THE TRIAL DENTURE
BASE
Rola M. Shadid, BDS, MSc
Trial Denture Assessment on Articulator
1.


Impression surface examination
Fit
Extension

Polished surface examination
Position of lower teeth
position of upper teeth
inclination of polished surface
3.
Occlusal surface
2.


Impression surface examination
1.


2.


Fit
The bases of the trial dentures should be accurately
adapted to the casts so there will be no movement when
finger pressure is applied to occlusal surfaces.
The impression surface should be checked for any sharp
projections, roughness, or excessive undercuts.
Extension
The border regions of the dentures should be shaped to
conform to the depth and width of the sulci on casts.
In the upper jaw the base should be extended posteriorly
to the post-dam cut in the cast, and in the lower jaw over
the retromolar pad.
Polished surface examination
Position of lower teeth
The teeth on a lower denture should be positioned to conform to the crest of
the mandibular ridges. If there are gross discrepancies between the position of
the teeth and the ridge, the teeth may not be in the neutral zone, and could
become the cause of instability in the mouth.
Position of upper teeth
The position of the anterior teeth should be checked in relation to the incisive
papilla,and the posterior teeth according to guidelines in the previous lecture.
Inclination of polished surface
The buccal and lingual aspects of the polished surfaces must converge
occlusally; so that pressure from the surrounding muscles of the cheeks, lips and tongue
contributes to retention rather than displacement., the exception to this is the upper
anterior area where the labial surface of the flange faces upwards and
outwards.
Example of position of lower teeth
Occlusal view of two
lower dentures: (a) the
teeth follow the crest of
the ridge; (b) marked
discrepancies between
the position of the teeth
and the crest of the ridge
are present, suggesting
that the teeth will not be
in the neutral zone.
a
b
Occlusal surface examination
There should normally be bilateral even
contact in the intercuspal position.
Opposing cusped teeth should
interdigitate accurately.
Trial Denture Assessment
in the Mouth
Trial denture assessment in the
mouth
1.
2.
3.
4.
1.
2.
3.
4.
The denture should be assessed individually for:
Physical retention
Stability
Extension of denture bases
Relationship to the neutral zone
The dentures should then be assessed together for:
OVD
CR position
Esthetics
Phonetics
Establishment of the posterior palatal seal
Don’t Overlook Problems
Difficult/impossible to change after
processing
 May require removal, resetting &
re-processing
 Procedures more costly & time
consuming

Physical retention

If the prognosis for the retention in the upper
jaw is good, dislodgment may be difficult.

In lower denture retention is poor because of
the relatively small denture bearing area and
the difficulty in obtaining efficient border
seal.
Physical retention

If the physical retention of an upper trial denture is
not as good as would be expected from the
anatomical conditions existing in a particular patient,
the cause should be identified and, if found to be a
fault in the denture, must be corrected. Denture faults
may include absence of a border seal resulting from:
• Under-extension
• Inadequate width of flange
• Ineffective seal at the posterior border
• Poor fit of the denture base.
Stability

Movement of denture more than 2 mm
suggests lack of stability of the denture.

This could be due to:
Lack of fit of the denture
Displaceability or unfavorable shape of the
denture bearing area
1.
2.
Extension of denture bases
The accuracy with which the denture borders conform
to the depth and width of the sulci must be
determined.
 The all-important posterior extension of the dentures
over the retromolar pad in the lower jaw and to the
post dam seal area in the upper jaw must be checked.
 If marked overextension of the denture flanges is
present, stretching of tissues will occur when the
dentures are inserted and their elastic recoil will cause
denture dislodgment

Overextension of denture bases

if the denture is displaced immediately
after being seated, over-extension should be
suspected. A small degree of over-extension
may cause dislodgement of the denture when
the dentist gently manipulates the lips and
cheeks or when the patient raises the tongue.
Overextension of denture bases

The exact location of such an error can only
be determined by carrying out a careful
examination inside the mouth.
Overextension of denture bases

When over-extension is present in areas
where the visibility is good, displacement of
the sulcus tissues will be seen as the denture
is seated. However, in the lingual pouches,
visibility is poor, so the dentist will have to
make an assessment based on the behavior of
the lower denture as the tongue is moved.
Overextension of denture bases
In the lingual pouches, overextension can be
assessed according to denture behavior
during tongue movement
 When the lower denture is inserted, it should
remain in place when the mouth is half open
and the tongue is positioned so that its tip lies
just behind the lower anterior teeth.

