Evidence for slowly conducting afferent fibres innervating both tooth pulp and periodontal ligament in the cat

Abstract

The presence of afferent nerve fibres branching to innervate both the dental pulp and periodontal ligament was studied in pentobarbitone-anaesthetised cats. Extracellular single nerve-fibre recordings were made from fine filaments split from the proximally cut end of the inferior alveolar nerve. Nerve fibres were identified by bipolar constant-current stimulus pulses applied to the periodontal space via platinum wire electrodes. In each case activation of the nerve fibres was also attempted by monopolar electrical stimulation of the dental pulp via a platinum wire electrode inserted into the dentine. Eleven of 142 C fibres and 4 of 97 A δ fibres identified by electrical stimulation of the periodontal ligament also could be activated by electrical stimulation of the dental pulp. Fourteen of the 142 C fibres identified by electrical stimulation of the periodontal ligament exhibited discrete latency jumps at different suprathreshold stimulus strengths. Eight of them also could be activated by electrical stimulation of the dental pulp. Eight of the 15 fine branching afferent fibres were tested with non-electrical stimuli of both periodontal ligament and dental pulp by application of heat, cold and potassium chloride. Three of the 4 C fibres could be activated with at least one of these stimuli applied to both tissues. In one case receptove fields were located in both periodontal ligament and dental pulp. The remaining 5 slowly conducting fibres were activated only from one type of tissue. The results suggest that a small percentage (6%) of the slowly conducting nerve fibres in the inferior alveolar nerve innervate both the periodontal ligament and the dental pulp. According to their response behaviour they might be involved in nociception.