Lect.1 1st stage
Dental Anatomy
Dr. Ameer AL-Ameedee
Functions of Molars:
The permanent molars, like the premolars:
(a) play a major role in the mastication of food (chewing and grinding to pulverize).
(b) are most important in maintaining the vertical dimension of the face (preventing the jaws from closing too
far, which could reduce the vertical dimension between the chin and the nose, resulting in a protruding chin and a
prematurely aged appearance).
(c) important in maintaining continuity within the dental arches, thus keeping other teeth in proper alignment.
(d) molars have at least a minor role in esthetics or keeping the cheeks normally full or supported. You may
have seen someone who has lost all 12 molars (six upper and six lower) and has sunken cheeks.
(e) The loss of a first molar is really noticed and missed by most people when it has been extracted. More than
80 mm of efficient chewing surface is gone; the tongue feels the huge space between the remaining teeth; and during
mastication of coarse or brittle foods, the attached gingiva in the region of the missing molar often becomes abraded
and uncomfortable. Loss of six or more molars could even lead to problems in the jaw joints (temporomandibular
joints or TMJ).
The pulp:
The terminology and essential features of the pulp chambers and pulp canals are considered before presenting
the details of pulp chambers and canals using sectioned tooth specimens. The use of the term pulp chamber, pulp
cavity, or coronal pulp to designate that part of the crown normally filled with soft tissue varies with the anatomist;
however, as with the terms root pulp and radicular pulp, and pulp canal and root canal, it is probably a matter of
professional preference, because a good case can be made for each of the terms. These two sets of terms relating to
crown and root are used as if they have the same meaning, with the recognition that arguably there may be
contextualized differences.
Pulp, Chamber, and Canals:
The embryonic layers are distinct from each other and give rise to specific tissues such as:
The crown and root portion of a tooth that contains the pulp tissues has been arbitrarily divided into the pulp
chamber and the root or pulp canal. The dental pulp is the soft tissue component of the tooth. It occupies the internal
cavities of the tooth (i.e., the pulp chamber and pulp canal). In general, the outline of the pulp tissue corresponds to
the external outline form of the tooth (i.e., the outline form of the pulp chamber corresponds with the shape of the
crown, whereas the outline form of the pulp canal corresponds with the shape of the roots of a tooth).
The dental pulp within these cavities originates from the mesenchyme and has been assigned a number of
different functions:
1-formative.
2-nutritive.
3-sensory.
4-defensive.
The initial function of the dental pulp is the formation of dentin during the developmental period. The complex
sensory system within the dental pulp controls the blood flow and is responsible for at least mediation of the sensation
of pain. The formation of reparative dentin or secondary dentition (osteoid-like dentin) represents a defensive
response to any form of irritation, whether it is mechanical, thermal, chemical, or bacterial. The reactive dentin is
usually limited to the area of pulpal irritation. Separating reactive changes (response to injury) from purely agingrelated changes may be difficult or impossible to do at this time.
Size of the Pulp Cavity:
1. The size of the pulp chamber depends on the age of the tooth and its history of trauma.
2. Secondary dentin is formed continuously throughout the life of the tooth as a normal process, as long
as the vitality of the tooth is maintained.
3. The formation of secondary dentin is not uniform, because the odontoblasts adjacent to the floor and
roof of the pulp cavity produce greater quantities of secondary dentin than do the odontoblasts
located adjacent to the walls of the pulp cavity.
4. Therefore, the size of the pulp cavity is much larger in a young individual than in an adult and should
be considered before extensive tooth reduction is accomplished, especially in a young person.
5. Various traumatic injuries occur that, if severe enough, will initiate a different type of dentin
formation. Irritation induced or reparative dentin may be formed in response to the carious process,
abrasion, and attrition, as well as to operative procedures. This response is protective but may
ultimately be detrimental in later years, because a finite amount of space is present within the pulp
cavity.
6. The size of the pulp cavity in a given tooth should be compared with that in the other teeth.
Foramen:
1. The neurovascular bundle, which supplies the internal contents of the pulp cavity, enters through the
apical foramen or foramina.
2. As the root begins to develop, the apical foramen is actually larger than the pulp chamber, but it
becomes more constricted at the completion of root formation.
