
into an orange color with a decreased brightness. As the patient gets older, the color may
even have a brown tint, with a low degree of brightness.
Increased calcification causes an increase in opacity, and with age the dentin
becomes more opaque, darker in color and more visible through the thinned enamel layer.
Restoration color verification Restoration color verification is significantly improved by the
use of computerized techniques. For example, the Shade Vision system has a feature to
virtually test the color of the restoration, and the SpectroShade system has a way for the
technician to check the restoration electronically before sending it to the office. This check
certifies the correctness and accuracy of the chosen color and reduces the number of
failures, additional sessions needed to redo the restoration.
Being introduced on the market of dental products for a relatively short time, and
with predilection for equipping dental technical laboratories, a series of clinical studies are
still needed, which highlight the superiority of these digital color selection systems and
certify their profitability.
The table below compares the advantages and disadvantages of traditional and
digital color selection systems
Table 6.2. Advantages and disadvantages of traditional and modern color selection
systems
System
Benefits
Disadvantage
Conventional
low cost
subjectivity inconsistency
ease of use
in manufacturing
visual manipulation can be
the choice of color is
transported
affected by the
environment, by the
lighting conditions
Digital
more objectively,
increased costs;
the color can be checked in the interpretation of the
the laboratory,
report depends on the
uninfluenced by the
technician;
environment, the lighting
is not easy to transport
conditions increases
(e.g. Cynovad and Spectro
productivity (reduce
Shade)
working time, fewer
failures)
CHAPTER 8.
ALL-CERAMIC SYSTEMS
Contemporary prosthodontics is overwhelmed by the multitude of ceramic
materials available on the market, making the material selection process difficult for the
clinician.
Achieving successful clinical results involves two important factors: (1)
knowledge and proper selection of the material and (2) the skill of the practitioner which
includes proper handling of the material and proper communication with the dental
laboratory.
WHAT ARE DENTAL CERAMICS?
A ceramic is a product made from a non-metallic inorganic material processed by
firing at high temperature to achieve desired mechanical and optical properties. The
advent of all-ceramic materials has radically changed the therapeutic workflow from
preparation to cementation (da Silva LH, 2017; Bajraktarova-Valjakova E, 2018).
All-ceramic systems are biocompatible, have acceptable long-term clinical
strength and are aesthetically superior. The use of ceramics in dentistry started to
become popular in the sec. The aesthetic characteristics of this material compared to
other materials used are largely responsible for its popularity in the 18th century. Alexis
Duchateu, a pharmacist in Paris integrated dental ceramics, and later in 1903, Charles
Land created the first all-ceramic inlays, onlays and crowns using fired ceramics
(Mörmann WH, 2002).
Technical performance led to the development of new biocompatible ceramic
materials with excellent aesthetics and greatly improved optical properties, but also with
superior mechanical properties and reduced plaque retention (Zarone F, 2011;
Bajraktarova-Valijakova, 2018).
For their everyday use in dentistry, ceramics must meet specific criteria: (1)
hardness similar to dental tissues and prevent crack propagation, (2) adequate
mechanical strength to withstand occlusal forces, (3) superior optical and aesthetic
properties, and (4) predictable in vivo performance that provides long-lasting
restorations.
An ideal ceramic material should be translucent at the incisal margins, opaque in
the cervical area, provide adequate strength and allow preservation of tooth structures.
They can be successfully used for all types of prosthetic restorations(unidental crowns,
inlays ,onlays and veneers (Nikolopoulou F, 2014; Edelhoff, 2011).
Dental ceramics can be classified into two broad categories:
-1. silica-based - feldspathic ceramics, leucite-reinforced ceramics, lithium
disilicate-based ceramics,
-2. oxide-based - zirconium oxide, Y-TZP and aluminium oxide (Allied Market
Research, 2017).
Glass ceramics
The anorganic phase of ceramics is composed of a residual glass phase to
which finely dispersed crystalline phases are added (Gracis S, 2016; Shenoy A, 2010).
The crystalline phase can contain between 0.5% to 99.0% of the composition, but
typically contains 30% to 70% of the final composition (Montazerian M, 2017). The type,
size and volume fraction of the crystalline phase together with the distribution in the
glass matrix are among the important factors in controlling mechanical and aesthetic
properties such as hardness and translucency of the final material. In addition, the
presence of crystalline phase improves the mechanical strength of the final material by
inhibiting crack propagation (Fu L, 2020). The glassy phase also contributes to the
improvement of mechanical properties through marginal grain deposition.
Advantages of glassy ceramic matrix over traditional ceramics include ease
of synthesis process, low shrinkage and improved translucency due to decreased
internal light scattering (Ho GW, 2011; Fu L, 2020). Glazed ceramic matrix is divided
into two subcategories: natural materials such as feldspathic ceramics and synthetic
materials such as lithium disilicate.
Feldspar ceramics
Feldspar ceramics are known as traditional dental ceramics which are
based on a ternary system composed of natural feldspars (potassium/sodium
aluminosilicate), kaolin (Al2O3.SiO2.2H2O), quartz (SiO2), and a few metal oxides as
additives (Saint-Jean SJ, 2014). During the fabrication process, fused feldspar provides
a glassy matrix for the distribution of a disordered silicon tetrahedron lattice.
Feldspar ceramics are silicon-based ceramics available in sintered or milled
form, which have a low to medium flexural strength (65-120 Mpa)(Li R,2014). This class
of materials can be produced in different shades with different degree of opacity and
translucency by adding metal oxide pigments.
In dentistry, opaque feldspathic ceramics are used as a first layer that
protects the underlying metal, followed by a layer of ceramic enamel to reproduce the
natural color of the tooth. Despite their advantageous properties, feldspathic ceramics
are limited to low-stress anterior applications due to lower flexural strength and
increased brittleness.
The perceived color of natural teeth is the result of dentin reflection
modified by absorption, dispersion, and enamel thickness (da Silva LH, 2017).
Translucent porcelain may have a greater effect on the colour of the facets than
opaque substrate. There is a significant correlation between core thickness ratio,
ceramic veneer and restoration colour. Even when there is adequate thickness, clinically
appropriate shades are difficult to achieve because there is a wide range of
translucency between the core materials of all ceramic systems at clinically relevant
thicknesses. Clinicians claim that porcelain with high opacity could be used to reduce
the colour difference of porcelain veneers when cementing on a dark or substantially
discoloured tooth. Various manufacturers have introduced the high opacity porcelain
system and claim superior colour stability on any substrate.
These ceramics are considered to be the most conservative and generally
the most translucent ceramic materials, but they are also the least durable. The high
transparency of the material and its aesthetics create the illusion of natural teeth.
Stratified feldspathic veneers are indicated in the restoration of dyschromic teeth
because the layered porcelain powders offer more flexibility in terms of alternating
between opacity and translucent areas. Because it can be layered in very thin layers
that are applied directly to enamel, this ceramic is considered to be the material that
allows the greatest preservation of remaining tooth structures. If we refer to ceramic
veneers, they require a thickness of 0.2-0.3 mm for each shade changed. Many dentists
choose feldspathic veneers because they can be made thinner than pressed ceramics.
Vitablocs (Vita Zahnfabrik, Bad Säckingen, Germany) are among the most widely used
digitally milled feldspathic ceramics (CAM) with an average flexural strength of 154
MPa. Feldspar ceramic restorations that are bonded directly to the glaze have proven to
be successful in the long term.
Leucit-reinforced ceramics
Leucite-reinforced ceramics are silicon-based ceramics available in sintered,
pressed or milled form. It contains up to 45% leucite by volume, which has a medium
bending strength (120-140 MPa) and compressive strength. Leucite crystals can stop
the propagation of cracks and contribute to an increased strength of the ceramic mass
(Fasbinder DJ, 2002).
Lithium disilicate
Synthetic glass ceramics emerged as an alternative to natural glass
ceramics, with a higher volume fraction of the crystalline phase distributed in the glass
matrix. Currently, lithium disilicate glass ceramics are among the most popular dental
restorative materials (Montazerian M, 2017).
Lithium disilicate is a silicon-based ceramic available in sintered, pressed or
milled form (Zarone F, 2016). Lithium disilicate glass ceramics are based on the SiO2Li2O system composed of randomly oriented lithium disilicate crystals, resembling fine
platelets, or rods at concentrations higher than 70% and a lower concentration of lithium
orthophosphate (Li3PO4) crystals dispersed heterogeneously in the glass matrix (SaintJean SJ, 2014; Ho GW, 2011). The higher concentration of crystalline phase and tighter
interconnection of the synthetic glass ceramic matrix exhibit significantly higher strength
of about 350 MPa and fracture toughness of 2.5 MPa m1/2 compared to natural
feldspathic porcelain (Ho GW, 2011; Ritzberger, 2010). Secondary to the improved
mechanical properties, this restorative material can have a wide range of applications,
including resin-cemented veneers, crowns, and 3-unit bridges up to the second
premolar. IPS e.max (Ivoclar Vivadent, Schaan, Liechtenstein), a lithium disilicate
ceramic, was developed in part by Prof. Wolfram Holland at Ivoclar Vivadent. After the
development of clinical applications, the material was released to the dental community
about 12 years ago. This ceramic material is much researched, and many authors have
described its physical properties. The effects of lithium disilicate on fracture potential
and tensile strength have been tested, as well as the effects of physiological ageing in
aqueous media, abrasivity, wear, and surface roughness. The results of the studies
revealed that almost all clinical requirements considered ideal for dental ceramics used
in clinical practice have been met or exceeded.
Celtra Duo (Densply Sirona,York, PA) is one of the newest lithium silicatebased ceramics available on the market. It is a zirconia-reinforced lithium silicate,
containing around 10% zirconium oxide. The manufacturer claims that the smaller
crystal size and ultrafine microstructure material lead to increased mechanical strength.
Celtra Duo lithium silicate-based ceramics are available in pressable or milled form and
can be used for crowns, partially cemented crowns (inlays, onlays, veneers) (Lawson
NC, 2016).
Another lithium disilicate-based ceramic material is GC Initial LiSi Press (GC
America, Alsio, IL) which have high strength and density. This new lithium disilicate
ceramic provides an even distribution of microcrystals, leading to excellent mechanical
and optical properties. Recommended indications for pressed ceramics are crowns,
inlays, onlays, veneers, and 3-unit fixed partial dentures up to the second premolar
(Hallmann L, 2019).
Monolithic full-contour restorations adhesively fixed with resin cement are
fabricated from lithium disilicate even for higher stress situations at the molar level.
Lithium disilicate attests to the safety of its use for any kind of single restorations or
small fixed partial dental prostheses in the frontal area. Due to the glassy properties of
this material, adhesive cementation is recommended. However, bonding to dentin gives
less predictable results for these restorations because of the flexibility of dentin. Enamel
bonded restorations are much more predictable, as enamel is known to have a
significantly higher rigidity than dentin.
