Etiology of dentin hypersensitivity.

Hypersensitive dentin appears to be mainly the result of an activation of the dentinal pain fibres, the A-fibres, at the pulpal wall. The stimuli which activate these nerves are primarily those which remove fluid from the dentinal tubules and mobilize capillary forces, causing a rapid outward flow. Application of a cold stimulus causes the fluid to contract, resulting in a similar rapid outward flow in the pulpal region of the tubules. Hypersensitivity to cold is also marked when there is a fluid-filled gap containing bacteria in the tooth. Experiments have shown that a freshly exposed dentin surface with patent tubules is more sensitive than a surface contaminated by a smear layer. Inflammation in the adjacent pulpal region can also increase sensitivity. The development of hypersensitive cervical and occlusal surfaces is due to mechanical and acidic effects from the oral environment, toothbrush abrasion, erosive components in the diet, plaque and bacterial invasion of dentin. Sometimes dentin is exposed by restorative therapy and occasionally eccentric occlusal loads can contribute to hypersensitivity. The sensitivity may persist unless the open tubular apertures are sealed.