Disturbances to interarch alignment are

a. Excessive overbite where the incisal edge of the maxillary incisors extend to the cervical third of the mandibular incisors

b. Excessive overjet where the maxillary teeth overjet the mandibular teeth by more than 3mm

c. End-to-end relationship: edge-to edge bite where the anterior teeth meet at there incisal edge with  no overjet or overbite; cusp-to bite where the posterior teeth meet  cusp to cusp with no interdigitation

d. Crossbite where the normal faciolingual relationship of the maxillary to the mandibular teeth is altered for the anterior.teeth. the mandibular  tooth or teeth are facial  rather than lingual to the maxillary teeth for the posterior teeth, normal inercuspaton is not seen

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)
 

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.

FUNCTIONS OF PERIODONTIUM

Tooth support
Shock absorber
Sensory (vibrations appreciated in the middle ear/reflex jaw opening)

HISTOLOGIC CHANGES OF THE PULP

Regressive changes

Pulp decreases in size by the deposition of dentin.
This can be caused by age, attrition, abrasion, operative procedures, etc.
Cellular organelles decrease in number.

Fibrous changes

They are more obvious in injury rather than aging. Occasionally, scarring may also be apparent.

Pulpal stones or denticles

They can be: a)free, b)attached and/or c)embedded. Also they are devided in two groups: true or false. The true stones (denticles) contain dentinal tubules. The false predominate over the the true and are characterized by concentric layers of calcified material.

Diffuse calcifications

Calcified deposits along the collagen fiber bundles or blood vessels may be observed. They are more often in the root canal portion than the coronal area.

Histology of the Cementum

Cementum is a hard connective tissue that derives from ectomesenchyme.

Embryologically, there are two types of cementum:
Primary cementum: It is acellular and develops slowly as the tooth erupts. It covers the coronal 2/3 of the root and consists of intrinsic and extrinsic fibers (PDL).
Secondary cementum: It is formed after the tooth is in occlusion and consists of extrinsic and intrinsic (they derive from cementoblasts) fibers. It covers mainly the root surface.

Functions of Cementum

It protects the dentin (occludes the dentinal tubules)
It provides attachment of the periodontal fibers
It reverses tooth resorption

Cementum is composed of 90% collagen I and III and ground substance.
50% of cementum is mineralized with hydroxyapatite. Thin at the CE junction, thicker apically.