Enamel and Dentine Histology

Enamel is composed of 96% inorganic minerals (primarily calcium hydroxyapatite), minority carbonate and fluoride, and 4% organic material (collagen, water, some proteins).

Enamel structures include enamel rods (prisms), interrods, crystallites (calcium hydroxyapatite), incremental lines, prismless enamel (rod-less), and the enamel-dentine junction (EDJ).

Enamel rods (prisms) are tightly packed structures with a 'keyhole shape' in cross-section. Each rod contains millions of crystallites and are formed by ameloblasts.

Enamel crystallites are millions of hydroxyapatite crystals in each rod, tightly packed in keyhole shapes, and contribute to the strength of enamel.

Incremental lines in enamel result from amelogenesis and form rings of growth called Stria of Retzius (line of Retzius).

Prismless enamel is unstructured enamel, lacking prisms, found on the surface. It is highly radio-opaque, harder, and less soluble.

The enamel-dentine junction (EDJ) is the functional interface between enamel and dentine and has a scalloped appearance.

Hardest biological tissue that protects underlying tooth layers from damage and bacteria.

Enamel is thickest at cusp tips, occlusal, and incisal surfaces, and withstands pressure from chewing and biting forces.

Enamel is inert tissue (no living cells), formed by ameloblasts during tooth development; cannot regenerate; lacks nerves to feel injury.

Hydroxyapatite crystals capable of ion exchange with saliva. Allowing for uptake/loss of minerals

Enamel includes white, translucent crystallites providing visual appeal and a bright smile.

Dentine is composed of 70% inorganic minerals (calcium hydroxyapatite), 20% organic material (collagen), and 10% water.

Structural features of dentine include dentine tubules, interglobular dentine, sclerotic dentine, dead tracts, lines of Von Ebner, and granular layer of Tomes.

Dentine tubules are small tubes that permeate the dentine structure, extending from the DEJ to the border of the pulp chamber.

Interglobular dentine are unmineralized areas that have failed to fuse at the zones of mineralization during dentinogenesis.

Dead tracts are empty dentine tubules where the odontoblastic process has died or retracted and is sealed off.

Lines of Von Ebner reflect the pattern of dentinogenesis, and Contour Lines of Owen are distinct incremental lines.

Granular layer of Tomes is a narrow layer of dentine with a granular appearance found only in root dentine beneath the CEJ.

Secondary dentine is formed by natural aging process, to help protect the pulp from external stimuli, limits pulp exposure and sensitivity

Tertiary dentine is indicative of pulp reaction to damage or stimuli, associated with caries, restorative procedures, or trauma

Reactionary dentine is produced by existing odontoblasts in response to mild stimuli; it is thinner and more organized.

Reparative dentine is produced by newly differentiated odontoblast-like cells after significant injury and is thicker/irregular

Dentine provides support with its bulk of tooth crown and root, offering rigid yet flexible structure.

Dentine offers protection due to its proximity to pulp and secondary dentine.

Fluid-filled dentine tubules and odontoblastic processes

Tertiary dentine is the repair mechanism to the dentine (odontoblasts deposit tertiary dentine)

Loss of enamel or gingival recession exposes underlying dentine.

The open dentinal tubules providing a pathway for external stimuli to reach to pulp increases sensitivity

In Dentine Hypersensitivity there increased diameter and number of exposed tubules

Fluid that moves in dentinal tubules activates nerve endings leading to hypersensitivity