Correction of over-extension

Correction of over-extension is by reducing
the depth of the offending flange. If this is
not carried out, the finished dentures will
traumatize the mucosa in that area and will be
unstable because of the large displacing
forces exerted by the soft tissues.
Under-extension of denture bases
The presence of under-extension is determined
primarily by intra-oral examination, when the depth of
the sulcus will be seen to be greater than that of the
denture flange.
 In the case of the upper denture, however, a
preliminary indication of under-extension will
be given by the existence of poor physical retention.

Correction of any under-extension will
usually entail taking a new impression in
the trial denture
Neutral zone
The positioning of teeth in the neutral zone
is of particular importance in the case of the
lower denture
 When the lower denture is inserted, it should
remain in place when the mouth is half open
and the tongue is positioned so that its tip lies
just behind the lower anterior teeth.

Neutral zone
If displacement of the denture does occur,
the cause must be identified and the denture
modified to correct the instability.
 An area where this difficulty commonly arises
is the lower anterior region where the lip may
exert excessive pressure

Neutral zone



Correction of this type of fault should be carried out
at the chairside so that the effect of the alterations
can be assessed in the patient’s mouth.
The offending teeth may be reset in the correct
relationship to the soft tissues or they may be
removed and replaced with a wax rim which is
shaped with a wax knife until a stable denture is
produced.
The dental technician is then asked to reset the teeth
in the position indicated by the rim.
Neutral zone

When the tongue is relaxed, it should be
able to rest on the occlusal surfaces of the
teeth – a situation which favors retention
of the lower denture
Assessment of the occlusal
vertical dimension
Verify OVD & Interocclusal
Distance
Same techniques used previously
 Critical to measure & feel 2-4 mm of
interocclusal distance
 No tooth contacts during closest
speaking space

Changing OVD
 Effects:
Occlusion
Facial esthetics

• As mandible moves downward
As
the mandible opens (ie. by
(opening or increasing OVD)
increasing the occlusal vertical
• Incisal edge
movesedge
backmoves
dimension)
the incisal
downward
andoverjet
backward. By
• Increases
increasing
the vertical dimension,
• Helpful Angles Class III
more overjet is obtained and there is
• Problemtoward
Anglesmoving
Class IIto a
a tendency
skeletal Class II situation.
Vertical Dimension Alterations




One or both arches may require
change
Made by the laboratory
May require resetting of all teeth
in at least one arch
Height of both anterior &
posterior teeth must be in
harmony
Vertical Dimension Alterations
If only posterior teeth are changed
 Undesired effect on:
 Overbite relationships
 Esthetics
 Balancing contacts
 Assess how changes will affect overall
appearance

Assessment of CR
Position

If a relatively large occlusal discrepancy is
present, the dentist will be able to see this
without any difficulty. However, the
existence of smaller faults may be
deduced from evidence such as slight
tipping or lateral movement of the
dentures as they occlude.

The dentist must approach the problem
with negative attitude.
Methods of occlusal assessment
 Visual
(touch & slide method)
 Patient
perception
The patient should be asked if the dentures are
contacting evenly. Many patients are able to detect
occlusal unevenness which is so slight that it could
be overlooked by the dentist.
Touch & Slide Method
1. Guide the mandible into CR


The patient is guided into centric
relation by a thumb placed on the
anteroinferior portion of the chin
and the index fingers bilaterally on
the buccal flanges of the lower trial
denture.
As tooth contact approaches, the
dentist's index fingers should rise
off the buccal flanges, pressure on
the buccal flanges or stretching the
lip with index fingers will create the
risk of posteriorly displacing the
lower trial denture, then the patient
closes tightly.
2. The patient closes slowly so that the
dentist can observe the initial occlusal
contact.
3. The final occlusal relationship is not so
reliable, as an uneven occlusion may have
been masked by compression of the
mucosa beneath the denture, tipping of
the denture or posturing of the mandible.
4. The ideal occlusal contact is that at first
contact, even maximum intercuspation at
CR without denture shifting or instability
& without pain; and all the teeth that
occluded uniformly on articulator must
have equally uniform contacts in the
mouth
5.Errors in occlusion may prevent
intercuspation of some teeth when the
first contact is made.
6. Further closure will allow the teeth to
slide into CO as tipping of the denture or
deviation of the mandible will occur
What is your management if you found
that CR not coincide with CO?
You need to register new CR, mount on
articulator according to new CR, and then
reset teeth according to this new CR
 This is done either by removing the posterior
teeth from the lower occlusion rim and both
occlusion rims are placed in the mouth and a
new centric relation record is taken; OR
register new CR by applying bite registration
material on occlusal surfaces of lower teeth.