Aluminium oxide (alumina)
Alumina (Al2O3) is a naturally occurring oxide with a wide range of industrial
applications, such as abrasive materials secondary to its high hardness. In addition to
high hardness, superior wear and corrosion resistance along with biocompatibility have
made this material a popular candidate in dental medicine (Ben-Nissan B, 2008). The
very fine grain size of medical-grade alumina ceramics prevents static fatigue and
deflects cracks while under load. All these properties have made alumina a desirable
substrate for a wide range of medical applications, including dental restorations and
orthopaedic applications. However, alumina ceramics are prone to mass fracture due to
their high elasticity (Scherrer SS, 2008). Nobel Biocare's Procera AllCeram (Zürich,
Switzerland) (the first dense polycrystalline ceramic) and In-Ceram AL, a product of
VITA Zahnfabrik, are the best known representatives of this type of ceramic.
Zirconium oxide (Zirconia)
Zirconium oxide ceramics use CAD-CAM techniques to fabricate a wide
range of prosthetic restorations, crowns, bridges, implant abutments, mobile and
removable dentures. Y-TZP zirconium oxide is milled in the presintered phase, then
sintered to reduce its volume by about 20% (Shenoy A, 2010).
Zirconia (zirconium dioxide) is a polycrystalline ceramic with excellent
hardness, strength and fatigue resistance. Depending on the temperature, this
polymorphic ceramic can be formed of 3 different crystallographic phases, such as the
cubic phase formed at temperatures above 2300°C, the tetragonal phase at
temperatures between 1100°C and 2300°C, and the monocyclic phase occurring at
room temperature up to 1100°C (Bona AD, 2015; Manziuc M-M, 2019).
By adding stabilizing oxides, such as magnesium, yttrium, cerium is
developing the characteristic of transformation toughning - the so-called martensitic
transformation. Partially stabilised in the tetragonal phase under the action of
mechanical stimuli, it transforms into the monocyclic phase, which is much more stable
and achieves a volume increase of 4%. This growth stops cracks propagating in the
material through compression, giving zirconium oxide its reputation as a smart material.
The stable crystalline phase for zirconia at room temperature and atmospheric pressure
is monocyclic. The monocyclic phase transitions into the tetragonal phase at around
1170 °C with a shrinkage of about 5% and a slight expansion during cooling. With
increasing temperature up to 2370 °C, zirconia passes from tetragonal to cubic phase
with a subsequent change in volume of 2.3% (Bona AD, 2015).
Zirconia has similar elasticity to stainless steel but superior biocompatibility.
In addition, low plaque retention results in the maintenance of good periodontal health
after the application of restorations made of this material (Gautam C, 2016). There are
probably over 50 different zirconia-based ceramics and often the technician or clinician
has no idea what the manufacturing standards were for a particular zirconia block or
disc used to fabricate restorations from different sources. The fatigue strength depends
on the manufacturing standard applied by the manufacturer. Yttria-stabilised zirconia
(flexural strength >900 MPa) is indicated for clinical situations including anterior and
posterior crowns, inlays, implant bridges/crowns, 3-unit fixed dentures, fixed arch
restorations (up to 14 units)(DC-Zircon).
Zirconium dioxide can also be used
when a large amount of dental tissue is missing or when there is a risk of bending and
stress, for posterior unidentate restorations and for posterior multi-unit fixed
restorations, or when adhesive cementation is problematic due to subgingival margins.
The flexural strength of widely used zirconia-based dental ceramics ranges from 1.0 to
1.4 GPa (Glidewell [Newport Beach, CA] BruxZir Solid Zirconia, 1-1.4 GPa; Ivoclar
Vivadent Zenostar T, 1.2 GPa; Katana Zirconia [Kuraray Noritake Dental Inc., Okayama,
Japan]).
Due to their high opacity, several studies have attempted to increase the
translucency of zirconia materials by modifying their microstructure, including
decreasing their aluminium content, increasing their density, decreasing their grain size,
adding zirconia in the cubic phase, and decreasing the amount of impurities and
structural defects (Bajraktarova-Valjakova E, 2017). Crystalline grain size is the
microstructural feature that is closely related to the translucency adjustment of
polycrystalline ceramics. The creation of ceramic materials with high translucency has
been achieved in the past by increasing grain size during sintering. Larger grains lead to
a smaller number of neighbouring grains, thus reducing light scattering. For Y-TZP,
larger grains have been shown to be detrimental to both mechanical properties and
tetragonal phase stability. Therefore, zirconia translucency cannot be achieved by
increasing the grain size. Low translucency has made ceramic materials from zirconia to
be a little more aesthetic and it was a challenge for the technician to achieve aesthetic
results.
An alternative method of fabricating Y-TZP with high translucency is
achieved by significantly decreasing the grain size. However, the grain size should be
decreased until a critical value is reached which results in the attenuation of the socalled birefringence phenomenon . Birefringence occurs in Y-TZP due to the large
amount of tetragonal crystalline phase (>90%), which is a crystal that has different
refractive indices depending on the crystallographic orientation in the microstructure.
Such anisotropic behaviour related to refractive index variation causes light scattering.
Another way to overcome the effects of light scattering, is the use of cubic
zirconia, which provides optical isotropic behaviour, increasing translucency
(Bajraktarova-Valjakova E, 2017). However, the increase in translucency (due to the
increase in the content of the cubic structure) leads to a decrease in bending strength.
The flexural strength of translucent(super and ultratranslucent) zirconia ranges from 500
to 800 MPa (Glidewell BrixZir Anterior and Ivoclar Weiland Zenostar MT, and Katana
[Noritake] STML, 750 MPa and UTML 560 MPa). It has been reported that zirconia
translucency is variably dependent on processing method, manufacturer formulation,
and laboratory sintering times and temperatures.
Updated classification of ceramic materials(Mc Laren)
Another more updated classification of all-ceramic materials was developed
by Edward Mc Laren in 2015. According to this classification there are 4 main classes of
ceramic materials:
CLASS I (Powder/Liquid or Feldspar Ceramic)
Powder and liquid ceramics are created from materials containing silicon
dioxide, a glass matrix and varying amounts of crystalline phase within that glass matrix
(example: Creation Porcelain, Jensen Dental, www.jensendental.com; Ceramco3,
DENTSPLYInternational, www.dentsply.com; EX-3, Kuraray Noritake Dental, Inc.,
www.kuraraynoritake.com).
Class I ceramics include feldspathic ceramics. Feldspathic materials
currently available include : Vita VM 13, Vita Zahnfabrik, www.vita-zahnfabrik.com;
Vintage Halo, Shofu, www.shofu.com.
Class I ceramic materials are handmade. They are the most conservative
and generally the most translucent ceramic materials, but they are also the least
durable. Powder and liquid ceramics are ideal for cases where we have significant
amounts of glaze remaining.
Because it can be layered in very thin layers that are applied directly to the
enamel, this ceramic is the material that allows the greatest preservation of remaining
tooth structure. If we refer to ceramic veneers, Class I ceramics require a thickness of
0.2 mm to 0.3 mm for each shade changed. This class of material is most suitable for
anterior restorations, but can occasionally be used for premolars and rarely for molars,
providing all parameters at a very low risk level.
CLASS -II (Glass ceramics)
The composition of Class II ceramics is similar to that of Class I, as both
ceramics possess a glassy matrix, but the two classes differ in their crystal phase ratios
and crystal types. In Class II ceramics, crystal types can be added to the glass or grown
in the glassy matrix.
- CLASS-II a
Materials in this subdivision have a low-moderate leucite content (less than
50%). Such materials (e.g. IPS Empress® CAD, Ivoclar Vivadent,
www.ivoclarvivadent.com; Authentic®, Jenson Dental; VITABLOCS® Mark II, VITA
Zahnfabrik) contain less than 50% crystals and behave more like glass, requiring
bonding.
Like all Class II materials, which have come to be known as glass ceramics,
CL-IIa materials have the same clinical indications as Class I, i.e. anterior teeth,
premolars and in rare situations molars. In addition, their clinical success in situations of
increased occlusal stress or when we have more exposed dentin has been documented
over time. They are very translucent, but require slightly larger sizes for processing and
aesthetics/shade matching (e.g. a minimum thickness of 0.8 mm to layer this ceramic).
Materials in this sub-category have demonstrated increased strength. These dense
materials containing glass and leucite are suitable for thicker veneers, crowns in the
front, inlays and posterior onlays, but only when long-term adhesion can be ensured.
CLASS-II b
This is a new sub-category that has a moderate to high content (more than
50%) of crystals containing glass or glassy ceramics. It presents itself as a
homogeneous glass, which after secondary treatment creates and grows crystals. This
process provides improved physical and mechanical properties by increasing the
number of crystals and generating compressive stress around the crystals. An example
of a material in this subcategory is lithium disilicate (e.g. IPS e.max®, Ivoclar Vivadent).
CLASS III (High strength crystalline ceramics)
Class III materials are high strength crystalline ceramics that have little or no
crystalline phase and are also produced by industrial processes.
- CLASS III a
CL-IIIa materials are manufactured by creating a porous matrix that is
formed into a block and then processed into its final form using CAD/CAM technology,
after which a second phase follows when a material melts and fills the pores of the first
material. This material is disappearing from the market, being replaced entirely by 100%
polycrystalline ceramics.
- CLASS III b
High strength, 100% crystalline ceramic CL-IIIb was originally represented
by alumina-based materials (e.g. Procera®, Nobel Biocare, www.nobelbiocare.com).
More recently, zirconium oxide based ones have been introduced (eg LAVA™, 3M
ESPE, www.3MESPE.com; Prettau®, Zirkonzahn, www.zirkonzahn.com). Alumina
systems have proven successful for single tooth restorations but have gradually been
replaced by zirconia and lithium disilicate.
Whether alumina or zirconia, both materials have demonstrated greater
strength than CL-I and CL-II materials and can be used in the fabrication of a framework
to replace the metal framework.
These materials can be veneered with ceramic layers, resulting in superior
strength and significantly improved aesthetics.
Materials in Class III typically require a thickness of 1.2 mm to 1.5 mm,
depending on the color of the substrate.
Currently, more translucent versions are being used for monolithic
restorations in zirconia. The first material commercially available in this category
was BruxZir® by Glidewell Laboratories. Zirconia used in dental laboratories is
typically supplied in the form of presintered discs.
There is currently a wide range of zirconium oxide-based materials used
for prosthetic restorations. This class of materials has evolved significantly in
recent years, with the emergence of translucent, super, and ultra-translucent
materials designed for esthetic monolithic restorations.
