Pulp

1. Four zones—listed from dentin inward

a. Odontoblastic layer

(1) Contains the cell bodies of odontoblasts.

Note: their processes remain in dentinal tubules.

(2) Capillaries, nerve fibers, and dendritic cells may also be present.

b. Cell-free or cell-poor zone (zone of Weil)

(1) Contains capillaries and unmyelinated nerve fibers.

c. Cell-rich zone

(1) Consists mainly of fibroblasts. Macrophages, lymphocytes, and dendritic cells may also be present.

d. The pulp (pulp proper, central zone)

(1) The central mass of the pulp.

(2) Consists of loose connective tissue, larger vessels, and nerves. Also contains fibroblasts and pulpal cells.

2. Pulpal innervation

a. When pulpal nerves are stimulated, they can only transmit one signal pain.

b. There are no proprioceptors in the pulp.

c. Types of nerves:

(1) A-delta fibers

(a) Myelinated sensory nerve fibers.

(b) Stimulation results in the sensation of fast, sharp pain.

(c) Found in the coronal (odontoblastic) area of the pulp.

(2) C-fibers

(a) Unmyelinated sensory nerve fibers.

(b) Transmits information of noxious stimuli centrally.

(c) Stimulation results in pain that is slower, duller, and more diffuse in nature.

(d) Found in the central region of the pulp.

(3) Sympathetic fibers

(a) Found deeper within the pulp.

(b) Sympathetic stimulation results in vasoconstriction of vessels.

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

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)
 

The periodontium, which is the supporting structure of a tooth, consists of the cementum, periodontal ligaments, gingiva, and alveolar bone. Cementum is the only one of these that is a part of a tooth. Alveolar bone surrounds the roots of teeth to provide support and creates what is commonly called a "socket". Periodontal ligaments connect the alveolar bone to the cementum, and the gingiva is the surrounding tissue visible in the mouth.

Periodontal ligaments

Histology of the Periodontal Ligament (PDL)

Embryogenesis of the periodontal ligament
The PDL forms from the dental follicle shortly after root development begins
The periodontal ligament is characterized by connective tissue. The thinnest portion is at the middle third of the root. Its width decreases with age. It is a tissue with a high turnover rate.

Maxillary Third Permanent Molar

They are the teeth most often congenitally missing

Facial: The crown is usually shorter in both axial and mesiodistal dimensions. Two buccal roots are present, but in most cases they are fused. The mesial buccal cusp is larger than the distal buccal cusp.

Lingual: In most thirds, there is just one large lingual cusp. In some cases there is a poorly developed distolingual cusp and a lingual groove. The lingual root is often fused to the to buccal cusps.

Proximal: The outline of the crown is rounded; it is often described as bulbous in dental literature. Technically, the mesial surface is the only 'proximal' surface. The distal surface does not contact another tooth.

Occlusal: The crown of this tooth is the smallest of the maxillary molars. The outline of the occlusal surface can be described as heart-shaped. The mesial lingual cusp is the largest, the mesial buccal is second in size, and the distal buccal cusp is the smallest.

Root Surface:-The root may have from one to as many as eight divisions. These divisions are usually fused and very often curved distally.

Soft Oral Tissues

Oral Mucosa

The oral mucosa consists mainly of two types of tissues: the oral epithelium, which consists of stratified, squamous epithelium, and the underlying connective tissue layer, known as the lamina propria.  There are three variations of oral mucosa.

A. Oral epithelium

1. Consists of stratified, squamous epithelium.

2. Four layers (Note: Cells mature as they progress from the deepest [basal] layer to the most superficial [cornified] layer) a. Basal layer (stratum germinativum or basale)

(1) A single layer of cuboidal or columnar cells overlying the lamina propria.

(2) Contains progenitor cells and thus provides cells to the epithelial layers above.

(3) Site of cell division (mitosis).

b. Prickle cell layer (stratum spinosum)

(1) Consists of several layers of larger, ovoid-shaped cells.

c. Granular layer (stratum granulosum)

(1) Cells appear larger and flattened.

