Conduction velocities of single pulp nerve fibre units in the cat.

Abstract

Most experiments on dental nerves have been made using dentine recording technique and it seems that only the fast conducting myelinated pulpal nerve fibres can be recorded with this technique. However, histological studies have revealed that even 80% of intradental fibres in the cat are unmyelinated. In the present work we studied activation of intradental nerve fibres with monopolar electrical stimulation of the intact mandibular canine tooth crown of the cat. The purpose was to determine the proportion of responding intradental A‐and C‐fibres dissected from the inferior alveolar nerve. In 17 anesthetized cats 350 pulp nerve fibre units were identified and recorded. Conduction time (based on the shortest latency), distance between the stimulation and the recording sites and threshold current for each fibre unit were determined. The mean conduction velocity for all pulp nerve fibres was 9.2 m/s (SD=9.8). The number of C‐fibres (conduction velocity ≤2.0 m/s) was 122 (34.9%) and the number of A‐fibres was 228 (65.1 %). The mean conduction velocities of C‐ and A‐fibres were 1.0 m/s (SD=0.4) and 13.4 m/s (SD=9.4), repectively. The mean threshold current was 22.8 μA (SD=20.1) for the whole group, 40.4 μA (SD=20.7) for C‐fibres and 13.5 μA (SD=11.8) for A‐fibres. Although the function of pulpal C‐fibres is poorly known, it has been suggested that they have a distinct role in mediation of sensations from tooth, particularly in inflammatory processes. Using nerve dissection technique the activity of a considerable part of intradental C‐fibres can be recorded and it seems to be the only available method to study the function of this fibre group.