Manufacturers recommend adhering to minimum dimensions for
connectors when fabricating fixed prostheses to avoid failures. The maximum
mesiodistal distance between abutment teeth for zirconia should ideally not
exceed 25 mm. As indicated by fractographic studies (Rekow, 2011), most
fractures in all-ceramic fixed prostheses occur due to stress concentration at the
connector area. Zirconia-based materials, especially the newer ones with
increased translucency, allow the creation of monolithic fixed prostheses that can
have sufficient thickness, eliminating the need for veneering with ceramic.
In the last five years, zirconium oxide-based ceramics have emerged that
are super-translucent or ultra-translucent but have lower strength, approximately
600 MPa, which affects the range of indications and cementation procedures.
Class IV (Metal-Ceramic)
Materials in class IV are essentially materials from class I fused with a
metal substrate, allowing their use in clinical situations with increased stress
where conventional crowns are necessary. Like class III materials, class IV
materials, namely metal-ceramics, demonstrate higher strength, but their
aesthetic characteristics are limited. Metal-ceramic materials require a thickness
of at least 1 mm to achieve a natural-looking esthetic. Metal-ceramics exhibit
similar qualities to class III materials based on zirconia, but they are not as
sensitive to ceramic firing, unlike zirconia.
The materials in CL-I can be aesthetically enhanced by using
a metal framework with a higher gold content (e.g., Captek™, Argen
USA Inc., www.captek.com).
The chemical composition and characteristics of today's dental ceramic
materials provide a framework for determining the class of ceramics that can be
used for a specific clinical case. However, there are other factors that influence
material selection, including the preservation of tooth structure, the possibility of
adhesive cementation, aesthetic requirements, smile design, and tooth shade.
Class I and Class II materials offer improved aesthetics but have lower strength.
It's important to note that all types of ceramics are less resistant to shear
and fracture forces compared to compressive forces. However, by controlling the
stress to which these materials are subjected, they can be successfully used in
fixed prosthetic restorations.
The use of integral ceramic systems for fixed prosthetic work has its
limitations and specific requirements. Correct diagnosis and patient selection are
critical factors for success. Other factors that may restrict the use of integral
ceramic systems include limited interocclusal space, deep occlusion, severe
bruxism, and parafunctional activity. The selection of integral ceramic systems
depends on specific indications for each clinical case, and the clinician must pay
attention to preparation details, adaptations, and the cementation protocol,
considering the potential risks associated with each individual case.
MATERIAL SELECTION FOR CERAMIC RESTORATIONS
To choose the appropriate dental material, important parameters should be
considered:
1.
Position: The clinician should consider whether the restoration will
be used for the anterior or posterior region. For anterior restorations, a more
translucent ceramic material with lower mechanical strength leads to
favourable aesthetic results. However, for posterior restorations where
translucency is not important, a stronger ceramic material such as alumina,
zirconia, or lithium disilicate is recommended.
2.
Design: The clinician should consider the design of the ceramic
restoration, whether it's a single unit or a multi-unit FDP (fixed dental
prosthesis). Certainly, for multi-unit restorations, a stronger ceramic material is
recommended.
3.
Strength: It's necessary to assess the biomechanical risk and
analyse occlusal forces. For medium to low biomechanical stresses, feldspathic
ceramic or lithium disilicate is recommended. However, for medium to high
occlusal demands, stronger ceramics such as alumina or zirconia are more
suitable.
4.
Substrate: The tooth or material substrate is one of the most
important criteria for selecting ceramic restoration materials. There are three
factors to consider: the percentage of remaining enamel, the percentage of
remaining dentin, and the presence or absence of discoloration.
In the anterior sextant, when there is more than 50% remaining enamel
substrate, the use of feldspathic ceramic is favoured due to its increased
translucency and optical properties. However, when the amount of remaining
enamel is less than 50% in the presence of discoloration, lithium disilicate is the
material that should be chosen.
In the posterior sextants, feldspathic ceramic is contraindicated due to its low
mechanical properties. For ceramic restorations made from lithium disilicate, the clinician
should always consider adhesive bonding to the underlying tooth structure. For
restorations made of alumina or zirconia, adhesive cementation is necessary only if
retention is compromised (height <3mm and a convergence angle >20°).
5.
Translucency: To achieve successful aesthetic results, it is
important to consider the translucency versus opacity of the ceramic restoration
material. Generally, in the aesthetic zone, a material with high translucency is
desired, while for the posterior region, high opacity is favorable.
FACTORS INFLUENCING THE CHOICE OF CERAMIC
MATERIAL AND RESTORATION TYPE
Mechano-chemical properties, biological factors, as well as
aesthetic requirements are the foundation for selecting an "allceramic" material from which a fixed prosthetic restoration will be
made.
From the range of aesthetic materials available in the dental
products market, the decision for a specific material should be based
on the individual clinical situation, analysing the advantages and
disadvantages of each material to choose the optimal one.
Restorations in the frontal zone pose an aesthetic risk when
modifying the smile design is desired. This risk involves either
altering the proportions and ratios of the teeth, making minor
positional and alignment changes, or modifying the color in the
context of the facial features and the lines that characterize it. When
it is necessary to mask the discoloration of an abutment or when a
higher degree of translucency is required to achieve the most natural
tooth appearance, the choice of the appropriate material should be
based on the optical properties of each material.
To prevent occlusal risks, restorations should be carried out
after a proper occlusal analysis of the models mounted in the
articulator, in order to anticipate signs or symptoms of TMJ pathology
or occlusal disorders of muscular origin. If dealing with a patient at
high occlusal risk, special attention is required when selecting the
ceramic material for the restoration, especially for patients with
bruxism.
When restoring the entire arch, extra attention to detail is
necessary to ensure occlusal harmony that provides a healthy
stomatognathic system while minimizing stress on the restoration.
When opting for all-ceramic adhesive cemented restorations,
the amount of remaining enamel is essential for the success of the
restoration. The minimally invasive and conservative principle is a
crucial requirement in tooth preparation for all-ceramic restorations.
The quality and quantity of dentin at the cementation interface can
compromise the longevity of the restoration, especially if it is sclerotic
or carious. If there is increased sensitivity to cold, it indicates that the
collagen network in the dentin has been significantly altered, which
will also compromise the adhesion of the final restoration.
Additionally, if proper isolation cannot be achieved during an
adhesive cementation procedure, failure is imminent. In the case of
subgingival preparations, patients with limited mouth opening, or any
other situation where proper isolation is impossible, choosing an allceramic system that can be conventionally cemented (CIS, CIMR) is
preferred.
Strength of Ceramic Materials
Based on compressive and fracture strength, ceramic
materials can be ranked in the following decreasing order: zirconium
oxide-based ceramics (800-1200 MPa), alumina-infiltrated ceramics
(236-600 MPa), lithium disilicate ceramics (300-500 MPa), leucite
ceramics, and feldspathic ceramics (between 100-120 MPa) (Lawson
NC, 2016).
Translucency of Ceramic Materials
Ceramics with moderate translucency and opacity are
indicated for discolorations, metal-ceramic crowns, and implant
abutments. Although these materials can mask discolorations, there
are situations where a more opaque material is necessary. Among
these moderately translucent materials, nano-ceramic resin materials
(Lava Ultimate [3M ESPE]) and lithium disilicate (e.max Ivoclar
Vivadent, LT, or MT) can be mentioned.
Ceramic materials with minimal translucency and high opacity
(capable of covering discolorations) include CAD/CAM blocks made
of zirconium oxide and yttrium-stabilized zirconium oxide, aluminium
oxide and zirconium oxide coping, CAD/CAM blocks made of lithium
disilicate (e.max HT), and monolithic zirconium oxide.
Fully opaque materials include:
•
Monolithic zirconium oxide
•
Pressed-to-metal (PTM) systems (Authentic, Jensen
Industries)
•
Ceramic veneering for metal frameworks made of noble
alloys, semi-noble alloys, titanium (Titanium, Platinumpalladium/high gold hybrid: Captek).
Based on these classifications, we can make an informed
choice of the appropriate material depending on the prosthetic
restoration we are planning to create.
The probability of survival for all-ceramic prostheses increases
with the increase in the modulus of elasticity. Periodically, ceramic
surfaces need to be polished (using polishing stones and rubber
wheels designed for ceramics) to reduce the potential for wear by the
enamel surfaces of opposing teeth.
The thickness of connectors should be adjusted depending on
the material from which they are constructed. For lithium disilicate,
the occlusal-gingival thickness should be around 4-5mm, and the
buccal-lingual thickness should be 3-4mm. For YTPZ polycrystalline
D, the dimensions are OG (occlusal-gingival) = 2.8mm and D (V-L)
(buccal-lingual) = 2.7mm. Especially in the anterior zone, where
aesthetic requirements are the most demanding, knowledge of each
material's characteristics allows us to thin the connector to the
maximum extent possible, helping us achieve the final aesthetic
result without compromising the structural strength and creating
adequate space for interdental papillae, which should be between 45mm in the cervico-incisal direction from the free gingival margin.
Longevity and Prognosis of All-Ceramic Restorations
It is widely accepted that fracture is the most common cause
of failures in all-ceramic restorations, regardless of the fabrication
method. More translucent ceramics are more brittle than the opaquer
ones (Denry I, 2014), which means that the ideal ceramic material for
all applications has not yet become a reality. Regarding the marginal
adaptation of all-ceramic restorations, it is influenced by several
sources of error related to scanning, design, limitations of the milling
process, and the fractures that may occur during milling. Nakamura
(2003) and Santos (2013) have highlighted marginal discrepancies
ranging from 53-67 microns, and these discrepancies tend to
increase with more angled preparations (Nakamura M, 1978; Santos,
2013). CAD/CAM materials with the most studies to date are the
ones that appeared first, namely ceramic blocks.
The 10-year survival rate of leucite ceramics has exceeded
90%, according to studies by Della Bona and Kelly (Della Bona,
2008). In addition, ceramics with a high glass content are sensitive to
stress corrosion due to the wet oral environment, which can initiate
and propagate cracks (Shenoy, 2010).
The current formula of lithium disilicate in the CAD/CAM
version has been available only since the late 2000s. There are
already several studies, and their number is increasing over the
years (Fasbinder, 2010).
Monolithic restorations made of cubic zirconia have proven to
have better light transmission than layered ones. Depending on the
differences between them in terms of crystalline phase, processing
method, the loads they are subjected to, clinical studies have shown
survival rates of over 90% (Strub, 2013).
Wear/fracture of ceramic restorations can occur during milling,
other laboratory stages, cementation, or during function. Defects that
can occur in ceramic masses during the milling process can act as
stress concentration factors that can initiate a crack in the material,
leading to subsequent fracture. Another cause of defects can be
attributed to laboratory handling, particularly sandblasting treatment
to prepare the restoration before veneering with ceramic. The
damage resulting from this process may not be immediately visible
but can compromise fatigue resistance in zirconia and alumina
restorations (Denry I, 2013).