Removing the posterior teeth from
the lower occlusion rim

To register the new centric relation, the posterior
teeth are removed from the lower occlusion rim and
both occlusion rims are placed in the mouth and a
new centric relation record is taken, the closure is
stopped when the anterior teeth have the same
vertical overlap as they had before the posterior
teeth are removed thus the vertical relation of
the two jaws will not be changed *
Apply Minimal Registration
Material on Lower Occlusals

Improves record
accuracy
 Less resistance
during closure
 Reduces chance of
deflection when
checking record
✔
✘
✘
✔
Small Amount of Registration
Material
Opposing cusps should not penetrate
 Cuspal indentations improve accuracy
compared to flat wax rim

Accurate Mounting

Teeth interdigitate
perfectly




No space around the
cusps
Mandibular cast
removed from
mounting ring
Mounting plaster
ground thinner
Cast remounted, using
the new record
Evaluation of the Esthetics
Esthetics
Check:
 Amount of incisal display
 Harmony of the maxillary teeth
with the smile line*
 Accuracy of the midline
Esthetics



During a normal smile, incisal and middle thirds of
maxillary anterior teeth are visible in almost all patients and
the cervical third in approximately half the patients.
The incisal third of the mandibular teeth will be visible in
most patients.
The lower lip is a better guide for the vertical orientation of
anterior teeth than the upper lips. In most patients the
incisal edges of the natural lower canines and the cusp tips
of the lower first premolars are even with the lower lip at
the corners of the mouth when the mouth is slightly open.
When the teeth are above
the lip at the corners of
the mouth, any one or a
combination of the
followings may exist:
1.
2.

the plane of occlusion
may be too high
the vertical overlap of the
anterior teeth may be too
much
When the lower teeth are
below the lip at the
corners of the mouth, the
opposite situations may
exist
Esthetics
a)
b)
c)
This figure shows
reverse smile line
The fig. shows the
midline is slanting to one
side
The dental midline
should coincide with the
midline of the face
Esthetics
Check
 Angle of the occlusal
plane
The errors in location and
inclination of occlusal plane
can cause serious esthetic
problems, in addition to
functional problems and
problems of stability. (The
figure shows errors in occlusal
plane)
Esthetics
Check
 Proper soft tissue profile,
contours
 Lip support
 Display of the vermilion
border
 Correct nasolabial angle
Esthetics
Ask patients for their opinion prior to
voicing your opinion
 Avoids biasing the patient
 May be helpful to have family or friend
attend the wax try-in

Esthetics
If you or the patient have reservations about
appearance
 Resolve prior to final processing
 Never attempt to persuade a patient out
of a concern
 Problems will be yours later, if the
patient does not like the appearance
Evaluation of the Phonetics
Phonetics
 Easier
to assess
 Teeth have replaced bulky rims
 Crowded tongue space can
adversely affect phonetics
Phonetics
 If
have not worn dentures for extended
period
or
 Dramatic changes (Contour, Tooth
Position, Vertical Dimension):
Allow the patient to read a out loud for 510 minutes to assess phonetics and
comfort
Lisping
Non-uniform overjet of
the anterior teeth
 Diastemas between teeth
 Palatal contours
 Diamond-shaped
openings between
incisors

Bilabial sounds (p, b, m)
Causes of defect in these sounds:
 Insufficient support of lips by teeth or
denture base
 Anteroposterior position of anteriors &
thickness of labial flange
 Incorrect OVD
Labiodental (fricative) sounds
(f,v)




F & v are made between the
upper incisors and the the
posterior one third of the lower
lip
Affected by the anteroposterior
position of upper anteriors and
their length
If upper anteriors short, v sound
will be more like an f
If upper anteriors long, f sound
will be more like v
Linguoalveolar sounds
(t,z,s,d,v,L,ch,sh)*




Valve formed by contact of tip of tongue with the
most anterior part of palate or lingual side of
anterior teeth (linguoalveolar)
The upper and lower incisors should approach end
to end but not touch.
Affected by the length of the upper & lower
anterior teeth (including their vertical overlap)
Also affected by horizontal overlap of anteriors ¶
Linguoalveolar sounds

