ORAL HISTOLOGY lecture – 4i

THE ENAMEL Enamel is the hardest and most highly mineralized substance of the body Covers the anatomical crown Synthesized by Ameloblasts which are lost after eruption Incapable of repair Enamel varies in thickness over the surface of the tooth and is often thickest at the cusp and thinnest cementoenamel junction (CEJ).

The 3 parts of a tooth: Anatomic Crown Anatomic Root Pulp Chamber The anatomic tooth crown is the portion of the tooth covered by enamel. The anatomic root is the lower two thirds of a tooth. The roots are normally subgingival, buried in bone, and serve to anchor the tooth in position. The pulp cavity houses the dental pulp, an organ of myelinated and unmyelinated nerves, arteries, veins, lymph channels, connective tissue cells, and various other cells involved in formative or developmental, nutritive, sensory, protective, and defensive or reparative processes. Anatomic Root 3

Constituents Inorganic substance (96%) Organic substance (4%) Hydroxyapatite crystal Ca10(PO4)6(OH)2 Organic substance (4%) Water (3%) Organic (1%)

RELATIONSHIP OF ENAMEL & DENTIN DURING TOOTH DEVELOPMENT Ameloblasts Enamel Dentin Predentin Odontoblasts

Structure Formed by rods (prisms) Facts about enamel rods Number varies with tooth type Extends from DEJ to surface Under light microscope they appears hexagonal/Round/oval with surrounded with prism sheath

Function Protect the underlying sensitive dentine and the pulp. Clinical consideration Caries Attrition abrasion erosion enamel pellicle Enamel etching

THE DENTINE Dentin is the dental hard tissue between enamel or cementum and the pulp chamber. It is secreted by the Odontoblasts of the dental pulp It’s a living tissue and yellowish in colour

H&E STAINED SECTION OF A TOOTH Dentin Predentin Odontoblasts Pulp cells

Constituents Inorganic substance (70%) Organic substances (30%) Water (10%) Its harder than bone and cementum and is softer than the enamel and has elasticity

Structure MICROSCOPICALLY It contains dentinal tubules Fact about dentinal tubules Runs from the pulp to DEJ and CDJ Shows branching at the DEJ Contains the odontoblast and nerves

Dental Tissues—Dentin (Tubules)2 Presence of tubules renders dentin permeable to fluoride Number of tubules per unit area varies depending on the location because of the decreasing area of the dentin surfaces in the pulpal direction Dentin Pulp Tubule Odontoblast Cell Nerve Fibers The tubules run parallel to each other in an S-shape course. The tubules are filled with a fluid. External stimuli cause movement of the dentinal fluid, a hydrodynamic movement, which can result in short, sharp pain episodes. These details are important in understanding dentin hypersensitivity. Fluid 12

Dental Tissues—Dentin (Tubules)2 Enamel Association between erosion and dentin hypersensitivity3 Open/patent tubules – Greater in number – Larger in diameter Removal of smear layer Erosion/tooth wear Tubules Exposed Dentin Odontoblast Associations between erosion and hypersensitivity involve: Open/patent tubules Greater in number Larger in diameter Removal of smear layer Erosion/tooth wear Undercalcified Receding Gingiva

Ultra structure of dentine Two zones of dentine can be seen under electron microscope Peritubular dentine Dentine which immediatelly surround the odontoblastic process Its collagen is highly mineralized It contains few organelles in the odontoblastic process Has few nerve fiber

Intertubular dentine cont. Represent the bulk of the dentine Less mineralized than the peritubular dentine High amount of collagen meshwork

Dentinoenamel junction (DEJ) Junction between the enamel and dentine It shows scalloped line with its concave side towards the enamel and the convex side toward the dentine

Dentinal enamel junction DEJ Striae of Retzius

Innervations of the dentine Still debatable Previously postulated that Myelinated nerve arise from the pulp loose their myelin sheath and enter between the odontoblast Recently the electron microscope showed nerve fibers in close relation to the odontoblastic process Clinically dentine is sesitive

Type of dentine Primary dentine: 2. secondary dentine Formed before completion of the apical foramen It include mantle dentine and circumpulpal dentine 2. secondary dentine Formed after completion of the apical foramen and continuous throughout life of the tooth Fewer tubules than the primary dentine There is a bend where primary dentine and secondary dentine meets.

3. Reparative /tertiary dentine Dentine formed in response to injury Its formed under the injured area Characterized by having and more twisted tubules than normal dentine

Clinical consideration Caries and dentine Cavity preparation Heat Chemicals in relation to dentine Note: 1mm2 of dentine damaged destruct approximately 30 thousands living odontoblasts

THE PULP It’s a delicate tissue and highly vascular Derived from the dental papilla (ectomesenchymal) Pulp vitality is gained through blood vessels, nerves and lymphatics

functions Sensory Formative (forms a new dentine) Nutritive Defensive (immune cells) Reparative (deposition of a new layer)

anatomy Pulp chamber- bulk of the pulp sits here Pulp canals – Contains the radicularpulp Extends from the cervical line to the apical foramen Single in anterior and multiple in postrior teeth Apical foramen Passage of blood vessels and nerves The size and locaton of apical foramen is not always at the same place

Microscopic features It Contains Cells intercellular substances Odontoblasts Fibroblast Defence cells Undifferentiated mesenchymal cells intercellular substances ground substances consist of glycoaminoglycan and proteoglycan Collagen fibers are type I &II collagen

blood vessels of the pulp Runs long the long axis of the pulp Has one of the highest blood supply of the body and the flow of the blood is fast Capillaries with fenestration and shows rapid transportation They are from superior and inferior alveolar arteries Blood vessels of the pulp communicates with the periodontal blood vessels, therefore infection can spread between the two

Lymphatic of the pulp Lymphatic vessels exist in the pulp and can be demonstrated by certain histological techniques.

Nerve supply There are two types Unmyelinated nerve Myelinated nerve Belonged to sympathetic (autonomic nervous system and they contrl the blood vesels Myelinated nerve these are for pain Clinically the pulp can interprete pain no matter the stimuli Constitute 90% of the pulp Ri=eaches the cell rich zone and forms the a network of nerve known as parietal layer (plexus of Rschkow) Found in the dentine tubule and a short distance between the odontoblast

Age changes of the pulp With age there is: Increase in connective tissue fibers Dencrease in cells Formation of pulp stones Reduction of the pulp due to continuous deposition of dentine

Pulp stones Types True stones False stones Circular and contains dentinal tubules False stones Do not have dentinal tubules and contains calcified mass of the pulp

Clinical consideration Severe stimuli through cavity preparation might destroy the pulp Irritation material can destroy the pulp Accessory canal are hazardous to root canal filling Pulp caping with zinc oxide or calcium hydroxide increase will lead to repair of the dentine Pulp exposure in young people because the pulp chamber is very wide