Types of dentitions:

1. Diphyodont. Teeth develop and erupt into their jaws in two generations of teeth. The term literally means two generations of teeth.

2. Monophyodont. a single generation of teeth.

3. Polyphyodont. Teeth develop a lifetime of generations of successional teeth

4. Homodont. all of the teeth in the jaw are alike. They differ from each other only in size.

5. Heterodont. There is distinctive classes of teeth that are regionally specialized.

Structure

There are 3 pairs

 The functional unit is the adenomere.

The adenomere consists of secreting units and an intercalated duct, which opens, in a striated duct.

An secreting unit can be:

- mucous secreting

- serous secreting

THE SECRETING UNIT

THE CELLS

Serous cells

(seromucus cells=secrete also polysaccharides), They have all the features of a cell specialized for the synthesis, storage, and secretion of protein
 Pyramidal, Nuclei are rounded and more centrally placed,  In the basal 1/3 there is an accumulation of Granular EPR,  In the apex there are proteinaceous secretory granules,  Cells stain well with H & E (red),  Between cells are intercellular secretory capillaries

Rough endoplasmic reticulum (ribosomal sites-->cisternae)
Prominent Golgi-->carbohydrate moieties are added
Secretory granules-->exocytosis
The secretory process is continuous but cyclic
There are complex foldings of cytoplasmic membrane
The junctional complex consists of: 1) tight junctions (zonula occludens)-->fusion of outer cell layer, 2) intermediate junction (zonula adherens)-->intercellular communication, 3)desmosomes-->firm adhesion

Mucus cells

Pyramidal,  Nuclei are flattened and near the base,  Have big clear secretory granules

Cells do not stain well with H & E (white)

Production, storage, and secretion of proteinaceous material; smaller enzymatic component
-more carbohydrates-->mucins=more prominent Golgi
-less prominent (conspicuous) rough endoplasmic reticulum, mitochondria
-less interdigitations
 

Myoepithelial cells

Star-shaped, Centrally located nucleus, Long cytoplasmic arms - bound to the secretory cells by desmosomes, Have fibrils like smooth muscle, Squeeze the secretory cell

One, two or even three myoepithelial cells in each salivary and piece body, four to eight processes
Desmosomes between myoepithelial cells and secretory cells myofilaments frequently aggregated to form dark bodies along the course of the process. The myoepithelial cells of the intercalated ducts are more spindled-shaped and fewer processes
Ultrastructure very similar to that of smooth muscle cells (myofilaments, desmosomal attachments)
 

Functions of myoepithelial cells
-Support secretory cells
-Contract and widen the diameter of the intercalated ducts
-Contraction may aid in the rupture of acinar cells of epithelial origin

Ductal system

Three classes of ducts:
Intercalated ducts

They have small diameter; lined by small cuboidal cells; nucleus located in the center. They have a well-developed RER, Golgi apparatus, occasionally secretory granules, few microvilli. Myoepithelial cells are also present. Intercalated ducts are prominent in salivary glands having a watery secretion (parotid).
Striated ducts

They have columnar cells, a centrally located nucleus, eosinophilic cytoplasm. Prominenty striations that refer to indentations of the cytoplasmic membrane with many mitochondria present between the folds. Some RER and some Golgi. The cells have short microvilli.
The cells of the striated ducts modify the secretion (hypotonic solution=low sodium and chloride and high potassium). There is also presence of few basal cells.
Terminal excretory ducts

Near the striated ducts they have the same histology as the striated ducts. As the duct reaches the oral mucosa the lining becomes stratified. In the terminal ducts one can find goblet cells, basal cells, clear cells. The terminal ducts alter the electrolyte concentration and add mucoid substance.

Connective tissue
Presence of fibroblasts, inflammatory cells, mast cells, adipose cells
Extracellular matrix (glycoproteins and proteoglycans)
Collagen and oxytalan fibers
 

 Nerve supply
The innervation of salivary glands is very complicated. There is no direct inhibitory innervation. There are parasympathetic and sympathetic impulses, the parasympathetic are more prevalent.
The parasympathetic impulses may occur in isolation, evoke most of the fluid to be excreted, cause exocytosis, induce contraction of myoepithelial cells (sympathetic too) and cause vasodialtion. There are two types of innervation: epilemmal and hypolemmal. There are beta-adrenergic receptors that induce protein secretion and L-adrenergic and cholinergic receptors that induce water and electrolyte secretion.

Hormones can influence the function of the salivary glands. They modify the salivary content but cannot initiate salivary flow.

Age changes

Fibrosis and fatty degenerative changes
Presence of oncocytes (eosinophilic cells containing many mitochondria)

Clinical considerations

Role of drugs, systemic disorders, bacterial or viral infections, therapeutic radiation, obstruction, formation of plaque and calculus.

    - Rich capillary networks surround the adenomeres.

MANDIBULAR CUSPIDS

Mandibular canines are those lower teeth that articulate with the mesial aspect of the upper canine.

Facial: The mandibular canine is noticeably narrower mesidistally than the upper, but the root may be as long as that of the upper canine. In an individual person,the lower canine is often shorter than that of the upper canine. The mandibular canine is wider mesiodistally than either lower incisor. A distinctive feature is the nearly straight outline of the mesial aspect of the crown and root. When the tooth is unworn, the mesial cusp ridge appears as a sort of 'shoulder' on the tooth. The mesial cusp ridge is much shorter than the distal cusp ridge.

Lingual: The marginal ridges and cingulum are less prominent than those of the maxillary canine. The lingual surface is smooth and regular. The lingual ridge, if present, is usually rather subtle in its expression.

Proximal: The mesial and distal aspects present a triangular outline. The cingulum as noted is less well developed. When the crown and root are viewed from the proximal, this tooth uniquely presents a crescent-like profile similar to a cashew nut.

Incisal: The mesiodistal dimension is clearly less than the labiolingual dimension. The mesial and distal 'halves' of the tooth are more identical than the upper canine from this perspective. In the mandibular canine, the unworn incisal edge is on the line through the long axis of this tooth.

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.

MANDIBULAR THIRD MOLAR

Facial: The crown is often short and has a rounded outline.

Lingual: Similarly, the crown is short and the crown is bulbous.

Proximal: Mesially and distally, this tooth resembles the first and second molars. The crown of the third molar, however, is shorter than either of the other molars

Occlusal: Four or five cusps may be present. Occlusal surface is a same as of the first or second molar, or poorly developed with many accessory grooves. The occlusal outline is often ovoid and the occlusal surface is constricted. Occasionally, the surface has so many grooves that it is described as crenulated--a condition seen in the great apes

Contact Points; The rounded mesial surface has its contact area more cervical than any other lower molar. There is no tooth distal to the third molar..

Roots:-The roots, two in number, are shorter in length and tend to be fused together. they show a distinct distal curve