[Response properties of pulpal nerve fibers with different conduction velocities]

Tapering and branching of the nerve fibers cause the conduction velocity (CV) along the axon to be unequal. The purpose of this study was to investigate the response properties of the myelinated and unmyelinated nerve fibers in the cat tooth pulp. Electrophysiological recordings were made from the functional single fibers innervating the lower canine tooth pulp in 25 adult cats anesthetized with pentobarbital sodium after the application of four types of stimuli to the canine tooth. A total of 272 single pulpal nerve fibers was identified. A-fibers (n = 215) were divided into two groups: One (Ac, n = 55) consisting of the fibers whose intrapulpal CVs were less than 2 m/s and the extra-pulpal CVs of more than 2 m/s, and the other (At, n = 160) consisting of the fibers whose CVs were more than 2m/s both inside and outside the tooth pulp. Fifty-seven C-fibers (C) were also found. None of C, 47% of At and 46% of Ac responded to the rapid elevation of the temperature. None of At, 38% of Ac and 53% of C responded to the continuous heat. None of C, 20% of At and 20% of Ac responded to the hydrostatic pressure. None of At, 86% of Ac and all of C responded to bradykinin. These results suggest that the functional difference between the pulpal A-and C-fibers is not clear and that the Ac-fibers may complicate the dental and pulpal pain.