Dentin Structure and Properties

Dentin

• Dentin is the primary connective tissue of teeth, forming the bulk of the tooth structure.
• It surrounds and protects the dental pulp.
• Dentin is covered by enamel on the crown and cementum on the root.
• Unlike enamel, dentin is formed and continues to form throughout life, resulting in secondary dentin.

Physical Properties

• Dentin is typically yellowish in color.
• It is highly elastic, allowing it to withstand the forces of chewing without fracturing the brittle enamel.
• Dentin is harder than cementum and bone, but less hard than enamel.
• Dentin is more radiolucent than enamel, and more radiopaque than cementum and bone when viewed by X-ray.

Chemical Composition

• Dentin is 70-75% inorganic substance (apatite crystals).
• The crystallites are smaller than those in enamel.
• The remaining 25-30% is organic substance which includes 18% collagen type I, 0.9% citric acid, 0.2% insoluble proteins, lipids and carbohydrates, and 10% water.

Histological Structure

• The basic unit of dentin is the dentinal tubule.
• Dentinal tubules run through the dentin from the pulp to the enamel.
• Different types of dentin exist with varying degrees of calcification, including mantle dentin, interglobular dentin, peritubular dentin and circumpulpal dentin.

Odontoblasts

• Odontoblasts are cells that create dentin.
• They are arranged in a palisading manner.
• Their shapes vary across different parts of the tooth.
• Odontoblasts have processes called Tomes' fibers that extend into the dentinal tubules.

Dentinal Tubules

• They are closely packed together, more densely packed at the pulpal surface than at the outer surface.
• Their diameter is narrower at the outer surface (1 micron) than at the pulpal surface (2-3 microns).
• Their course generally traces an S-shape from the pulp to the outer surface.
• Near the cusp tips and incisal edges, the tubules are straight.
• Small secondary curvatures are often present along the tubule's course.
• The space between the odontoblastic processes and the walls of the tubules is called the periodontoblastic space.

Peritubular Dentin

• It's the wall of the dentinal tubules surrounding the odontoblastic processes.
• It contains a higher mineral content than other parts of the dentin.
• In decalcified sections, the peritubular dentin appears as translucent rings around the odontoblastic processes.

Intertubular Dentin

• Forms the main body of dentin between the tubules.
• The first layer formed is termed mantle dentin.
• The remaining part of the dentin is termed circumpulpal dentin.

Interglobular Dentin

• A calcified portion of dentin where mineralized globules are not fused together entirely.
• This is an area with an organic matrix that remained uncalcified.

Granular Layer of Tomes

• A continuous layer of granular appearance found adjacent to the cementum layer.

Incremental Lines

• Result from daily deposition of dentin matrix, followed by periods of rest.
• These can show variations in the tooth's growth.
• von Ebner's incremental lines show up as cones on sections, and can become exaggerated under certain conditions (contour lines by Owen).
• Neonatal lines are lines that occur during birth processes and changes in the child's nutrition/environment around that time.

Dentin Sensitivity

• One of the most important aspects of the dentin/pulp complex is its ability to respond with intense pain to stimuli.
• Three main hypotheses exist to explain dentin sensitivity: direct neural stimulation, odontoblast transduction theory, and hydrodynamic theory.

Life Cycle of Odontoblasts

• Odontoblasts are cells of neural crest origin responsible for dentin formation.
• Their development involves stages, with changes in cell shape and arrangement (from cap and early bell stages to production of predentin and the maintenance of primary dentin or entering an quiescent state for future secondary dentin formation).

Dentinogenesis

• Two types of dentin are formed during dentinogenesis: Mantle dentin (thin layer near the DEJ, with linear mineralization) and circumpulpal dentin (bulk of dentin, with globular and mixed mineralization).

Age Changes in Dentin

• Primary dentin is formed during tooth development and growth,
• Age-related changes in primary dentin lead to variations like translucence in some areas and sclerosis.
• Secondary dentin is formed continuously throughout life at a slower rate than primary dentin.
• Different characteristics exist based on the type of stimulus (and resulting rate of formation), like the type of wavy / irregular formation during repair processes. Also changes are noted as stimulus leads to obliteration of the pulp cavity, or partial obliteration of the root canal. -There exists A- Translucent (sclerotic) and B- Dead tracts types of dentin based upon their structure and the formation that cause it (age and stimulation).