The neurophysiology of the teeth.

Irritation of human teeth can evoke pain sensations of varying qualities depending on the type and intensity of the stimuli used. For example, drilling or air drying of dentin typically induces sharp, piercing pain, while intense heating of the tooth can cause dull, aching pain sensation. The dental pulp is richly innervated by both myelinated (A-fibers, mostly A delta-type) and unmyelinated (C-fibers) axons. A-fibers seem to be responsible for the sensitivity of dentin. They respond to stimuli that induce sharp pain in human teeth, for example, drilling of dentin and drying of dentin with air blasts. C-fibers are activated only when the stimuli used reach the pulp proper. They respond to intense heating. In human teeth, dull pain is induced at a temperature level corresponding to the heat thresholds of intradental C-fibers. The other functional characteristics of C-fibers indicate that they may play a role in the mediation of the dull pain connected with pulpal inflammation. Accordingly, activation of intradental nerve fibers of A- and C-type may contribute to the varying qualities of pain sensations induced by stimulation of human teeth.