1. ORAL HISTOLOGY lecture – 4i

2. 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).

3. 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

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

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

6. 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

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

8. 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

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

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

11. 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

12. 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

13. 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

14. 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

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

16. 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

17. Dentinal enamel junction DEJ
Striae of Retzius

18. 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

19. 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.

20. 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

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

22. 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

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

24. 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

25. 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

26. 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

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

28. 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

29. 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

30. 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

31. 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