3. It is possible for any root of a tooth to have multiple apical foramina. If these openings are large
enough, the space that leads to the main root canal is called a supplementary or lateral canal.
4. If the root canal breaks up into multiple tiny canals, it is referred to as a delta system because of its
complexity.
Pulp Cavities of the Maxillary Teeth:
MAXILLARY CENTRAL INCISOR
Labiolingual Section
1. The pulp cavity follows the general outline of the crown and root.
2. The pulp chamber is very narrow in the incisal region. If a great amount of secondary or irritationinduced dentin has been produced, this portion of the pulp chamber may be partially or completely
obliterated.
3. In the cervical region of the tooth, the pulp chamber increases to its largest labiolingual dimension.
4. Below the cervical area, the root canal tapers, gradually ending in a constriction at the apex of the
tooth (apical constriction).
5. The apical foramen is usually located near the very tip of the root but may be located slightly to the
labial or lingual aspect of the root.
6. Because of this generalized phenomenon, it has been suggested that the root canal filling should
appear on radiographs to extend no closer than 1 mm from the radiographic apex of the tooth.
However, with the use of an electronic apical locator, the clinician can have more confidence in more
closely reaching the apex without overfilling.
Mesiodistal Section:
1. The pulp chamber is wider in the mesiodistal dimension than in the labiolingual dimension.
2. The pulp cavity conforms to the general shape of the outer surface of the tooth.
3. The pulp cavity then tapers rather evenly along its entire length until reaching the apical constriction.
4. The position of the apical foramen is usually slightly off center from the tip of the root, but some
foramina deviate drastically from the apex of the root.
Cervical and Midroot Cross Sections:
1. The pulp cavity is widest at about the cervical level, and the pulp chamber is generally centered within
the dentin of the root.
2. In young individuals the pulp chamber is roughly triangular in outline, with the base of the triangle at
the labial aspect of the root.
3. As the amount of secondary or reactive dentin increases, the pulp chamber becomes more round or
crescent-shaped.
4. The outline form of the root at the cervical level is typically triangular with rounded corners, but some
are more rectangular or angular with rounded corners.
5. The root and pulp canal tend to be rounder at the midroot level than at the cervical level.
6. The anatomy at the midroot level is essentially the same as that found at the cervical level, just smaller
in all dimensions.
MAXILLARY LATERAL INCISOR
Labiolingual Section :
1. The anatomy of the lateral incisor is similar to that of the central incisor.
2. The pulp cavity of the lateral incisor generally follows the outline form of the crown and the root.
3. The pulp horns are usually prominent.
4. The pulp chamber is narrow in the incisal region and may become very wide at the cervical level of
the tooth.
5. Those teeth lacking this cervical enlargement of the pulp chamber possess a root canal that tapers
slightly to the apical constriction.
6. Many of the apical foramina appear to be located at the tip of the root in the labiolingual aspect,
whereas some exit on the labial or lingual aspect of the root tip.
Maxillary central incisor
Mesiodistal Section
1. The pulp cavity closely follows the external outline of the tooth.
2. The pulpal projections or pulp horns appear to be blunted when viewed from the labial aspect of the tooth.
3. The pulp chamber and root canal gradually taper toward the apex, which often demonstrates a significant
curve toward the distal in the apical region.
Cervical and Midroot Cross Sections:
1. The cervical cross section shows the pulp chamber to be centered within the root.
2. The root form of this tooth shows a large variation in shape.
3. The outline form of this tooth may be triangular, oval, or round.
4. The pulp chamber generally follows the outline form of the root, but secondary dentin may narrow
the canal significantly.
MAXILLARY CANINE
Labiolingual Section:
1. The maxillary canine has the largest labiolingual root dimension of any tooth in the mouth.
2. Because the pulp cavity corresponds closely to the outline of the tooth, the size of the pulp chamber
of this tooth may also be the largest in the mouth.
3. The incisal aspect of the canine corresponds to the shape of the crown.
4. If a prominent cusp is present, a long narrow projection from the pulp chamber (the pulp horn) will
be present.
5. The pulp chamber and incisal third or half of the root canal may be very wide, showing a very abrupt
constriction of the root canal in the apical region, which then gently tapers toward the apex. In other
instances, a root canal may taper evenly from the pulp chamber to the apex of the root.