Incisors should approach end to end
relationship
Normal
relationship of
incisors in CR
Relationship of the incisors
during pronunciation of the
sibilants. If the lower incisal edge
is anterior or posterior the
maxillary incisal edge, this
indicates an error in the overjet.
“S” sound
The “s” sound is the most interesting one
because it is influenced by the teeth and
palatal part of maxillary prosthesis.
Clinical experience suggests that s & t can
cause most problems in a prosthodontic
context.
“S” sound




The tip of tongue is placed far forward, coming
close but never touching the upper anteriors (touch
rugae area)
A small sagittal groove is formed in the upper front
part of the tongue for air to escape between the
tongue & alveolus
The tongue dorsum is flat
Mandible will move forward and downward, with
the teeth almost in contact
“S” sound
 Whistle
on “S” sound
 “S” sound sounds as “sh” or “th”
 Causes……
 Management……..
Denture Base Contours
Affect
phonetics,
comfort and
retention
 Should not be
slightly convex
in shape

Convex
Concave
Denture Base Contours
Ensure that the denture base is not unduly
thick or thin
 Excess bulk will impair comfort


Feel between index finger & thumb
Base that is too thin will be weakened

Should not be able to see through
It was concluded that malformation of
the palatal parts of the denture
influenced speech production more
than differences in OVD did.
Establishment of the posterior
palatal seal
CONVENTIONAL APPROACH
After assessing all the previous parameters
there are certain instructions given to the
patients:1. To rinse with an astringent mouth wash
that is remove to stringy saliva that might
prevent clear transfer marking. There are
steps to be followed
2. Location of pterygo maxillary notch is done by
moving the T burnisher posterior to the
maxillary tuberosity until it drops into the
pterygo maxillary notch. This is necessary as
there are times when small depression in the
residual ridge may resemble pterygo maxillary
notch.
3. Identification of posterior vibrating line by
asking the patient to say “AH” in a normal
unexaggerated fashion.
4. Identification of the anterior vibration line. This
is done by asking the patient to say “AH” with
short vigorous bursts (Valsalva Maneuver can
also be used)
PROCEDURE

A line is placed with an indelible pencil
through the pterygomaxillary notch &
extended 3-4 mm antero-laterally to the
tuberosity approximating the mucogingival
junction. The same is done on the opposite
side. This complete the outlining of
pterygomaxillary seal
The posterior vibrating line is marked with an
indelible pencil by connecting the line through
the pterygomaxillary seal with line just drown
demarcating the post palatal seal
 The resin or shellac denture base is inserted into
the mouth & seated firmly to transfer the marks
from the mouth.
 Denture bases are then returned to master casts
to transfer the markings to the master casts.


The base is trimmed until the posterior vibration
line so that it decides the posterior extent of the
denture border.
(A) A T burnisher is used
to palpate for the
hamular process.
(B) Palpating for the
pterygomaxillary notch

Demarcation of
anterior & posterior
vibrating lines in the
patient mouth

Transferring these lines
to denture base


The shape of post palatal seal is like the cupid bow,
because of the projection of the posterior nasal spine.
Kingsley scraper is used to score the cast, the deepest
areas are located on either side of midline, one third the
distance anteriorly from the posterior vibrating line. It
is usually scraped to a depth of approximately 1-1.5 mm
.
The tissue covering the medial palatal raphe
cannot withstand the same compressive force as
the tissue lateral to it; so it is scraped to depth of
approximately 0.5-1 mm within the outline of
cupid bow.
 The scraping tapers to a feather edge as it
approaches the anterior vibrating line.
 Failure to taper the posterior seal leads to tissue
irritation.

Finally………..
Patient Input
Use open ended questions
“How do you like the appearance?”,
rather than
“Don’t the new dentures look great?”
Patient Input
If the patient sounds unconvinced
 ask more questions
 Do not rush this step to save time!

References




Basker’s Prosthetic Treatment of the
Edentulous Patient. Fourth edition.Chapter
13
Boucher's Prosthodontics Treatment for
Edentulous Patients. Twelfth Edition.
Chapter 19
Complete Denture Prosthodontics, 1st
Edition, 2006 by John Joy Manappallil,
Chapter 17
Dalhousie coninual education