8. Morphology of tooth dentin. Classification and layers in dentin. Dentin physiology – metabolism, sensitivity and functions. Characteristics of the dentin in primary and permanent teeth in childhood.

MORPHOLOGY AND PHYSIOLOGY OF DENTIN

Main Morphological unit of Dentin is Dentinal Tubule and Structural Unit is Apatite Crystal (Hydroxyapatite)

Morphology of Dentin

Composition of Dentin:

• Organic Substance:
• 25-30% from its weight
• About 90% collagen fibres
• About 10% ground substance
• Inorganic Substance:
• 70-75% from its weight
• Hydroxyapatite crystallites

Dentinal Tubules

• Dentinal Tubules are formed around the odontoblastic process during Dentinogenesis
• Odontoblastic outgrowth is located inside the canal
• Dentin around the tubule is the most mineralized and is called peritubular
• Dentin inbetween the tubule is called intertubular
• Dentin starts from the pulp, intersect all the dentin and reaches the dentin-enamel border
• Above the dental pulp, it is broader and more closely spaced. In the incisor edges and tip of cusps, are parallel to the longitudinal axis of the tooth
• In lateral regions of crown they are oblique
• Dentinal tubules have an S-shaped curves similar to enamel prisms which gives greater strength to structures

Odontoblastic Processes

• It is a Protoplasmic Extension of Odontoblasts
• Odontoblasts remain involved in periphery of the pulp.
• Inside of the odontoblastic process is included microtubules, microfilaments, macrovesicles which all help to prepare for protein synthesis

Peritubular Dentin

• Dentin at the Periphery of each dentinal tubule is called peritubular
• Peritubular is absent in the predentin because predentin is still dentinal matrix without mineralization
• Tubular walls are still not formed but peritubular dentin is most mineralized form of dentin
• When carious lesions or abrasion develops, as a defence mechanism, intertubular dentin can fill the entire lumen of tubule and this dentin layer is called transport or sclerotic dentin

Intertubular Dentin

• Largest mass of dentin is located between the canals
• It is relatively less mineralized than peritubular dentin. Collagen fibrils of organic matrix form a network, over which are situated perpendicular oriented apatite crystals

Layers in Dentin

1. Mantle Dentin
2. Interglobular Dentin
3. Circumpulpal Dentin
4. Predentin
5. 1. Mantle Dentin just below the dentinoenamel junction forms from preexisting ground substance of dental papilla

• Most superficial and most highly mineralised layer of dentin. Mineralization close to that of enamel
• Due to the predominance of Korff’s fibres which are arranged in parallel
• Helps in the tight arrangement of crystals with the smallest inter crystal spaces
• Organic Matter is in its least amount here

2. Interglobular Dentin

Used to describe areas of hypo-mineralized dentin where globular zones of mineralization (calcospherites) have failed to fuse into homogenous mass within mature dentin

Seen in circumpulpal dentin just below the mantle dentin