6. Some canines have severe curves in the apical aspect of the root.
7. The apical foramen may appear to exit at the tip of the root or labially to the apex of the root.
Mesiodistal Section:
1. The pulp cavity is much narrower in the mesiodistal aspect.
2. The dimension and degree of taper of the pulp canal of the maxillary canine are very similar to those
of the central and lateral incisors; however, the cuspid has a much longer root.
3. The pulp cavity gently tapers from the incisal aspect to the apical foramen.
4. A mesial or distal curve of the apical root may be present.
5. The apical foramen may appear to exit at the tip of the root or slightly to the mesial or distal aspect of
the root.
Cervical Cross Section:
1. The shape of the root and pulp cavity is oval, triangular, or elliptical.
2. The pulp chamber and canal are often centered within the crown and root.
Occlusion:
Angle furnished his ‘key to occlusion’ and emphasizes the first permanent molars especially the upper first
permanent molar and considers them to be most constant in taking normal position.
Definition Occlusion means the contact of teeth in opposing dental arches when the jaws are closed (static
occlusal relationships) and during various jaw movements (dynamic occlusal relationships)
To understand occlusion in its broadest sense, it is necessary to consider, in addition to TMJ articulation,
muscles, and teeth, some of the neurobehavioral mechanisms that give meaning to the presence and function of the
masticatory system. Although many of the neural mechanisms mediating interaction between occlusion and thoughts,
sensations, and emotions are complex and often indeterminate, it is possible to suggest strategies that could account
for the variety of responses (physiological and psychological) that occur in function and parafunction.
The “obvious” strategy to compensate for wear of proximal contact areas is mesial migration of the teeth, and
the strategy to compensate for wear of the occlusal surfaces is eruption of the teeth. The strategy for regulating the
contraction of the jaw elevators to achieve a normal resting position of the mandible with a small interocclusal space
is a postural reflex (stretch reflex). The overall strategy for motivation to have access to the muscles of mastication
might be to provide a drive for ingestive processes, especially during the early stages of development of the
masticatory system and maturation of the nervous system—swallowing in fetal life, suckling in the newborn, and
chewing in the young infant.
It appears plausible, at least, that emotion may be important not only as a motivational phenomenon but also
as a reflection of what is agreeable or disagreeable about something that is placed in the mouth, including items not
considered to be food and perhaps even restorations that interfere with function or parafunction.
The extensive “education” of persons through the social media, and through professional dental care and
instructions to patients not only has produced an awareness of the teeth and mouth, but also has coupled these
structures to a sense of health and comfort. The affect involved in such a sense of well-being about oral health involves
part of the same neurobehavioral substrate underlying innate drives, motivation, and emotional states necessary for
biological adaptation and survival of the species. Ingestive processes, which include oral motor responses involved in
mastication, are essential for survival. Functional disturbances of the masticatory system may involve
psychophysiological mechanisms that are related to the teeth and their functions. Therefore, occlusal interferences to
function or parafunction may then involve more than simply contact relations of the teeth; they may involve
psychophysiological mechanisms of human behavior as well.
No scientific evidence is available for making a specific structure or psychophysiological mechanism the sole
cause of TMJ/muscle dysfunction. However, any attempt to negate the role of the teeth in human behavior, including
dysfunction, perhaps is made by those who have not had the opportunity to observe the effect on affect, favorable
neuromuscular response, and elimination of discomfort when appropriate occlusal therapy is rendered.
Unfortunately, neuroscientific evidence to separate the subjective from objective clinical observations has not
lived up to its full potential. Scientific clinical studies in which true cause-and effect relationships can be determined
are difficult to design, especially when such relationships may be indirect, “on-again, off-again,” and significantly
influenced by the observer and other factors under natural conditions.
The occlusion is an important aspect of dentistry. The study and practice of most branches of dentistry should
be based on a strong foundation of knowledge of occlusion. Orthodontics and conservatives restoration are no
exception to these as great many changes occur in the occlusion during these therapy. The operative work should
know what constitutes normal occlusion in order to be able to recognize abnormal occlusion.
Definition Centric relation: is the relation between mandible and maxilla where the condyle in the rear most, upper
and mid most position in the glenoid fossa.
Maximum intercuspation: is the maximum occlusal intercuspation irrespective of condylar position.
