NEET MDS Lessons
Dental Anatomy
MANDIBULAR FIRST MOLAR
It is the first permanent tooth to erupt.
Facial Surface:- The lower first permanent molar has the widest mesiodistal diameter of all of the molar teeth. Three cusps cusps separated by developmental grooves make on the occlusal outline The mesiobuccal cusp is usually the widest of the cusps. The mesiobuccal cusp is generally considered the largest of the five cusps. The distal root is usually less curved than the mesial root.
Lingual: Three cusps make up the occlusal profile in this view: the mesiolingual, the distolingual, and the distal cusp which is somewhat lower in profile. The mesiobuccal cusp is usually the widest and highest of the three. A short lingual developmental groove separates the two lingual cusps
Proximal: The distinctive height of curvature seen in the cervical third of the buccal surface is called the cervical ridge. The mesial surface may be flat or concave in its cervical third . It is highly convex in its middle and occlusal thirds. The occlusal profile is marked by the mesiobuccal cusp, mesiolingual cusp, and the mesial marginal ridge that connects them. The mesial root is the broadest buccolingually of any of the lower molar roots. The distal surface of the crown is narrower buccolingually than the mesial surface. Three cusps are seen from the distal aspect: the distobuccal cusp, the distal cusp, and the distolingual cusp.
Occlusal There are five cusps. Of them, the mesiobuccal cusp is the largest, the distal cusp is the smallest. The two buccal grooves and the single lingual groove form the "Y" patern distinctive for this tooth
Roots :-The tooth has two roots, a mesial and a distal.
Contact Points; The mesial contact is centered buccolingually just below the marginal ridge. The distal contact is centered over the distal root, but is buccal to the center point of the distal marginal ridge.
Roots: Lower molars have mesial and distal roots. In the first, molar, the mesial root is the largest. It has a distal curvature. The distal root has little curvature and projects distally.
Permanent dentition period
-Maxillary / mandibular occlusal relationships are established when the last of the deciduous teeth are lost. The adult relationship of the first permanent molars is established at this time.
-Occlusal and proximal wear reduces crown height to the permanent dentition and the mesiodistal dimensions of the teeth
occlusal and proximal wear also changes the anatomy of teeth. As cusps are worn off, the occlusion can become virtually flat plane. -In the absence of rapid wear, overbite and overjet tend to remain stable.
-Mesio-distal jaw relationships tend to be stable,
With aging, the teeth change in color from off white to yellow. smoking and diet can accelerate staining or darkening of the teeth.
Gingival recession results in the incidence of more root caries . With gingival recession, some patients have sensitivity due to exposed dentin at the cemento-enamel junction.
Curve of Spee.
-The cusp tips and incisal edges align so that there is a smooth, linear curve when viewed from the lateral aspect. The mandibular curve of Spee is concave whereas the maxillary curve is convex.
-It was described by Von Spee as a 4" cylinder that engages the occlusal surfaces.
-It is called a compensating curve of the dental arch.
There is another: the Curve of Wilson. Clinically, it relates to the anterior overbite: the deeper the curve, the deeper the overbite.
PULP
Coronal
Occupies and resembles the crown,
Contains the pulp horns
It decreases in size with age
Radicular
Occupies roots
Contains the apical foramen
It decreases in size with age
Accessory apical canals
PULP FUNCTIONS
Inductive: The pulp anlage initiates tooth formation and probably induces the dental organ to become a particular type of tooth.
Formative: Pulp odontoblasts develop the organic matrix and function in its calcification.
Nutritive: Nourishment of dentin through the odontoblasts.
Protective: Sensory nerves in the tooth respond almost always with PAIN to all stimuli (heat, cold, pressure, operative procedures, chamical agents).
Defensive or reparative: It responds to irritation by producing reparative dentin. The response to stimuli is inflammation.