The survival rate for CAD/CAM fixed zirconia prostheses varies around 70-80%
(Raidgorski, 2012), with the major causes of failure being material chipping,
delamination, intermediate framework fracture, and issues related to the abutment
teeth.
Clinical experience highlights that there are many factors that can affect the
occlusion of crowns made through conventional techniques. Errors in achieving optimal
occlusion can also occur with CAD/CAM techniques, as the design and milling steps
can introduce occlusal errors. Differences in occlusal contacts can exist between the
proposed design and the milled crown. Some materials, like leucite-based and disilicate
ceramics, pose fewer problems for intraoral occlusal adjustments compared to strong
materials like zirconia, which can create significant challenges for clinicians during
occlusal adjustment and subsequent polishing.
Normal occlusal forces range between 9 and 180N, with a duration of 0.2-0.33
seconds during chewing (Larson, 2009). The maximum bite force in young individuals
falls between 516-532 N in the posterior region. Occlusal forces are greater towards the
back, with the second molar bearing over 55% of the maximum bite force, while incisors
handle about 20%. When these forces are directed onto a single tooth covered with a
restoration, the resulting stress can be amplified.
MOD cavities can weaken the remaining dental structure. For crown restorations,
inclined planes and cusp inclinations receive higher forces, and maintaining occlusal
contact points, not contact zones, is recommended to minimize apical stress. In the
case of crowns, widening the contact area acts like a "snowshoe" that distributes
chewing forces over a larger surface, reducing stress within the crown and the risk of
fracture. Caution is advised when opting for all-ceramic restorations in high-stress molar
areas.
When multiple fixed prosthetic restorations are indicated, zirconia is the material of
choice, but careful consideration is needed when deciding the size and shape of the
connector, particularly regarding the gingival aspect (rounded, concave).
Abrasive adjustments should be avoided after the fixed prosthesis has been
milled and sintered. Concerning wear on opposing teeth, well-polished zirconia is less
abrasive than glazed and pigmented zirconia or conventional ceramics.
In terms of aesthetic limitations of CAD/CAM crowns, there are several aspects
to consider to minimize aesthetic risk. After removal from the milling machine,
restorations made from feldspathic and leucite ceramics can be finely polished and then
cemented, especially in posterior and intracoronal restorations.
For the anterior region, aesthetic limitations require staining/pigmentation before
glazing. However, this is often insufficient to meet the aesthetic preferences of patients,
especially those with complex intrinsic coloration of adjacent teeth to the future
prosthetic restoration. In this situation, instead of full-contour milling, a coping is
produced, allowing the technician to apply successive layers of ceramics with different
colors to mimic the appearance of natural teeth.
The choice of the most suitable ceramic material depends on the individual
clinical case, which imposes specific aesthetic and strength requirements. More
translucent materials are more aesthetic but less resistant, while opaque materials like
zirconia offer strength suitable for a wide range of prosthetic restorations.
FIXED PROSTHETIC RESTORATIONS WITH IN-OFFICE CAD/CAM SYSTEMS
Materials for in-office CAD/CAM prosthetic restorations
"The widespread use of CAD/CAM restorations in the dental office has expanded
the variety of restorative materials. For practitioners, choosing the appropriate material
is challenging due to the wide array of materials available in the market.
The first in-office CAD/CAM inlay was produced in 1985 from a ceramic block
containing fine filler feldspathic ceramic (Vita Mark 1, Vita Zahufabrik).
Feldspathic ceramic was initially used for small occlusal inlays, but the desire to
extend the indications for CAD/CAM restorations (onlays, crowns) led practitioners to
work with mechanically stronger materials. This led to the development of leucitereinforced ceramics.
To allow for rapid milling, some materials are marketed in a pre-crystallized form.
Crystallization is necessary after milling to achieve the desired shade and final
mechanical strength.
In recent years, softer but less brittle materials have emerged, namely resin
composite materials. They are much less mechanically robust but have the property of
deforming before fracturing, unlike ceramic materials.
The next step was to enhance the mechanical bonds of these resins by
incorporating ceramic particles. Currently, manufacturers are attempting to combine the
advantages of these two material families, offering a ceramic network infiltrated with
resin polymers.
Presently, manufacturers offer over 20 types of CAD/CAM blocks for in-office
use. These are available in different sizes, shades, and translucencies and may require
post-milling treatment, which varies depending on the material type.
The blocks of materials used for CAD/CAM restorations are homogeneous,
dense, and free from imperfections. These materials are available in various chromatic
ranges and translucencies, allowing for improved aesthetics in restorations. Surface
characterization and pigmentation, followed by firing, can be performed for aesthetic
perfection. Ten years ago, there were only about 5 materials available for computerized
milling, but today there are over 50 diverse materials to choose from based on each
clinical case. This includes a wide range of materials, from ceramics to composites,
hybrid materials, and metals (Van Noort, 2012; Fasbinder, 2010).
It is known that restorations created with in-office CAD/CAM systems are
monolithic, meaning the entire restoration is composed of a single material, unlike
bilayer restorations that consist of a core (substrate) onto which a veneer layer is
applied.
Monolithic restorations have some unique characteristics. Being industrially
produced, they have a dense, homogeneous structure without porosities, maximizing
the physical properties of the material. They are delivered in the form of blocks specific
to each milling machine. Milling machines use a subtractive (wet milling) system to
shape the desired contour of the restoration created by digital design. After milling,
depending on the characteristics of each material, a specific time and technique are
allocated to complete the restoration. These materials are suitable for either hard milling
(hard state) or soft milling (soft state). Hard milling refers to the milled block being in its
final microstructural form. After milling, it only needs polishing or glazing before
cementation. Soft milling refers to blocks that are milled in the so-called green form,
which subsequently needs to undergo heat processes to reach the final microstructural
form. Hard milling refers to composites, hybrid composite/ceramic materials, and certain
ceramics, which are typically used for single-unit restorations (Miyazaky, 2009; Levine,
2009)."
Classification of CAD/CAM Dental Materials for In-Office Use
CAD/CAM dental materials for in-office use can be classified from a clinical
perspective into four generations.
1. First Generation - Feldspathic Ceramics
Materials of the first generation belong to the category of feldspathic ceramics
(e.g., Vita Mark II, Vita) and leucite-reinforced glass ceramics with low to medium leucite
content (e.g., Empress CAD, Ivoclar). They were introduced for commercial use before
the 1990s and occupied over 90% of the market until the 2000s. They were also the
most studied materials in terms of longevity. When indications and operator times are
strictly adhered to, the success rate is sufficiently high. Some of the first CAD/CAM
blocks were Vita Mark II (Vita, Germany), introduced in 1991. Feldspathic ceramics
used for veneering metal frameworks are pressed at high pressure and temperature. It
is currently one of the most widely used ceramic blocks with a broad range of
indications, such as crowns, especially in the anterior region, inlays/onlays, and
facades. Being a less resistant ceramic, if sufficient thickness is not ensured, fractures
can occur. After adhesive cementation, the strength can increase to 350 MPa.
Aesthetic characteristics are good, with the material exhibiting exceptional
translucency but no fluorescence. Recently introduced Trilux blocks have three color
gradation levels, while TriluxForte has four color gradation levels, and RealLife blocks
(Vita) have two levels of translucency, dentin and enamel.
As Vita Mark II blocks do not exhibit fluorescence, after polishing and
cementation, the restoration will have a darker shade. This should be considered when
selecting the acrylic cement. It is important to use an appropriate cementation protocol
and not sandblast the restoration's inner surface, as microcracks may occur.
Feldspathic ceramic blocks introduced more recently by Dentsply/Sirona CEREC Blocks
have their own color key to facilitate block color selection.
IPS Empress CAD (Ivoclar), a leucite ceramic, contains approximately 35-45%
leucite load, similar to IPS Empress 1, but with smaller particle sizes between 1 and 5
microns. The presence of the glassy component in these materials allows them to be
etched with hydrofluoric acid, treated with silane coupling agent, and then adhesively
cemented (bonded) to the prepared tooth with resin cements. Shear bond strength is
approximately 160 MPa, which increases through the adhesive cementation process.
Currently, they are available in three translucency variants (HT, LT, and Multi), with the
latter being the most aesthetic. Suitable blocks with different gripping chucks are
available for each type of milling machine.
2. Second Generation - Reinforced Ceramics with Increased Leucite
Content (E.g., e.max CAD)
The second generation is represented by fortified ceramics with increased leucite
content based on lithium disilicate, with e.max CAD by Ivoclar being the most
representative. It consists of approximately 40% 0.2-1 micron-sized lithium disilicate
crystals, offering much better flexural and fracture strength compared to feldspathic
ceramic materials (which have low glassy content). They are sold in a partially
crystallized (soft) state, allowing for easier milling, followed by a crystallization
completion process through firing in a ceramic oven at around 850°C for 25 minutes.
In its uncrystallized state, the blocks are ivory-colored and achieve the desired
color after crystallization, with a contraction of approximately 0.2%. The final result is a
ceramic glass with granules of about 1.5 microns and 70% volume within a glassy
matrix. E.max CAD exhibits characteristics similar to Vita blocks but also has
fluorescence, extending its indications to anterior restorations. They are available in
over twenty different chromatic shades and three different translucencies (low, high, and
medium), providing versatility in their applications.
Another category of materials that emerged after 2013 is zirconia lithium silicate
(ZLS) or zirconia-reinforced lithium silicate. It consists of spherical particles with
dimensions of 400-500 nm infiltrated into a lithium silicate matrix. Vita Suprinity (Vita)
and CeltraDuo (Dentsply) are part of this category, developed through the collaboration
of Dentsply Degudent and Vita but marketed separately. Two types of blocks are
available, tooth-colored and transparent. The transparent ones undergo a crystallization
process at 840°C and transform into the desired tooth color. This material exhibits
increased translucency but lower strength (200 MPa). If subjected to post-thermal
treatment, the strength increases to 370 MPa, according to studies by Larson in 2013.
3. Third Generation - Hybrid Materials
Recently, so-called nanoceramic resins and hybrid ceramic materials have been
introduced. They combine the ease of manipulation similar to composites with the
strength and final lustre of ceramics. These materials can be easily milled and have less
abrasive effects on opposing teeth. Lava Ultimate (3MESPE) contains silicon particles
of 20 nm, zirconia particles of 4-11 nm, which is approximately 80% ceramic load. It is
the third generation of ceramic materials launched in the USA in 2011. This hybrid
material offers improved strength (250 MPa), increased elasticity, and is less brittle.
Currently, there are nine different colors and two different translucencies (LT and HT)
available for this material. After milling, restorations are polished using suitable rubbers,
brushes, and pastes and can be cemented. Initially, indications were extensive, but they
have now been restricted to single-unit inlay/onlay restorations. The company 3M ESPE
has withdrawn the indication for crowns. Lava Ultimate (3MESPE) Cerasmart by GC
belongs to the same category of nanoceramic materials, with the advantage of
fluorescence closer to dental structures and is considered to absorb forces due to its
structural flexibility (force-absorbing nano-ceramic resin) (Sorrentino, 2018).