Complete intercuspation: is seen when the intercuspal position and retruded position are coincident during
mandibular closure.
Occlusal contacts that prevents this are called premature contacts.
Normal Occlusion :Normal occlusion implies a situation commonly found in the absence of disease. It should include
not only a range of anatomically acceptable values but also physiological adaptability.
Ideal Occlusion :The concept of ideal or optimal occlusion refers both to an aesthetic and physiologic ideal. It includes
functional harmony, stability of masticatory system and Neuromuscular harmony .
Physiologic occlusion :The occlusion that shows no signs of occlusion related pathosis. It may not be an ideal occlusion
but it is devoid of any pathological manifestations in the surrounding tissues.
Traumatic occlusion :The occlusion which produces abnormal occlusal stress which is capable of producing or has
produced an injury to the periodontium.
Therapeutic occlusion : It is a treated occlusion employed to counteract structural interrelationship related to
traumatic occlusion.
Factors and forces that determine tooth position:
1. The alignment of the dentition in the dental arches occur as a result of complex multidirectional forces acting
on the teeth during and after eruption.
2. Equilibrium position of opposing forces that are given by lips and cheeks from outer side and tongue from
inner side determine the (stable) position of the teeth )Hence the labiolingual and buccolingual force are
equal, this is call neutral position).
3. proximal and occlusal contacts are important in maintaining tooth alignment and arch integrity.
4. Mastication causing buccolingual and vertical movement of teeth results in wear of proximal contacts.
5. mesial drifting force helps to keep teeth in contact.
Curve of spee:
The curve of spee given by F. Graf Von Spee in Germany in 1890 It refers to the antero-posterior curvature of
the occlusal surfaces beginning at the tip of the mandibular cuspid and following the buccal cusps of bicuspid and
molar continuing as an arch through the condyle.
Class I: most common [maxillary mesiofacial cusp located in the mesiofacial developmental groove of the
mandibular first molar].
Class II: posterior positioning of mandible to maxilla.
Class III: anterior positioning of mandible to maxilla.
Periodontal structures depend on functional occlusal forces to activate the periodontal mechanoreceptors in
the neuromuscular physiology of the masticatory system. Occlusal forces stimulate the receptors in the periodontal
ligament to regulate jaw movements and the occlusal forces. Without antagonists the periodontal ligament shows
some non-functional atrophy. Tooth mobility is the clinical expression of the viscoelastic properties of the ligament
and the functional response Tooth mobility can change due to general metabolic influences, a traumatic occlusion and
inflammation. Premature contacts between the arches can result in trauma to the periodontal structures.
A traumatic occlusion on a healthy periodontium leads to an increased mobility but not to attachment loss.
In inflamed periodontal structures traumatic occlusion contributes to a further and faster spread of the inflammation
apically and to more bone loss. A traumatic occlusion, as in a deep bite, may cause stripping of the gingival margins. It
is not clear if prematurities or steep occlusal guidance contribute to the occurrence of gingival recession. On implants,
prematurities may result in breakdown of osseointegration. In some cases occlusal corrections will be necessary to
eliminate the traumatic influence of a nonphysiological occlusion.
Types of canal configurations occurring in one root.
ROOT CANALS (PULP CANALS) Root canals:
(pulp canals) are the portions of the pulp cavity located within the root(s) of a tooth. Root canals connect to
the pulp chamber through canal orifices on the floor of the pulp chamber, and pulp canals open to the outside of the
tooth through openings called apical foramina (singular foramen) most commonly located at or near the root apex.
The shape and number of root canals in any one root have been divided into four major anatomic configurations or
types. The type I configuration has one canal, whereas types II, III, and IV have either two canals or one canal that is
spilt into two for part of the root. The four canal types are defined as follows:
Type I—one canal extends from the pulp chamber to the apex.
Type II—two separate canals leave the pulp chamber, but they join short of the apex to form one canal apically
and one apical foramen.
Type III—two separate canals leave the pulp chamber and remain separate, exiting the root apically as two
separate apical foramina.
Type IV—one canal leaves the pulp chamber but divides in the apical third of the root into two separate canals
with two separate apical foramina.
Accessory (or lateral) canals also occur, located most commonly in the apical third of the root (Fig. 8-3A and
B) and, in maxillary and mandibular molars, are common in the furcation area.