(2) Granules (known as keratohyaline granules) are present in the cells.

(3) This layer is absent in nonkeratinized epithelium.

d. Cornified layer (stratum corneum, keratin, or horny layer)

(1) In keratinized epithelium:

(a) Orthokeratinized epithelium the squamous cells on the surface appear flat and contain keratin. They have no nuclei present.

(b) Parakeratinized epithelium the squamous cells appear flat and contain keratin; nuclei are present within the cells.

(2) In parakeratinized epithelium, both squamous cells without nuclei and cells with shriveled (pyknotic) nuclei are present.

(3) In nonkeratinized epithelium, the cells appear slightly flattened and contain nuclei.

B. Lamina propria

1. Consists of type I and III collagen, elastic fibers, and ground substance. It also contains many cell types, including fibroblasts, endothelial cells, immune cells, and a rich vascular and nerve supply.

2. Two layers:

a. Superficial, papillary layer

(1) Located around and between the epithelial ridges.

(2) Collagen fibers are thin and loosely arranged.

b. Reticular layer

(1) Located beneath the papillary layer.

(2) Collagen fibers are organized in thick, parallel bundles.

C. Types of oral mucosa

1. Masticatory mucosa

a. Found in areas that have to withstand compressive and shear forces.

b. Clinically, it has a rubbery, firm texture.

c. Regions: gingiva, hard palate.

2. Lining mucosa

a. Found in areas that are exposed to high levels of friction, but must also be mobile and distensible.

b. Clinically, it has a softer, more elastic texture.

c. Regions: alveolar mucosa, buccal mucosa, lips, floor of the mouth, ventral side of the tongue, and soft palate.

3. Specialized mucosa

a. Similar to masticatory mucosa, specialized mucosa is able to tolerate high compressive

and shear forces; however, it is unique in that it forms lingual papillae.

b. Region: dorsum of the tongue.

D. Submucosa

1. The connective tissue found beneath the mucosa . It contains blood vessels and nerves and may also contain fatty tissue and minor salivary glands.

2. Submucosa is not present in all regions of the oral cavity, such as attached gingiva, the tongue, and hard palate. Its presence tends to increase the mobility of the tissue overlying it.

E. Gingiva

1. The portion of oral mucosa that attaches to the teeth and alveolar bone.

2. There are two types of gingiva: attached and free gingiva. The boundary at which they meet is known as the free gingival groove .

a. Attached gingiva

(1) Directly binds to the alveolar bone and tooth.

(2) It extends from the free gingival groove to the mucogingival junction.

b. Free gingiva

(1) Coronal to the attached gingiva, it is not bound to any hard tissue.

(2) It extends from the gingival margin to the free gingival groove.

c. Together, the free and attached gingiva form the interdental papilla.

.F. Alveolar mucosa

1. The tissue just apical to the attached gingiva.

2. The alveolar mucosa and attached gingiva meet at the mucogingival junction .

G. Junctional epithelium

1. Area where the oral mucosa attaches to the tooth, forming the principal seal between the oral cavity and underlying tissues.

2. Is unique in that it consists of two basal lamina, an internal and external . The internal basal lamina, along with hemidesmosomes, comprises the attachment apparatus (the epithelial attachment). This serves to attach the epithelium directly to the tooth.

3. Histologically, it remains as immature, poorly differentiated tissue. This allows it to maintain its ability to develop hemidesmosomal attachments.

4. Has the highest rate of cell turnover of any oral mucosal tissue.

H. Interdental papilla (interdental gingiva)

1. Occupies the interproximal space between two teeth. It is formed by free and attached gingiva.

2. Functions to prevent food from entering the (interproximal) area beneath the contact point of two adjacent teeth. It therefore plays an important role in maintaining the health of the gingiva.

3. Col

a. If the interdental papilla is cross-sectioned in a buccolingual plane, it would show two peaks (buccal and lingual) with a dip between them, known as the col or interdental col. This depression occurs around the contact point of the two adjacent teeth.

b. Histologically, col epithelium is the same as junctional epithelium