What Is Dentin (Dentine)? The Layer Under Your Enamel

A tooth is built in layers. On the outside of the crown is enamel. Under the enamel is dentin, which forms the bulk of the crown and also the root, where cementum covers it instead. At the centre is the pulp, the soft core with nerves and blood vessels. Dentin therefore sits between the hard shell and the nerve.

It is yellowish and slightly flexible, which helps cushion the brittle enamel above it. It is also why a tooth looks more yellow as enamel thins with age: the dentin shows through. Both spellings are correct; dentin is the American form and dentine the British one.

Dentin is crossed by thousands of microscopic channels called tubules, running from the outer surface toward the pulp. They hold fluid. When dentin is exposed, a change at the surface such as cold air, a sweet drink or a toothbrush moves that fluid, and the nerve at the other end picks up the movement as a short, sharp pain.

This is the usual cause of sensitive teeth. It happens when enamel wears thin, or when the gum recedes and uncovers the root, where there is no enamel to begin with. Our page on sensitive teeth covers the causes and what a dentist can do.

Once decay passes through the enamel it reaches dentin, and it spreads faster there because dentin is softer. This is why a cavity that feels small on the surface can be wide underneath, and why a filling is needed before it nears the nerve. Our guide on cavities in teeth shows how decay progresses.

The tooth does try to defend itself. The pulp can lay down extra dentin on the inside wall in response to wear or decay, which thickens the barrier between the nerve and the outside. This protective response is limited, so it does not replace treatment.

The aim is to stop dentin being exposed, or to block the tubules where it is. Brush gently with a soft brush, avoid frequent acid drinks, and see a dentist for gum recession or grinding. Toothpastes made for sensitive teeth, which contain ingredients such as potassium nitrate or stannous fluoride, can reduce the response when used regularly.

Sensitivity that is brief and triggered by cold is usually exposed dentin. Pain that lingers, wakes you at night or comes with swelling points to a deeper problem and needs a dentist. For an overview of all the layers, see our guide to the types of teeth.