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Portrait of Dentine

Anatomy · Head, neck & teeth

Dentine

The bulk of the tooth, beneath the enamel

Tooth · the layer around the pulp

The yellowish calcified tissue that forms the bulk of a tooth, lying beneath the enamel of the crown and the cementum of the root and surrounding the pulp cavity. It is harder than bone but softer than enamel and is traversed by microscopic tubules containing the processes of odontoblasts. Unlike enamel it is living tissue, laid down throughout life and sensitive when exposed.

How to spot them

  • ▸The yellowish layer between the hard white enamel and the soft pulp
  • ▸Roughly 70 per cent mineral, 20 per cent organic (chiefly collagen) and 10 per cent water
  • ▸Perforated by tiny tubules running from pulp to the outside of the layer
  • ▸Formed by odontoblasts lining the pulp cavity, which go on laying it down for life

What to know

Roughly 70 per cent mineral, harder than bone but softer than the layer above it in the crown

Dentine, the main calcified tissue of the tooth

Riddled with tens of thousands of microscopic channels per square millimetre, each holding the process of a cell named after Tomes

Dentinal tubules containing odontoblast processes (Tomes' fibres)

Brushing with cold water or eating ice cream hurts when the covering wears away and exposes these channels, because fluid movement stimulates the nerves

Dentine hypersensitivity — the hydrodynamic theory of pain

Laid down as a pale band at the boundary with the pulp throughout life, gradually shrinking the pulp chamber

Secondary dentine, formed by odontoblasts after the tooth erupts

The substance of an elephant's tusk, which is what we call ivory

Ivory is dentine — the tusk is an enlarged incisor

A reactive layer formed in response to decay or wear, blocking the path to the pulp

Tertiary (reparative) dentine

Derived from neural crest mesenchyme, and forming a cushion that absorbs the load that would otherwise crack the brittle covering

Dentine, laid down by odontoblasts from the dental papilla

Key ideas

  • Dentine is the resilient core of the tooth. Its collagen makes it tougher than enamel and lets it absorb the shocks that would fracture the brittle enamel cap.
  • The tubules explain why teeth hurt: they contain fluid, and changes in temperature or osmotic pressure move it, stimulating nerve endings at the edge of the pulp.

Quick-fire facts

  • •About 70 per cent inorganic (hydroxyapatite), 20 per cent organic (mostly type I collagen) and 10 per cent water by weight
  • •Tubule diameter is about 2.5 micrometres near the pulp and 0.9 micrometres near the enamel; there are roughly 45,000–65,000 per square millimetre near the pulp
  • •Primary dentine forms until the root is complete; secondary dentine is laid down throughout life; tertiary dentine forms in response to injury
  • •Odontoblasts sit at the edge of the pulp and send processes into the tubules (Tomes' fibres, after John Tomes, the English dental pioneer)
  • •Dentinogenesis imperfecta is an inherited disorder producing weak, opalescent blue-grey or brown teeth, sometimes together with osteogenesis imperfecta
  • •Dentine is covered by enamel over the crown and by cementum over the root
  • •The pulp, in the centre of the dentine, contains the nerves and blood vessels of the tooth
  • •Yellow dentine shines through translucent enamel, so teeth look darker or more yellow as enamel thins with age

Drill it — 7 cards

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Sources