Microscopic Structures Of Dentin

Microscopic Structures Of Dentin

Dentinal tubules:

• Odontoblast processes run in canaliculi that transverse the dentin layer and are referred to as dentinal tubules.
• They extend through the entire thickness of the dentin from the DEJ to the pulp.
• These tubules are perpendicular to DEJ and DCJ.
• Near the root tip and along incisal edges and cusps, tubules are almost straight.
• These are tapered structures.
• They are larger in diameter near the pulpal cavity and smaller at their outer ends.
• There are more tubules per unit area in the crown than in the root.
• The dentinal tubules have terminal and lateral branches.
• Lateral branches extend throughout the dentin and are referred to as canaliculi.

Peritubular Dentin:

• The dentin that immediately surrounds the dentinal tubules is termed peritubular dentin.
• Peritubular Dentin is hypermineralized.
• Peritubular Dentin contains little collagen
• Peritubular Dentin is twice as thick in the outer dentin than in the inner dentin.
• Peritubular Dentin constricts the dentinal tubules to a diameter of 1 |im near the DEJ.
• This is described as a thin organic membrane, high in glycosaminoglycan.
• Between the odontoblastic process and the peritubular dentin, a space known as a periodontoblastic space is present.
• In decalcified sections, the tubule diameter appears similar in the inner and outer dentin because of the loss of peritubular dentin.

Sclerotic dentin:

• Sclerotic Dentin describes dentinal tubules that have become occluded with calcified material.
• Sclerotic Dentin can be observed in the teeth of elderly people, especially in the roots.
• Sclerotic Dentin may be found under slowly progressing caries, common in the apical third of the root and in the
  crown midway between the DEJ and the surface of the pulp.
• Sclerotic Dentin is harder than normal dentin- with reduced fracture toughness.
• Sclerotic Dentin crystals are smaller than normal dentin.
• Sclerotic Dentin reduces the permeability of dentin which help to prolong pulp vitality.

Intertubular dentin:

• Intertubular Dentin is the dentin located between the dentinal tubules.
• Intertubular Dentin represents the primary secretory product of the odontoblasts.
• Intertubular Dentin consists of a network of type I collagen fibrils in which apatite crystals are deposited.
• The ground substance consists of non-collagenous proteins.
• Intertubular Dentin is highly mineralized.
• Apatite crystals are formed along the fibers with their long axes oriented parallel to the collagen fibers.

Interglobular dentin:

• Interglobular Dentin is unmineralized or hypo-mineralized dentin.
• Interglobular Dentin is prevalent in Vit.
• deficiency and high exposure to fluoride.
• Interglobular Dentin is mostly seen in circumpolar dentin.
• Dentinal tubules run uninterrupted as no peritubular dentin exists.
• Interglobular Dentin occurs due to a defect of mineralization and not of matrix formation.

Incremental growth lines:

1. The incremental lines of Von Ebner appear as fine lines or striations in dentin.
2. They run at a right angle to dentinal tubules.
3. They represent a normal rhythmic, linear pattern of dentin deposition in an inward and rootward direction.
4. Its course indicates the growth pattern of dentin.
5. The distance between lines varies from 4-8 mm in the crown to much less in the root.
6. The daily increment decreases after a tooth reaches functional occlusion.
7. Another line called contour lines of owen which results from a coincidence of the secondary curvatures between neighboring dentinal tubules.
8. A wide contour line called the neonatal line is seen which separates the dentin formed before birth and that formed after birth.

Granular layer of tomes:

1. A granular appearing area seen in transmitted light in ground sections of root dentin is called a granular layer of tomes.
2. Granular Layer of Tomes is present just below the surface of the dentin where the root is covered by cementum.
3. Granular Layer of Tomes  increases from CEJ to the apex of the tooth.