Define Dentin and Structure of Dentin

Define dentin. Write about the physical and chemical properties of dentin.

Dentin is the hard tissue portion of the pulp-dentin complex which forms the bulk of the tooth.

Dentin is slightly harder than bone and softer than enamel.
Dentin hardness varies slightly between tooth types and between crown and root dentin.
Dentin is harder in its central part than on its periphery.
The dentin of primary teeth is slightly less hard than that of permanent teeth.
Dentin appears more radiolucent than enamel and more radiopaque than pulp.

Dentin is viscoelastic and subject to slight deformation.
Dentin’s elastic property is important for the proper functioning of the tooth.
The elasticity of dentin provides flexibility and prevents the fracture of the overlying brittle enamel.

Dentin permeability depends upon the potency of dentinal tubules.
Tubular occlusion, smear layer formation, and lack of tubular communication between primary and secondary dentin will result in reduced permeability.
This lessens the sensitivity of dentin.
Dentin permeability increases as the pulp chamber is approached as the number and diameter of the tubules are more per unit area towards the pulp than towards the periphery.

Dentin chiefly consists of collagen fibers with fractional inclusion of Jipids and noncollagenous matrix proteins.
- Collagen fibers contain mainly type I collagen with small amounts of type III and V.
- These fibers are embedded in ground substances of mucopolysaccharides.
- Noncollagenous matrix proteins pack the space between collagen fibrils and accumulate along the periphery of dentinal tubules.
- These proteins regulate mineral deposition and can act as promoters or inhibitors.
- The main content of the ground substance is proteoglycans which prevent the premature mineralization of the organic matrix.
- The matrix also contains growth factors.
Inorganic material – 65%.
- The inorganic content consists of hydroxyapatite which is composed of several thousand unit cells.
- The crystals are plate-shaped and smaller than enamel crystals.
- These crystals are poor in calcium but rich in carbon.
  Dentin also contains small amounts of phosphates, carbonates, and sulfates.

They extend through the entire thickness of the dentin from the dentin enamel junction to the pulp.
They follow an S-shaped path.
They are longer than the dentin and are thick because they curve through the dentin.
The tubule ends are perpendicular to the DEJ and DCJ.
There are more tubules per unit area in the crown than in the tire root.
They have terminal and lateral branches.

The dentin that immediately surrounds the dentinal tubules is called peritubular dentin.
It is a hypermineralized structure.
This is described as a thin, organic membrane high in glycosaminoglycan.

Tooth Dentin Dentinal Tubules Diagram

Dentin is the dentin located between the dentinal tubules.
Dentin is highly mineralized.
Dentin forms the main body of dentin.
About one-half of the volume is organic matrix mainly collagen fibers, which are randomly oriented around dentinal tubules and ground substances of non-collagenous proteins.

They are the cytoplasmic extensions of the odontoblasts.
Dentin extends into the dentinal tubules They are largest in diameter near the pulp.
They are narrow to about half the size of the cell as they enter the tubules.
They are composed of microtubules of 20 pm in diameter and small filaments of 5 – 7.5 pm in diameter.
These odontoblastic processes are divided near the dentin enamel junction and extend into enamel in the enamel spindles.
Their lateral branches extend laterally into adjacent tubules.