NEET MDS Lessons
Dental Anatomy
MANDIBULAR SECOND MOLAR
Facial: When compared to the first molar, the second molar crown is shorter both mesiodistally and from the cervix to the occlusal surface. The two well-developed buccal cusps form the occlusal outline. There is no distal cusp as on the first molar. A buccal developmental groove appears between the buccal cusps and passes midway down the buccal surface toward the cervix.
Lingual: The crown is shorter than that of the first molar. The occlusal outline is formed by the mesiolingual and distolingal cusps.
Proximal: The mesial profile resembles that of the first molar. The distal profile is formed by the distobuccal cusp, distal marginal ridge, and the distolingual cusp. Unlike the first molar, there is no distal fifth cusp.
Occlusal: There are four well developed cusps with developmental grooves that meet at a right angle to form the distinctive "+" pattern characteristic of this tooth.
Contact Points; When moving distally from first to third molar, the proximal surfaces become progressively more rounded. The net effect is to displace the contact area cervically and away from the crest of the marginal ridges.
Roots:-The mandibular second molar has two roots that are smaller than those of the first molar. When compared to first molar roots, those of the second tend to be more parallel and to have a more distal inclination.
MANDIBULAR FIRST BICUSPID
Facial: The outline is very nearly symmetrical bilaterally, displaying a large, pointed buccal cusp. From it descends a large, well developed buccal ridge.
Lingual: This tooth has the smallest and most ill-defined lingual cusp of any of the premolars. A distinctive feature is the mesiolingual developmental groove
Proximal: The large buccal cusp tip is centered over the root tip, about at the long axis of this tooth. The very large buccal cusp and much reduced lingual cusp are very evident. You should keep in mind that the mesial marginal ridge is more cervical than the distal contact ridge; each anticipate the shape of their respective adjacent teeth.
Occlusal: The occlusal outline is diamond-shaped. The large buccal cusp dominates the occlusal surface. Marginal ridges are well developed and the mesiolingual developmental groove is consistently present. There are mesial and distal fossae with pits,
Contact Points: When viewed from the facial, each contact area/height of curvature is at about the same height.
Root Surface:-The root of the mandibular first bicuspid is usually single, but on occasion can be bifurcated (two roots).
INNERVATION OF THE DENTIN-PULP COMPLEX
- Dentine Pulp
- Dentin
- Nerve Fibre Bundle
- Nerve fibres
The nerve bundles entering the tooth pulp consist principally of sensory afferent fibers from the trigeminal nerve and sympathetic branches from the superior cervical ganglion. There are non-myelinated (C fibers) and myelinated (less than non, A-delta, A-beta) fibers. Some nerve endings terminate on or in association with the odontoblasts and others in the predentinal tubules of the crown. Few fibers are found among odontoblasts of the root.
In the cell-free zone one can find the plexus of Raschkow.
The very first histological evidence of tooth development appear during the second month of intrauterine life. Calcification of deciduous incisors begins at 3-4 months in utero.
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.
Time for tooth development
Entire primary dentition initiated between 6 and 8 weeks of embryonic development.
Successional permanent teeth initiated between 20th week in utero and 10th month after birth Permanent molars between 20th week in utero (first molar) and 5th year of life (third molar)
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.