Vita Enamic (Vita, Germany) is also part of the hybrid ceramic group and consists
of a double network structure in which ceramic and polymer are interconnected.
According to the manufacturer, the material combines the advantages of composites
and ceramics in a single product, offering strength and elasticity, thus preventing
fractures. On the other hand, the polymer network reduces the risk of being brittle. The
flexural strength is 170 MPa, relatively low. Milling time is greatly reduced
(approximately 30%), but the adhesive cementation protocol ensures an increase in
strength. Approximately 100 restorations can be produced with a single bur. This
Cerasmart GC material is suitable for detailed milling (inlay/onlay). Vita Enamic has
multiple advantages, including stopping the propagation of fissures, a feature present in
zirconia oxide. However, there are some controversies regarding the use of these
materials in posterior areas with high stress concentration.
4. Fourth Generation - Monolithic Zirconia (FCZ)**
The fourth generation of in-office CAD/CAM materials refers to full contour
zirconia (FCZ) or monolithic zirconia. Zirconium oxide (zirconia) was introduced
in dentistry over 15 years ago, but over time, it has continuously improved in
terms of clinical and aesthetic performance. Zirconia-based ceramics have
become among the most popular types of all-ceramic restorations today. They
use CAD/CAM technology to manufacture a wide range of prosthetic
restorations, including crowns, bridges, implant abutments, removable and
retrievable prostheses, etc. Zirconium oxide (YTZP) is milled in a pre-sintered
state, followed by a volume reduction of approximately 20% during sintering.
Since 2013, pre-sintered zirconia blocks have been marketed for soft milling in
the dental office.
Zirconia ceramics can be manufactured by two methods:
- Milling an enlarged refractory model, isostatic pressing of zirconia powder,
sintering, and then veneering with ceramic (Procera Zirconia).
- Milling a digitally enlarged restoration from a partially sintered block to
compensate for sintering shrinkage. This compensation can be achieved through
digital data manipulation, ensuring uniform and controlled volumetric shrinkage.
After soft milling of colored blocks, they undergo sintering at a temperature below
1500°C (approximately 7 hours), followed by the final polishing process. During
sintering, zirconia contracts and becomes denser. As the material does not have
a glassy phase, it is rather opaque. By varying the composition or the sintering
process temperature, zirconia's translucency can be manipulated. Currently,
there are zirconium oxide-based materials that exhibit increasing levels of
translucency, allowing for the creation of aesthetic monolithic restorations,
especially in the anterior region. The current trend is to produce monolithic
restorations as one of the most common sources of failure is the
fracture/cracking of the veneering material. Additionally, the entire manufacturing
process is simplified by creating monolithic restorations.
A recently introduced material is e.max ZirCAD Prime, which combines 3YTPZ
and 5YTPZ in its composition, providing incisal translucency (from 5YTPZ) and
structural strength in the cervical half (from 3YTPZ).
Zirconia-based ceramics can be manufactured through milling a block of dense
sintered material in a soft, partially sintered, or green state. Hard (tough) milling
of zirconia ceramics requires more robust milling machines, typically found in
dental laboratories. Supporters of hard milling believe that the edges are much
more accurate, but critics argue that this milling process can induce microcracks
in the material. Tool wear is much faster, explaining the decline of this type of
milling in favour of soft milling. Possibly in the future, with the introduction of
ultrasonic milling technologies (specifically diamond instruments accelerated by
ultrasonic piezoelectric vibration), hard milling may regain popularity.
The clinical stages of making prosthetic restorations with in-office
CAD/CAM systems are as follows:
The concept of same-day dentistry (restorations in a single session) is possible
with the help of in-office CAD/CAM systems. The digital steps, after preparing the
abutment and preparing the gingival sulcus for impression, are as follows:
1.
Entering patient data into the digital software.
2.
Intraoral scanning (of the preparation, adjacent teeth, antagonists,
and occlusion).
3.
Creating the digital design.
4.
Milling the ceramic block.
5.
Adapting and cementing the restoration.
Fig. 8.2. Entering data into the Romexis software.
Fig. 8.3. Intraoral scanning with the Planscan Planmeca scanner.
Fig. 8.4. The digital model.
Fig. 8.5. The digital design of the crown.
Fig. 8.6. Sending the digital design to the milling machine.
a
b
Fig. 8.7. Ceramic crown a. after milling and b. after glazing and polishing.
Chapter 9.
CEMENTATION OF ALL-CERAMIC RESTORATIONS
The main objective of cementing prosthetic restorations is to achieve a tight seal
between the preparation surface and the restoration. This aims primarily to maintain
pulp vitality and periodontal health and, secondarily, to ensure prosthesis retention. The
bond between the preparation and the restoration involves creating an intimate
adhesion between the preparation, cement, and prosthesis, making it crucial for the
physical properties of the fixing material to align with the intended purpose.
Fifty years ago, dentists had limited choices for restoration materials and
cementation. Over the subsequent decades, there have been significant changes with
the introduction of new materials. Responding to market demand, dental product
manufacturers have developed non-metallic materials with greatly improved esthetic
appearances, mimicking natural tooth aesthetics.
Although zinc phosphate cements have been used in dentistry for over a century,
their low strength, poor aesthetics, complex mixing protocols, potential for sensitivity,
inadequate adhesion, and high solubility make them a poor choice for many
contemporary applications. In response to the heightened expectations of modern
restorations, new categories of cements have been created. Consequently, today's
practitioners are faced with a multitude of restoration materials, bonding cements, and
clinical scenarios, sometimes causing confusion.
Dental cement should ideally possess the physical, biological, mechanical, and
handling properties necessary to ensure restoration retention on the substrate. These
properties include:
•
Biocompatibility with pulp and soft tissues surrounding teeth.
•
Favourable physical properties, such as low solubility, extended working time,
quick setting time, radiopacity, and appropriate film thickness to facilitate proper
seating of the restoration.
•
Mechanical properties, including good adhesion to both substrate and restoration
material, as well as high shear, tensile, and compressive strength.
•
Ease of mixing and removal of excess material.
Classification of cements
All permanent cements can be classified into one of two major categories:
conventional cements and adhesive cements.
Conventional cements achieve retention through mechanical interlocking with
restoration and substrate surfaces. Examples include zinc phosphate cements,
carboxylate cements, glass ionomer cements, and resin-modified glass ionomer
cements. Adhesive cements, on the other hand, provide stronger bonds with
substantially higher adhesive properties, offering increased retention and support for
low-strength restorations.
Glass Ionomer Cements
Glass ionomer cements were developed as a combination of silicate and
polycarboxylate cements to provide fluoride release (from silicate cements) and
adhesion to enamel and, to a lesser extent, dentin (from polycarboxylate cements).
They consist of a powder containing fluoroaluminosilicates and a liquid containing
polyacrylic acid and tartaric acid. When polyacrylic acid reacts with the external surface
of particles in traditional glass ionomer cements, calcium, aluminium, and fluoride ions
are released. Gelation occurs when a significant amount of metal ions is present. The
material continues to harden for an additional 24 hours. Conventional glass ionomer
cements have poor bond strength to tooth structures, moderate compressive strength
(85 to 126 MPa), and low tensile strength (6 to 7 MPa). Because the physical qualities
of traditional glass ionomer cement can vary widely depending on the powder-to-liquid
ratio, proper manufacturer's mixing instructions must be followed. The constant, longterm fluoride release and fluoride recharge capabilities of conventional glass ionomer
cement are considered favourable for caries prevention, but adhesion strength between
traditional glass ionomer cement and dentin is reduced when dentin is too wet,
contributing to post-cementation discomfort. Therefore, wet dentin surfaces must be
dried with cotton before cementation. It has been noted that the solubility of
conventional glass ionomer cement increases with early contamination by water and
saliva, while the final hardness is found to decrease. When working with conventional
glass ionomer cement, a coating agent (e.g., Ketac Glaze, 3M ESPE) or petroleum jelly
should be used to protect the material at the restoration margins. Additionally,
conventional glass ionomer cement exhibits high resistance to acid attack and
bleaching, which may not make it the best choice for individuals with gastroesophageal
reflux disease or those seeking whitening treatment.
Resin-Modified Glass Ionomer Cements
Resin-modified glass ionomer cements combine the chemistry and technology of
both conventional cement and resin. This type of dental cement was created to address
two major deficiencies of conventional glass ionomer cement: early sensitivity to
moisture contamination and high solubility. Resin-modified glass ionomers were
developed by replacing methacrylate monomers with some of the polyacrylic acid in
traditional glass ionomer cements. Compared to conventional glass ionomer cement,
resin-modified glass ionomer cement has demonstrated improved adhesion to tooth
structure, higher compressive strength, and lower solubility, ensuring long-term margin
stability and reduced post-cementation sensitivity while maintaining high fluoride release
comparable to conventional glass ionomer cement. Resin-modified glass ionomer
cements have a low bond strength to tooth substrate (approximately 8 MPa), high
compressive strength (93-226 MPa), and high tensile strength (13-24 MPa). Patients
with restorations cemented with resin-modified glass ionomer cement have shown the
least post-cementation sensitivity compared to those cemented using conventional
glass ionomer or zinc phosphate cements at all time intervals studied in various in vivo
studies. The setting reaction of this cement is a two-stage process involving an acidbase reaction and polymerization. Once the powder and liquid are combined, an acidbase reaction occurs, resulting in the formation of polyacrylic salt. Polymerization can
be initiated either by light or by enough free radicals.
Resin Cements
In the mid-1970s, resin cements were introduced as an alternative to acid-base
reaction cements. Bisphenol-A-glycidyl methacrylate (Bis-GMA) resin, as well as other
modified methacrylates from composite resin, is used to create resin cements. These
cements have a polymerization-based setting reaction.
Advantages of resin cements include excellent compressive and tensile strength,
strong adhesion, low solubility, and adequate aesthetics. These characteristics allow
them to be used in cases where retention is a concern, as well as for low-strength
restorations or when aesthetics need to be considered (e.g., glass ceramic and
composite resin restorations). Some resin cements incorporate filler materials like
ytterbium trifluoride or aluminium and barium fluorosilicate, which can release fluoride
after setting. This suggests that resin cement may have cariostatic properties. For all
cementation applications, self-curing and dual-curing resin cements can be used. Resin
cements that are light-cured should only be used for glass ceramic veneers or minimally
invasive restorations with a thickness under 0.8 mm. According to some manufacturers,
dual-curing resin cement improves long-term color stability. Without using light curing,
dual-curing resin cement has been found to have lower bond strength and
microhardness. Therefore, it is essential to light-cure all dual-curing resin cements for
an adequate period at all accessible restoration margins.
