Anatomy
Dentin
Dentin is the layer of a tooth that sits under the enamel and cementum. It makes up most of the tooth and contains tiny tubes that lead toward the nerve.
Dentin is the hard tissue that forms the bulk of a tooth. It lies under the enamel on the crown and under the cementum on the root. Dentin is softer than enamel. It also contains microscopic tubes, called tubules, that lead toward the tooth pulp.
When enamel wears away or gums pull back, the tubes in dentin are exposed. Heat, cold, sweets or acids can then reach the nerve and cause a short, sharp twinge. This is a common cause of tooth sensitivity.
Dentin can also decay once a cavity reaches it. A dentist can check for decay at an exam and talk with you about next steps.