Dentin

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Structure and surrounding structures of a tooth seen in cross section.

Dentin is the calcified connective tissue which forms the bulk of the tooth, providing it with its basic shape and rigidity. It is tougher than bone, and has a higher hydroxyapatite content, which constitutes about 70% of its dry weight. Also, unlike bone, dentin is avascular, does not remodel and is deposited incrementally. Dentin of the crown of the tooth is covered by enamel, whilst dentin in the root is covered by cementum. Deep to it is an enclosed space called the pulp cavity.

A striking feature of dentin are the dentin tubules, which are microscopic parallel-oriented tubules that radiate throughout the dentin from the pulp cavity to the enamel. These tubules contain fluid and the processes of the dentin producing cells, odontoblasts. If the enamel covering the dentin is eroded away and the dentin tubules are exposed, the fluid within the tubules moves. This in turn activates pain receptors at the periphery of the dental pulp. This is thought to be the mechanism of pain sensation in teeth, which can be triggered by various stimuli such as temperature, touch or chemicals.