Resin cements can be classified based on their bonding mechanism, namely total
etch, self-etch, and self-adhesive. Total etch systems generally involve three steps: acid
etching, rinsing, and gentle drying. Then, bonding agents are applied and cured,
followed by the application and bonding of the resin cement.
In a self-etch system, the first two steps are replaced by a self-etch bonding agent
that combines conditioner, primer, and adhesive. Self-adhesive resin cements were
created and debuted in 2002 to improve ease of use. Despite the fact that this category
of resin cements does not really have a long clinical history, it is already the most
preferred.
The first product, RelyX Unicem from 3M ESPE, has been thoroughly researched
and is widely used worldwide. To maximize their effectiveness, such cements do not
require surface pre-treatment or bonding agents. As a result, compared to traditional
resin cements, the sensitivity of the technique in cementing with self-adhesive resin
cement has been substantially reduced, but the adhesion is also lower than in the case
of adhesive cements. The translucency of this type of cement is good, being available in
chromatic shades for different clinical circumstances.
Polymer degradation over time is still a problem with resin-containing dental
cements (adhesive resin cement and resin-modified glass ionomer).
Indications of different cements for indirect restorations
The lifetime of a restoration is strongly influenced by the selection of the dental
cement or the inappropriate handling of the chosen material. Clinicians must select
dental cements based on physical, mechanical, aesthetic, and handling characteristics,
as well as cost and method requirements.
Due to the different composition and characteristics, cement selection and
cementation technique is extremely important for the long-term clinical success of allceramic restorations.
In the dental medicine of the last decades, a marked evolution has been highlighted
at the level of bonding agents, adhesive systems and resin cements. The adhesion
mechanism is quite different for dentine and enamel.
Cements have been developed to achieve a bond with the organic phase of dentin
through the dentinal adhesion system.
Cements that adhere to the organic phase of dentin using the dentin adhesion
system are called "resin cements" or "composite resin cements". These adhesion
systems are based on the formation of a hybrid layer with the collagen fibers of the
dentine structure.
All glass ceramic restorations must be demineralized with hydrofluoric acid, then
treated with a silane-based primer, bonding agent and resin cement. High-strength
ceramic restorations with zirconium oxide or aluminium oxide infrastructure are not acid-
etched and therefore cannot be bonded. To fix this type of restorations, it is necessary
to use a surface treatment, which includes sandblasting, the application of silanes and
special primers.
There is no ideal dental cement that meets all biomechanical requirements. In the
current conditions, when new materials and techniques appear, the cementation of new
types of all-ceramic restorations is no longer a routine act. Knowing the qualities and
drawbacks of each cement, the doctor will choose the type of product that best
corresponds to each clinical situation.
The cements used in dentistry are classified according to several criteria: the
adhesion mechanism, the adhesion system, respectively the polymerization
mechanism.
9.1 CLASSIFICATION OF CEMENTS ACCORDING TO THE ADHESION
MECHANISM
v Polycarboxylate cement, glass ionomer (hybrid ionomer)
v Resin cement
v Resin modified glass ionomer cement [RMGICs]
v Dimethylacrylate cement - with/without microfilling
9.2. CLASSIFICATION OF CEMENTS ACCORDING TO THE ADHESION
SYSTEM:
v Adhesion to the tooth surface through the adhesion system of enamel and dentin
v Adhesion using a metallic primer
v Adhesion to the ceramic restoration by treating the ceramic surface with a silane
coupling agent.
9.3 CLASSIFICATION OF DENTAL CEMENTS BASED ON THE POLYMERIZATION
MECHANISM:
v Light-cured cements
v Chemically cured (self-cured) cements
v Dual-cure cements (auto- and light-cured).
Table 9.1. Classification of resin cements based on the polymerization mechanism
Classification of resin cements based on polymerization mechanism
Resin
Cement
Light-Cured
Polymerization
Method
Photo-initiators
activated by light
Dual-Cured
Chemical reaction
and light
Self-Cured
Chemical reaction
between two
materials
Characteristics
Indications
❖ Extended working ❖ Esthetic restorations
time
❖ Non-metallic
❖ Chromatic stability restorations
❖ Translucent ceramics,
thin ceramic layer
❖ Strong adhesion ❖ Opaque ceramics
❖ Aesthetic
❖ Non-metallic
❖ Easy to use
restorations
Used in areas where
❖ Metallic restorations
light curing is
❖ Endodontic posts
challenging
9.3.1 Light-Cured Resin Cements
These utilize photo initiators activated by light. The ability of light to penetrate all
areas and activate photo initiators is crucial for this type of cement.
An advantage of light-cured cements is the improved working time compared to
other types of cements.
Their chromatic stability is compared to that of dual-cured or self-cured resin
cements. These cements are suitable for non-metallic restorations.
Light-cured resins are recommended when cementing fully ceramic restorations
with reduced thickness and translucency, allowing light transmission to reach the resin
cement, or non-metallic orthodontic appliances and non-metallic immobilization devices.
Some common light-cured cements include:
v RelyX™ Veneer Cement (3M ESPE, www.3MESPE.com)
v Variolink® Esthetic Dual LC (Ivoclar Vivadent Inc.)
v Choice™ 2 Light-Cured Veneer Cement (BISCO, Inc.)
v Calibra® (Dentsply Caulk, Milford, DE)
v Nexus®2 (Kerr Corporation, Orange, CA), Illusion™ (Bisco, Inc)
v Insure® (Cosmedent, Inc, Chicago, IL).
9.3.2 Dual-Cured Resin Cements (Auto-Light Polymerizable)
These can be activated through chemical means and light. They are
recommended when the ceramic is too thick or too opaque to allow light transmission
through the restoration. Dual-cured cements are used for any non-metallic restoration
where there is a question about the ability of light to fully penetrate and quickly seal the
margins.
Examples of dual-cured cements include:
v NX3 Nexus® Third Generation (Kerr Corporation)
v RelyX™ Ultimate Resin Cement
v Variolink® Esthetic Dual (Ivoclar Vivadent Inc.)
v Panavia V5 (Kuraray America, Inc)
v Bistite II DC (J. Morita USA, Inc, Irvine, CA)
v Duo-link™ (Bisco, Inc).
9.3.3 Self-Cured Resin Cements
These polymerize through a chemical reaction and are called self-cured. To
initiate this polymerization reaction, the two pastes that make up the cement must be
mixed.
They are especially useful in areas where light polymerization is difficult, where
light cannot penetrate, such as metallic restorations or metal-ceramic restorations,
metallic endodontic posts, and ceramic restorations with a thickness > 3mm, which can
result in a lack of light penetration.
Some of these types of resin cements include:
v Panavia™ (Kuraray Dental, www.kuraraydental.com)
v C&B™ Cement (BISCO, Inc, Schaumburg, IL)
v MultiLink® (Ivoclar Vivadent, Inc, Amherst)
v C&B Metabond® (Parkell, Inc, Farmingdale, NY).
9.4. CLASSIFICATION OF RESIN CEMENTS ACCORDING TO THE ADHESIVE
SYSTEM
The adhesive system can be:
v total-etch (total-demineralizing)
v self-etch (self-demineralizing)
v self-adhesive
Table. 9.2. Classification of Resin Cements According to the Adhesive System
Classification of Adhesive Cements by Adhesive Scheme
Resin Cement
Adhesive Scheme
Characteristics
Total-Etch
Demineralization with 30%-40%
phosphoric acid, followed by
adhesive application
❖ Excellent cement-to-tooth bond
strength
❖ Reduced microleakage
❖ Good long-term predictability
❖ Technique requires multiple
steps
Classification of Adhesive Cements by Adhesive Scheme
Resin Cement
Adhesive Scheme
Characteristics
Self-Etch
Self-demineralizing primer, followed
by pre-mixed cement application
❖ Easy to use
(AutoDemineralizing)
Auto-Adhesive
❖ Good bond strength
❖ Less error-prone technique
Single component, phosphoric acid
is included in the resin
❖ Capable of bonding to the
surface of an untreated tooth
❖ "Selective demineralization" can
be incorporated to enhance bond
strength
9.4.1 Total-Etch Resin Cements
These cements use the technique of acid etching of enamel and dentin with 3040% phosphoric acid. This demineralization procedure removes the smear layer, and
dentinal tubules are opened. After demineralization, the adhesive is applied to the
preparation to bond the cement to the tooth.
These cements and the adhesives used with them can be either light-cured or
dual-cured.
Total-etch resin cements have significantly increased the bond strength of resinbased cements and reduced microleakage significantly.
This category ensures the best cement-to-tooth bond but involves the most steps
for bonding ceramics, composite resins, or metals to the tooth.
This multi-step technique is complex and can compromise bonding effectiveness
because each stage represents a potential source of e
rror.
9.4.2 Self-Etch Resin Cements
Self-etch systems use a self-etching primer to prepare the tooth surface, and the
pre-mixed cement is applied over the primer. The bonds with dental structures using
these cement categories are almost as good as those of total-etch cements.
Self-etch cements are popular among dentists because they are easy to use.
However, these cements have shown weaker enamel bond strength compared to
total-etch systems. Therefore, total demineralization, the three-step adhesive system
established over 30 years ago, still represents the gold standard in terms of versatility
and durability.
Resin cements incorporating self-etching primers reduce clinical steps, increase
ease of handling, reduce the risk of operating errors, and sensitivity to the technique.
It is imperative to follow the manufacturer's instructions during cementation with
adhesive cement because researchers have discovered incompatibilities between dualcure resin cements and simplified adhesive systems.
9.4.3 Auto-Adhesive Resin Cements
Auto-adhesive cements are single-component systems that have good bond
strength to dentin, enamel, and ceramics without the need for separate bonding agents.
These cements can adhere to an untreated tooth surface that has not been
prepared or pre-treated with a demineralizing agent, primer, or bonding agent, allowing
cementation in a single step. These cements contain phosphoric acid, which is
introduced into the resin. Once mixing is initiated, phosphoric acid reacts with filler
particles and dentin in the presence of water, forming a chemical bond. The resin is
polymerized into a polymer, as is the case with composite resin adhesion.
In the case of some cements in this category, enamel adhesion is improved when
a demineralizing agent and adhesive agent are applied. This "selective
demineralization" approach uses a demineralizing or self-demineralizing primer before
applying the auto-adhesive resin cement. "Selective demineralization" of enamel and/or
dentin surfaces and indirect restorations can improve the adhesion of auto-adhesive
resin cements.
