Responses of intradental nerves to electrical and thermal stimulation of teeth in dogs.

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Abstract
Experiments were carried out to investigate the mechanism whereby thermal stimuli excite nerves to produce pain from teeth. Recordings were made from single fibers dissected from the inferior dental nerve in dogs during thermal stimulation of the lower canine tooth. In preliminary experiments, no units were found with thresholds close to the thresholds for pain in man (45 and 27.degree. C) and subsequently, test stimuli of 55.degree. C, applied for up to 15 s, and 0-5.degree. C were used. Of 117 fibers tested, 43 responded to cooling but not to heating and 9 responded to heating but not to cooling. By applying thermal stimuli directly to the saphenous nerve in cats, it was shown that these responses might have been due to direct excitation of nerves and not to stimulation of specialized receptors. Some units responded to electrical stimulation of the tooth pulp with a latency which decreased abruptly at a critical intensity as the stimulus was increased above threshold. This was possibly due to branching of the fibers.