Dental Anatomy: Dentin Overview

Dentin Overview

• Dentin is the hard tissue forming the bulk of a tooth.
• It protects the tooth's pulp.
• It supports the tooth's enamel.

Dentin-Pulp Complex

• Dentin and pulp are embryologically, histologically, and functionally related.

Types of Dentin

• Coronal dentin
• Radicular dentin
• Primary dentin
• Secondary dentin
• Tertiary dentin

Primary Dentin

• Consists of mantle dentin and circumpulpal dentin.

Tertiary Dentin

• Also known as reparative dentin or reactive dentin.
• Formed in response to damage or stimulation.
• Produced by cells that are directly affected.

Sclerotic Dentin

• Similar refractive indexes
• Response to stimuli such as caries, attrition, abrasion, cavity preparation or erosion.
• Appears white in transmitted light and black in reflected light.
• Collagen fibres and apatite crystals appear in the dentinal tubules.

Intratubular Dentin

• A hypermineralised ring of dentin.
• Found within the dentinal tubule. -It is (40%) more mineralised compared to intertubular dentin.

Intertubular Dentin

• Major body of dentin.
• Located between dentinal tubules.

Interglobular Dentin

• Areas of hypomineralised/unmineralised dentin.
• Found in tooth crowns.
• Mineralisation pattern is mainly globular.

Dentinogenesis

• Primary dentin can be of two types.
• Mantle dentin occupies the peripheral area where the basement membrane was earlier present.
• Circumpulpal dentin is the remaining larger segment of dentin.

Odontoblast Differentiation

• Important for understanding the formation of normal and reparative dentin.

Mantle Dentin Formation

• Odontoblasts differentiate from ectomesenchymal cells.
• Secrete collagen (type III) into existing ground substance of dental papilla.
• Collagen fibrils are large (0.1-0.2µm) and called von Korff's fibres.
• These fibres intermingle with aperiodic fibrils (type VII collagen).
• They sit at right angles to the basal lamina.

Matrix Vesicles and Crystal Formation

• Odontoblasts release matrix vesicles containing calcium, phosphate, alkaline phosphatase, and calcium-binding lipids, enabling hydroxyapatite crystal formation within the vesicles.

Dentin Tubule Course, Extent, and Diameter

• Dentinal tubule course is generally S-shaped curve, called primary curvature.
• They make a double curve, starting perpendicular to the pulpal surface and ending perpendicular to the DEJ and CDJ
• Extent: crown - DEJ to pulp and root - CDJ to pulp
• Tubules are longer than the thickness of dentin.
• Diameter: 2.5μm near the pulp, and 1.2μm in the mid portion, and 900μm near the DEJ.

Dentin Tubule Density and Branching

• Tubules are farther apart in the periphery and closer near the pulp.
• Tubules per unit area in the pulpal surface are 50,000-90,000.
• Major and more frequent branching is in the root compared to the crown.

Secondary Dentin

• Formed after root formation is complete.
• A narrow band bordering the pulp.
• Fewer tubules than primary dentin.
• Different from primary dentin and has a boundary between it and primary dentin.

Reparative Dentin

• Reaction to various stimuli including abrasion, erosion, and caries.
• Odontoblasts are killed and replaced by migrated undifferentiated cells.
• This forms the reparative dentin.

Dead Tracts

• Odontoblastic processes are lost and the empty tubules are filled with air
• Can be caused through various procedures.

Contour Lines of Owen

• Disturbed matrix and mineralisation process results in hypocalcified areas.
• Accentuated incremental lines that are a result of coincidence of neighbouring dentinal tubules

Neonatal Line

• Found in deciduous and permanent first molars.
• Shows an abrupt change in environment, occurring at birth.

Tomes Granular Layer

• In dry ground sections, a granular zone adjacent to cementum in transmitted light.
• Increase in amount occurs from the CEJ to the root apex.
• Produced by coalescing and looping of terminal portions of dentinal tubules.

Predentin

• Located adjacent to pulp tissue. -~2-6µm wide
• Unmineralised dentin.

Chemical Composition

• 70% inorganic content is hydroxyapatite crystals that are smaller than enamel.
• Other inorganic components are phosphates, carbonates, sulfates, and fluoride.
• 20% organic content consists of collagen types I, III, V. and other non-collagenous proteins and lipids.
• Water makes up approximately 10%.

Non-Collagenous Proteins

• Amelogenins
• Dentin Phosphoprotein (DPP)/ Phosphoryn.
• Dentin Sialoprotein (DSP).
• Dentin Glycoprotein (DGP).

Dentin Sensitivity

• There are 3 theories related to pain transmission through dentin.
• Direct Neural Stimulation
• Fluid/Hydrodynamic Theory
• Transduction Theory

Contents of Dentinal Tubules

• Odontoblastic process
• Dentinal fluid (dental lymph)
• Lamina limitans
• Peritubular dentin
• Nerve endings (predentin and inner dentin)

Clinical Considerations

• 1mm² of exposed dentin contains 30,000 cells that could be damaged.
• It's important to seal exposed dentin with non-irritating insulators against bacteria, drugs, undue operative trauma, thermal changes, and irritating restorative materials.

Spread of Caries

• The tubular system undermines the enamel at the DEJ.
• It enables invasion of microorganisms.
• Dentin sensitivity is not a symptom of caries unless the pulp is affected.

Trauma from Operative Instruments

• Trauma may result in odontoblast aspiration.
• Reparative dentin formation occurs in the subodontoblastic layer.

Age Changes

• Dentin vitality, reparative dentin, dead tracts, and sclerotic dentin undergo modifications.

Age and Dentin Vitality

• Odontoblasts are an integral part of dentin.
• Dentin reacts to physiologic and pathologic stimuli.
• Dentin is laid down throughout life.