Unlike the results obtained on enamel, when dentin is demineralized with phosphoric
acid and a bonding agent is applied before cement application, the bond strength
decreases. This negative effect of pre-demineralizing dentin for self-etch adhesives has
been repeatedly documented in the literature. When tested without predemineralization, self-adhesive resin cements have proven to produce fairly strong
bonds to dentin. Examples of auto-adhesive cements include:
v RelyX™ Unicem (3M ESPE)
v TheraCem® (BISCO, Inc.)
v Maxcem Elite™ (Kerr Corporation)
v SpeedCEM™ (Ivoclar Vivadent Inc.).
Resin-based cements: composition, properties, manipulation
Resin-based cements are composed of diacrylic resins and glass filler. They usually
have a dual-polymerization mechanism. There are two types of "traditional" resin
cements: those commonly used - dual-cure cements, and photopolymerizable cements.
The most recent addition to the "family of resin cements" is the self-etching cements,
which require tooth surface pre-treatment and can have many clinical advantages.
Resin-based aesthetic cements require a binder for adhesion to the tooth and a
primer for adhesion to the ceramic surface.
Adhesive cements usually only require a binder for adhesion to the tooth. These
cements should be selected when stronger adhesion and high mechanical strength
values of ceramics are desired.
Auto-adhesive cements are composed of diacrylic resins (with acidic and adhesive
groups) and glass filler. They contain adhesive components that eliminate the need for a
separate acid etching agent, primer, or bonding agent for adhesion to dental structures
or zirconium oxide-based ceramics. Some products recommend the use of a silane
primer for silica-based ceramics and a ceramic primer for zirconium oxide.
Auto-adhesive cements have a dual polymerization mechanism. During
polymerization, auto-adhesive cements change their pH from acidic (pH 2-3) to neutral
(pH 5-6). The initial acidity allows them to etch dentin and adhere to dental structure.
The physical properties of resin cements are under the standardization of the
International Organization (ISO) standard No. 4049, which sets strict requirements for
these cements. When selecting a cement, the requirement that the cement must comply
with the standard is a good step in the final decision. This standard requires a minimum
strength of 50 MPa and radiopacity equivalent to aluminum. At this moment, no other
cement can meet the requirements imposed on resin cements.
Systems range from the simplest to relatively complex kits
designed for aesthetic restorations (ceramic veneers).
For adhesion to dentin, alloys, and silicon substrates, specific
bonding agents are available. Without these specific bonding agents,
cements exhibit moderate adhesion strength to dentin. The use of
bonding agents and primers is essential to achieve optimal results.
Photopolymerizable cements have the highest adhesion
capacity, are the most stable, and achieve the highest degree of
conversion. In cases where we do not have the ability to penetrate
the light source, self-adhesive resin is a better choice than dual-cure
resin. For many of the cements used for veneer cementation,
manufacturers provide the material primarily as a photopolymerizable
material, with the option to add a dual-cure catalyst only if needed.
Because all resin cements use dimethacrylates, the materials
polymerize into densely cross-linked polymers that are highly
resistant to moisture absorption, insoluble in oral fluids, and have
high durability. Resin cements are similar to composite restorative
materials but with low filler particle concentrations (50% to 70%).
For proper use, pure resin cements require surface pretreatment of the tooth with 37% phosphoric acid and the application
of a dentin bonding agent before applying the resin cement. These
cements form a micromechanical bond both with the tooth structure
on one side and with the restorative material on the other.
Primers improve the adhesion between resin-based cements and
various restorative materials and can be classified based on the
substrate (glass ceramics, alumina, zirconia, alloys) they are
designed for. Silanizing agents are used for glass ceramics
(feldspathic ceramics, leucite-reinforced ceramics, lithium disilicate).
Modern silanizing agents are available in single-bottle systems and
have a longer shelf life.
Ceramic primers based on acidic adhesive monomers are used
with alumina and zirconia-based ceramics. The acidic adhesive
monomer used in CLEARFIL CERAMIC PRIMER (Kuraray America,
Inc) is a phosphoric acid ester known as 10 MDP. This primer also
contains silane. It works on any type of ceramic.
To extend the shelf life, an ethanol-based solvent is used.
Metallic primers based on sulfuric methacrylates are used for
cementing metal restorations. Some primers contain multiple active
agents and can be used on multiple surfaces.
Self-adhesive cements are available in capsule or automix syringe
form.
The capsule system works better for cementing a single unit, such
as a crown or inlay. Cementing multiple units or a bridge can pose
problems because it requires multiple capsules. Some manufacturers
have tried to produce larger single doses available for cases with
multiple units. The best solution for larger cementations is the
automix syringe. It allows control over the amount of cement
dispensed while the tip distributes it mixed and ready for use.
Material loss is minimal with this device.
For the cementation of endodontic posts, manufacturers have two
delivery options. One uses an elongation cannula for single-dose
capsules, and the other uses a tip extension for automix syringes.
Many types of prosthetic restorations can be successfully
cemented using self-adhesive resin cements, including metal crowns,
all-ceramic pressed crowns, inlays, and onlays (including leucite
ceramics, reinforced leucite, lithium disilicate, alumina, or zirconia
oxide restorations), and metal-ceramic crowns.
No cement will provide the optimal level of longevity without
proper preparation, which includes good resistance and shape
retention. Self-adhesive resins and resin cements, due to increased
adhesion, can help compensate for minor issues such as excessive
axial inclination or inadequate preparation height. However, no
cement will secure the restoration in the long term when the
preparation is inadequate.
Mechanisms of Adhesion of Cements to
Ceramic Adhesion to Glass Ceramic
Generally, restorations made from feldspathic ceramic and leucitereinforced ceramic should be cemented with resin-based cements,
either adhesive or aesthetic. These are recommended due to their
superior mechanical properties and strong adhesion to dental
structures compared to other cements.
Resin-based adhesive cement significantly improves fracture
resistance and marginal sealing of restorations compared to selfadhesive cement and zinc phosphate.
Glass Ceramic Pretreatment Technique
Normally, glass ceramic is pre-treated with hydrofluoric acid gel
before silanization. Hydrofluoric acid etches the ceramic surface, and
the etching time is crucial for each category of ceramic material (20
seconds, 60 seconds, and 90 seconds).
Adhesion to Zirconia Oxide
Zirconia is a non-glass ceramic, so it doesn't etch using traditional
methods. The retention of zirconia-based ceramics depends on the
mechanical abrasion of the surface and chemical bonding with an
adhesive monomer from special primers or cements. An adhesive
monomer, such as 10 MDP, adheres to zirconia-based ceramics. The
phosphate ester group in the acid monomer results in a chemical
bond to metal oxides (the oxidized surface of alloys) of zirconiabased ceramics and other ceramics. Therefore, it is effective to use
resin-based adhesive and self-adhesive cements that include
adhesive monomers for cementation. In the case of aesthetic resinbased cements, pre-treatment with a ceramic primer containing
adhesive acid monomers is necessary.
Zirconia Oxide Pre-treatment Techniques
Among the techniques for promoting adhesion to zirconia-based
ceramics, we mention sandblasting and tribochemical silica coating.
These pre-treatments are used before using a silane-based
adhesive, ceramic primer, adhesive cement, or self-adhesive.
If a ceramic primer, adhesive cement, or self-adhesive containing
an acidic adhesive monomer is used, the easiest method of surface
abrasion for ceramics is sandblasting. Tribochemical silica coating
creates a bond between silica and the treated surface through a
chemo-mechanical reaction. After completing this reaction, the
surface is salinized to achieve a chemical bond with it.
The adhesion strength of resin-based cements (PANAVIA F
2.0/Kuraray America, Inc., RelyX ARC/3M ESPE, RelyX Unicem/3M
ESPE) to Lava/3M ESPE has been improved by sandblasting and
applying primer to the surface compared to leaving it untreated.
Some studies have also shown that tribochemical silica coating
(Rocatec Soft/3M ESPE) was better than sandblasting with 60 µm
aluminum oxide. Tribochemical coating resulted in superior bond
stability.
A good method for promoting a chemical bond to zirconia-based
ceramics is the use of a 10 MDP primer. Silanes cannot form a
chemical bond with zirconia without containing acidic adhesive
monomers such as 10 MDP.
When resin-based cements are used, the internal surface of the
restoration needs to be treated differently depending on the type of
material (metal, ceramic, zirconia oxide).
The enamel/dentin surface will need treatment with phosphoric
acid, while the restoration surface will be treated with hydrofluoric
acid, sandblasting, or silanization, depending on the type of
restoration.
Surface treatment for different ceramic materials is presented in
Table 9.3
Surface treatment
of the crown
Chemical treatment
of the crown
Glass-containing ceramics
(feldspathic, reinforced with leucite,
lithium disilicate)
Zirconia
( 3 si 5 mol % yttria )
After the try-in stage, cleaning with
special solutions (Ivoclean,
Zirclean), and then etching with 5%
HF for 90 seconds (feldspathic), 60
seconds (leucite-reinforced), 20-30
seconds (lithium disilicate)
Application of silane primer (pure
silane or ceramic primer) and
drying
After the try-in stage,
sandblasting with aluminum
oxide 50 µm, 10 seconds at 1
bar (5% mol yttria) or 2 bars (3
mol% yttria).
Applying 10 MDP primer (pure
MDP, ceramic primer, or
universal adhesive), and then
drying.
Resin-based adhesive cements
Advantages, disadvantages, and clinical considerations
The physical properties of resin cements are standardized under
International Organization for Standardization (ISO) standard No
4049, which establishes strict requirements for these cements. This
standard calls for a minimum strength of 50 MPa and radio-opacity
equivalent to aluminium.
Resin cements offer various solutions in many clinical situations.
Systems range from the simplest to relatively complex kits designed
for aesthetic restorations (ceramic veneers). There are two types of
"traditional" resin cements: those that are commonly used - dual-cure
cements, and those that are light-cured.
Photopolymerizable cements produce the highest bond strength,
are the most stable, and achieve the highest degree of conversion.
Due to their chemical complexity, dual-cure systems have a
lower conversion rate and the shortest lifespan. In cases where it is
not possible to access a light source, self-adhesive resin is a better
choice than dual-cure resin. This is reflected in the fact that for many
of the cements intended for aesthetic purposes, manufacturers make
the material primarily available as a light-curing material, with the
option to add a dual-cure catalyst only if necessary.
Since all resin cements use dimethacrylates, the materials
polymerize into dense cross-linked polymers that are highly resistant
to moisture absorption, insoluble in oral fluids, and have high
durability.
For proper use, pure resin cements require surface pre-treatment
of the tooth with 37% phosphoric acid and the application of a dentin
bonding agent before applying the resin cement. These cements
form a micromechanical bond both with the tooth structure on one
side and with the restorative material on the other side.
There are two types of "traditional" resin cements: those that are
commonly used - dual-cure cements and light-curable cements.
The most recent addition to the "resin cement family" is selfdemineralizing cements that require pre-treatment of the tooth
surface and can offer many clinical advantages.
