Dentinal Tubules Structure and Formation

Dentinal Tubules

• The number ratio of dentinal tubules per unit area on the pulpal and outer surfaces is 4:1.
• Dentinal tubules are closely packed together at the pulpal surface than the outer surface.
• The diameter of dentinal tubules is narrower at the outer surface (1 micron) than the pulpal surface (2-3 microns).
• The course of dentinal tubules from the pulp surface to the outer surface takes an S shape, called primary curvature.
• In the root portion and under the tip of the cusp or incisal edge, the dentinal tubules take a straight course.

Odontoblastic Process and Periodontoblastic Space

• The odontoblastic process is also known as Tomes' fiber.
• Periodontoblastic space is the space between the odontoblastic process and the wall of dentinal tubules.
• This space results from the looping of the terminal portions of dentinal tubules, which is a result of different orientation of odontoblastic process.

Interglobular Dentine

• Interglobular dentine appears in the crown just below mantle dentine, and sometimes in the root dentine.
• It results from the incomplete fusion of calcified globules.
• Dentinal tubules cross the interglobular dentine without hindrance.

Mechanism of Attachment between Enamel and Dentine

• The dentino-enamel junction (D.E.J.) is scalloped in shape, providing a mechanical junction.
• The firm union between enamel and dentine is due to the collagen fiber bundles of mantle dentine projecting beyond the D.E.J. and becoming continuous with the organic substance of dentino-cemental junction.

Innervations of Dentine

• Dentine is sensitive, and the most sensitive area is at the D.E.J.
• The response to any stimuli is pain.
• Pulpal nerves (free nerve endings) pass between the odontoblasts and enter the dentinal tubules.

Theories of Dentine Sensitivity

• Direct neural stimulation theory: explains that dentine contains nerve endings that respond when dentine is stimulated.
• Odontoblastic transduction theory: explains that odontoblasts serve as receptors and are coupled to the nerve in the pulp.
• Fluid or hydrodynamic theory: explains that the tubular nature of dentine permits fluid movement to occur within the tubules when stimulus is applied.

Dentine Development

• Odontoblasts differentiate from the peripheral short columnar dental papilla cells with many stubby processes.
• The cells grow in length (40u) and are closely packed together.
• Dentine formation has two stages: matrix formation and maturation (mineralization).

Types of Dentine

• Mantle dentine: the first formed dentine layer in the crown and root.
• Circumpulpal dentine: the remaining primary dentine after mantle dentine is formed.

Reparative Dentine

• Osteodentine: a type of reparative dentine with entrapped cells.
• Atubular dentine: a type of reparative dentine without dentinal tubules.
• Vasodentine: a type of reparative dentine with entrapped blood vessels.

Secondary Dentine

• Regular secondary dentine: formed in response to mild stimuli, such as slow attrition and caries.
• Irregular secondary dentine: formed in response to severe stimuli, such as abrasion and erosion.
• Clinically, regular secondary dentine increases the time taken by caries to reach the pulp, making the liability of pulp exposure during cavity preparation much less likely to occur.