Oral histology LO 7 part 2- dentin

70%

Dentin is ——% inorganic mineral. The primary dentin which is a major component of the crown and root: hydroxy apatite crystals.

20%

Dentin is ——% organic collagen fibres and small amounts of protein.

10%

Dentin is ——% water.

Dentinal tubules

Dentin has greater compressive and tensile strengths than enamel. Dentin is readily permeable due to:

Odontoblasts

Dentin is formed by these cells:

peritubular dentin

This type of dentin makes the walls of the dentinal tubules. Highly mineralized (40%).

Intertubular dentin

This type of dentin is between the tubules. Highly mineralized. Main body of dentin.

Mantle dentin

This type of dentin is the outermost layer of dentin, and the first dentin formed. ————— dentin is intertwined with enamel treating a scalloped DEJ for increased adherence.

Circumpulpal dentin

This type of dentin is the layer around the outer pulpal wall. The dentin formed after the mantle dentin. 6-8mm thick in the crown, 2-6mm thick in the root.

Primary dentin

The dentin formed before the completion of the apical foramen and before the functional eruptive phase. Formed more rapidly; more mineralized than secondary dentin. Constitutes the bulk of dentin in the crowns and roots of teeth. Mantle dentin + circumpulpal dentin.

Secondary dentin.

This dentin is formed after the completion of the apical foramen, after the tooth is in clinical occlusion, and in the functional eruptive phase. Formed slower; less mineralized than primary dentin.

Tertiary dentin

This dentin is formed as a result of injury, and has an irregular pattern of tubule.

Sclerotic dentin

Often found in association with chronic injury of caries and is noted as the tooth ages. On this type of dentin, the odontoblastic processes die and leave the dentinal tubules vacant. These hollow dentinal tubules then become retrofilled and finally occluded by a mineralized substance similar to peritubular dentin.

Lines of Von Ebner

Imbrication lines are also called:

Functional occlusion

——————— occlusion signals the rate of formation of dentin to slow down. Prevents the dentin to continue to grow rapidly and therefore obliterate the pulp.

Dead tracks

Dentinal tubules that are empty due to death of the odontoblasts. Pathway for bacteria to the pulp. Rapid penetration of decay with insufficient time for reparative dentin.

Hydrodynamic mechanism.

Changed in the dentinal fluid.

-evaporation/loss of dentinal fluid

-movement of the fluid

-ionic changes in the fluid.

Changes in dentinal fluid are transmitted to afferent axons present in some tubules, sending a message from the pulp of pain. This is a theory that explains dentinal hypersensitivity.

Narrow

With increased age, the diameter of dentinal tubules ————— because of deposition of peritubular dentin .

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