Dentin and Dentin Physiology

Dentin is the mineralised tissue that forms the bulk of the tooth, lying beneath the enamel of the crown and the cementum of the root and surrounding the pulp. Unlike enamel it is a living, tubular tissue maintained by cells of the adjacent pulp, and the fluid in its tubules links its mechanical behaviour to sensitivity and to the response of the tooth to stimuli.

Definition

Dentin is the hydrated, tubular, partly mineralised connective tissue that constitutes the main mass of the tooth, formed and maintained by odontoblasts at its pulpal surface and permeated by fluid-filled dentinal tubules.

Scope

This entry covers dentin's composition, tubular structure, permeability, and its physiological connection to the pulp (the pulpo-dentin complex). It describes the hydrodynamic basis of dentin sensitivity as a mechanism. It is a reference description and does not prescribe management of sensitivity or other conditions.

Core questions

• How does dentin differ from enamel in composition and structure?
• What are dentinal tubules and why does dentin permeability matter?
• How is dentin connected physiologically to the dental pulp?
• What is the proposed mechanism linking dentin to sensitivity?

Key concepts

• Dentinal tubules
• Odontoblasts
• Pulpo-dentin complex
• Dentin permeability
• Hydrodynamic mechanism of sensitivity
• Tubule occlusion
• Smear layer

Mechanisms

Dentin is about 70% mineral by weight, with a substantial organic matrix (mainly type I collagen) and water, making it tougher and more deformable than enamel and a supportive base that resists crack propagation from the brittle enamel above (He & Swain, 2008). It is penetrated by dentinal tubules that run from the pulp toward the enamel-dentin junction; these tubules contain fluid and processes of the odontoblasts that line the pulp, so dentin and pulp function as a single pulpo-dentin complex. The number and patency of tubules determine dentin permeability, which governs the movement of fluid and substances across the tissue (Pashley, 1986; Pashley et al., 1992). Movement of tubule fluid in response to thermal, osmotic, or tactile stimuli is the basis of the hydrodynamic explanation of dentin sensitivity, and occluding the tubules reduces both permeability and sensitivity (Pashley, 1986).

Clinical relevance

Because dentin is living, permeable, and continuous with the pulp, its exposure and its permeability are central to how teeth respond to wear, restorative procedures, and sensitivity. This entry explains those mechanisms for orientation and is not a basis for treating sensitivity or any condition in an individual.

History

The tubular nature of dentin has been recognised since early microscopy, but the modern physiological understanding - dentin as a permeable tissue continuous with the pulp, whose fluid movement explains sensitivity - was substantially developed in the late twentieth century, with Pashley's work on permeability and tubule occlusion central to that account (Pashley, 1986; Pashley et al., 1992).

Key figures

• David H. Pashley

Seminal works

• pashley-1986
• pashley-1992

Frequently asked questions

Is dentin a living tissue?

Yes. Unlike enamel, dentin is maintained by odontoblasts whose cell bodies sit at the pulp surface and whose processes extend into the dentinal tubules, so dentin and pulp behave as one functional unit and dentin can respond to stimuli over time.

Why does exposed dentin sometimes feel sensitive?

The widely cited hydrodynamic explanation holds that stimuli cause fluid in the dentinal tubules to move, which in turn excites nerves in the pulp; reducing tubule patency tends to reduce this sensitivity. This describes a proposed mechanism, not a treatment recommendation.