Histologically the pulp consists of delicate collagen fibers, blood vessels, lymphatics, nerves and cells. A histologic section of the pulp reveals four cellular zones:
Odontoblastic
Cell-free (Weil)
Cell-rich
Pulp core
Tooth development is commonly divided into the following stages: the bud stage, the cap, the bell, and finally maturation. The staging of tooth development is an attempt to categorize changes that take place along a continuum; frequently it is difficult to decide what stage should be assigned to a particular developing tooth. This determination is further complicated by the varying appearance of different histological sections of the same developing tooth, which can appear to be different stages.
Bud stage
The bud stage is characterized by the appearance of a tooth bud without a clear arrangement of cells. The stage technically begins once epithelial cells proliferate into the ectomesenchyme of the jaw. The tooth bud itself is the group of cells at the end of the dental lamina.
Maxillary Second Deciduous Molar.
-The notation is A or J.
-It looks like a first permanent molar
-There are three roots.
-Usually it has four well developed cusps.
-It is somwhat rhomboidal in outline.
-They often have the Carabelli trait.
- the shape the maxillary first permanent molar strongly resembles that of the adjacent deciduous second molar.
TEMPOROMANDIBULAR JOINT
There are three kind of joints:
· Fibrous
Two bones connected with fibrous tissue
Examples
suture (little or no movement)
gomphosis (tooth - PDL - bone)
syndesmosis (fibula & tibia, radius and ulna; interosseous ligament)
· Cartilagenous
Two subtypes:
2a) primary: bone<--->cartilage (costochondral joint)
2b) secondary: bone<-->cartilage<-->FT<-->cartilage<--> bone (pubic symphysis)
· Synovial
Two bones; each articular surface covered with hyaline cartilage in most cases
The bones are united with a capsule (joint cavity)
In the capsule there is presence of synovial fluid
The capsule is lined by a synovial membrane
In many synovial joints there maybe an articular disk
Synovial joints are characterized by the presence of ligaments
Synovial joints are classified according to the number of axes of bone movement: uniaxial, biaxial, multiaxial
the shapes of articulating surfaces: planar, ginglymoid (=hinged), pivot, condyloid
The movement of the joints is controlled by muscles
The temporomandibular joint is a synovial, sliding-ginglymoid joint (humans)
Embryology of the TMJ
Primary TMJ: Meckel's cartilage --> malleus & incal cartilage. It lasts for 4 months.
Secondary TMJ: Starts developing around the third month of gestation
Two blastemas (temporal and condylar); condylar grows toward the temporal (temporal appears and ossifies first)
Formation of two cavities: inferior and upper
Appearance of disk
Bones: glenoid fossa (temporal bone) and condyle (mandible)
Formation and Eruption of Deciduous Teeth.
-Calcification begins during the fourth month of fetal life. By the end of the sixth month, all of the deciduous teeth have begun calcification.
-By the time the deciduous teeth have fully erupted (two to two and one half years of age), cacification of the crowns of permanent teeth is under way. First permanent molars have begun cacification at the time of birth. -Here are some things to know about eruption patterns:
(1) Teeth tend to erupt in pairs.
(2) Usually, lower deciduous teeth erupt first. Congenitally missing deciduous teeth is infrequent. Usually, the lower deciduous central incisors are thefirst to erupt thus initiating the deciduous dentition. The appearance of the deciduous second molars completes the deciduous dentition by 2 to 2 1/2 years of age.
- Deciduous teeth shed earlier and permanent teeth erupt earlier in girls.
- The orderly pattern of eruption and their orderly replacement by permanent teeth is important.
- order for eruption of the deciduous teeth is as follows:
(1) Central incisor.........Lower 6 ½ months, Upper 7 ½ months
(2) Lateral incisor.........Lower 7 months, Upper 8 months
(3) First deciduous molar...Lower 12-16 months, Upper 12-16 months
(4) Deciduous canine........Lower 16-20 months, Upper 16-20 months
(5) Second deciduous molar..Lower 20-30 months, Upper 20-30 months