The capsule system works better for cementing a single unit,
such as a crown or an inlay. Cementing multiple units or a bridge can
pose challenges because it requires more capsules. Some
manufacturers have attempted to produce larger single doses
available for cases involving multiple units.
The best solution for larger cementation procedures is the
automix syringe. This allows for precise control of the amount of
cement dispensed, while the tip delivers it pre-mixed and ready for
use. Material wastage is minimal with this device.
Because self-adhesive cements undergo dual polymerization,
they are suitable for the cementation of endodontic posts as well.
Many types of prosthetic restorations can be successfully
cemented using self-demineralizing resin cements, including metal
crowns, all-ceramic pressed crowns, inlays and onlays (including
leucite ceramic, leucite-reinforced, lithium disilicate, alumina, or
zirconia restorations), and metal-ceramic mixed crowns.
It's important to note that, in general, the bond strength of selfdemineralizing resin cements is not as high as that of resin cements
using the total-etch technique.
New primers for metal and ceramics have emerged that have
improved the bonding strength of cements to non-demineralized
substrates, such as zirconium oxide and metal.
Self-demineralizing adhesives and resin cements, thanks to their
increased adhesion, can help compensate for minor issues such as
excessive axial convergence of abutments or the absence of
adequate axial height in the preparation. However, no cement will
provide long-term fixation when the preparation is inadequate.
An ideal bonding material should meet numerous requirements,
including good sealing properties, durable adhesion to both the tooth
and the restoration, sufficient mechanical strength, low viscosity,
resistance to disintegration, tissue compatibility, and ease of
handling.
It is important that the use of a new cement is based on scientific
evidence and a good understanding of the chemical and physical
mechanisms of the cement. This should be followed by a study of the
manufacturer's recommendations for the indicated steps, as new
products often require procedures that may not be familiar to the
practitioner. These new cements are often technique-sensitive, and
incorrect application of the cement can lead to the failure of
restorations.
The requirements of an ideal cement used for cementing
prosthetic restorations in routine practice are: biocompatibility,
interface sealing, anticariogenic properties, adhesion and strength,
radiopacity, viscosity and film thickness, solubility, and aesthetics.
Glass ceramics (feldspathic, leucite-reinforced, lithium disilicate)
should be cemented with adhesive resin cement or esthetic resinbased cement, using appropriate primers and bonding agents.
Due to their increased strength, zirconia-based ceramics can be
cemented with adhesive cements or traditional cements. Selfadhesive cements are easier to use than traditional ones. When
better retention is required, zirconia restorations can be cemented
with dual adhesive or aesthetic cements, using appropriate primers
for both the tooth and ceramic.
Table 9.4 presents the indications for different cements based on
the prosthetic restoration material.
Material
restoratio
n
Zirconia
Lithium
disilicate
Ceramics
reinforced
with
leucite
Treatment RPF
Cement type
Cementing
conventional
: only at restorations
with
Retention mechanics
good
Glue: cement resin
self- adhesive
Tooth
preparation
Cleaning preparation
( paste and brushing)
Cleaning preparation
( paste and brushing )
Good insolation
Cleaning preparation
( paste and brushing )
Diga insolation
Glue: cement adhesive
Acid engraving
on
phosphoric and / or
resin base
bonding
conforming instructions
manufacturer
Glue: cement selfCleaning preparation
adhesive
( paste and brushing )
based on resin
Rubberdam insolation
Cleaning preparation
Glue: cement adhesive ( paste and brushing )
on
rubberdam insolation
resin base
Acid engraving and / or
bonding
Conforming instructions
manufacturer
Cleaning preparation
( paste and brushing )
Glue: cement adhesive Rubberdam insolation
on
Acid engraving
resin base
and / or bonding
conforming
instructions manufacturer
Sandblasting (aluminum oxide
50-60 µm, <2 bars) application of
RMGI or SARC cement.
Sandblasting (aluminum oxide
50-60 µm, <2 bars), Applying
primer 10 MDP and then dual
self-adhesive cement
Sandblasting (aluminum oxide
50-60 µm, <2 bars) ,Applying 10
MDP bonding primer and then
dual resin cement
5% HF acid etching for 20
seconds, applying silane primer,
and then SARC cement.
5% HF acid etching for 20
seconds, applying silane primer
,Applying bonding agent,
applying ARC cement
9.6% HF acid etching for 1
minute (maximum 2.5 minutes),
applying silane primer, applying
bonding agent, and applying dual
resin cement.
Resin
nanocera
mics
Cleaning preparation
( paste and brushing )
Glue: cement adhesive rubberdam insolation
on
Acid engraving and / or
resin base
bonding
Conforming instructions
manufacturer
Sandblasting(aluminum oxide 2550 µm, 1.5-2 bars), applying
bonding agent, and then dual
resin cement.
How to choose a dental cement based on the clinical situation?
In everyday practice, we encounter various clinical situations that require
different operative protocols. Ideal situations are those in which the preparation margins
are located supragingival. Other factors such as the restorative material and clinician
preferences affect the choice of cement in many cases.
The ability to clinically isolate the working area from contamination due to the
presence of blood and other oral fluids is absolutely essential for the successful use of
total-etch resin cements. Some dental materials cannot be cemented without the use of
adhesive techniques due to the nature of the ceramic material, for example, pressed
ceramic and lithium disilicate. Resin cements and total-etch techniques represent the
technique and material for definitive cementation, providing optimal results in terms of
sealing and retention of the restoration. Clinical timelines must be strictly adhered to for
therapeutic success.
Cementing ceramic veneers with light-curable resin cement like RelyX
Veneer by 3M ESPE
Procedure:
v The ceramic veneer must be etched with hydrofluoric acid. This
step is sometimes performed in the dental laboratory before the
restoration is sent to the dental office. If it hasn't been done in the
laboratory, the etching should be done in the dental office, following
the protocol specific to the ceramic material, after the veneer trial
has been completed.
v If a provisional restoration has been previously applied, it should be
removed. Then, the tooth should be cleaned using a fluoride-free
pumice paste, followed by rinsing thoroughly with water and gently
drying it.
v Applying the dental dam.
v Matrices are placed between the teeth to prevent unwanted
adhesion of adjacent teeth.
v The bonding area between the teeth is isolated, and Teflon tape is
used if necessary to prevent contamination.
v The final restoration is checked for both aesthetic and positional
aspects. For this purpose, the veneer is placed with the translucent
shade of the try-in paste (RelyX Try-in Paste).
v If the restoration meets all criteria, the veneer is removed,
thoroughly washed, both the tooth and the veneer are dried, and
the adhesive step is initiated.
v Saliva decontamination can be achieved using 35% phosphoric
acid for 15 seconds, or with ethanol in an ultrasonic bath, or with
special pastes (Ivoclean, Zirclean). Afterward, rinse and dry the
veneer.
v The hydrofluoric acid etching should only be done if it has not been
performed in the laboratory.
v A single layer of silane primer is applied to the bonding surface of
the veneer and allowed to dry.
v Phosphoric acid is applied to the enamel and dentin for 15
seconds.
v It is rinsed for 10 seconds.
v Using a separate applicator for each layer, two coats of universal
adhesive are applied to both the enamel and dentin.
v It is gently dried for 2-5 seconds.
v It is not photopolymerized!
v A single layer of adhesive is applied to the silanized surface of the
veneer.
v It is gently dried for 2-5 seconds.
v It is not photopolymerized!
v The previously selected shade of cement is applied to the veneer.
v The veneer is placed with slight pressure.
v It is photopolymerized for 2 seconds, and excess cement is
cleaned from the margins.
v Each area and margin of the veneer is photopolymerized for 40
seconds.
v The margins and adaptation are rechecked.
Cementing zirconia crowns with self-adhesive cement like RelyX U200
Working procedure
v Removal of temporary restoration and cleaning of the prepared
tooth.
v Applying the rubber dam.
v The inner surface of the ceramic crown is sandblasted, cleaned,
and dried.
v The cementing material component is applied to the mixing pad.
v Mix the cement.
v Apply the cementing material to the prosthetic restoration or on the
prepared tooth.
v Apply the restoration, polymerize with light, and remove excess.
Self-adhesive resin cement demonstrates good adhesion to both enamel and
dentin, easy manoeuvrability, a low risk of postoperative hypersensitivity, and easy
excess removal.
Clinical stages of bonding ceramic restorations
Treating the internal surface of the prosthetic restoration by sandblasting, only for
zirconia.
-
Etching with hydrofluoric acid only for glass ceramics.
-
Silanization - 1 minute, gentle drying, storage in the dark, monocomponent
silane (silane + alcohol / acetone) or bicomponent (+ aqueous solution, must
be applied after a few hours)
-
Applying the adhesive agent, compatible with the cement used
Surface dental treatment
-
Cleaning with non-fluoridated abrasive paste
-
Bicarbonate air-polishing jet (air-flow).
-
Applying orthophosphoric acid (gel, not solution) 30-40% (30
seconds on enamel, 15 seconds on dentin to prevent collagen fiber
collapse and compromise adhesion
-
Rinsing off the acid agent, gentle drying for 10 seconds.
-
Applying the primer to the dentin substrate for 30 seconds, then
drying
-
Applying the adhesive agent to the hard dental tissues
-
Applying resin cement inside the full ceramic FPD (Fixed Partial
Denture) and positioning it at the level of the dental preparation.
-
Pre-polymerization (using a curing light) until the bonding agent
reaches a gel-like consistency.
-
Removal of excess cement and complete photopolymerization on
all surfaces for 60-90 seconds (ceramic absorbs 40-50% of the light
emitted by the curing light; when ceramic thickness is > 0.7mm, a
dual-cure cement is chosen).
Conclusion
Dental prosthetics undergoes radical transformations with the advent of the
digital era. From digital impressions to digital data manipulation for diagnosis and
treatment planning, and to the production of CAD/CAM restorations, the way dental
services are provided to patients has undergone a significant shift.
Every day, new materials with biomechanical and aesthetic characteristics
emerge, allowing them to withstand demands even in the most challenging situations.
More studies and time are needed to evaluate the true clinical performance of these
restorations.
Through the continuous development of materials and technologies, the
prosthetic treatment of partial edentulism poses a challenge for clinicians, with the
ultimate goal being to choose the most suitable options for each specific clinical
situation.
To ensure the longevity of fixed prosthetic restorations, it is essential to perform
each procedure with professionalism and responsibility, always keeping the best
interests of the patients, the primary beneficiaries of our treatments, in mind.
Every clinical step is crucial. To successfully complete a prosthetic
restorative treatment, the student must recognize the role of wellacquired theoretical knowledge in formulating an accurate diagnosis,
leading to an appropriate treatment plan. Following the execution of
clinical procedures according to standardized protocols, which have
proven to be essential in therapeutic success, clinical experience will
accumulate and make everything more manageable and predictable.
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