Comparison of electrical thresholds of intradental nerves and jaw‐opening reflex in the cat

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Abstract
In experimental animals the jaw‐opening reflex in response to stimulation of pulp nerves has been used as a nociceptive reflex. However, there seems to be only scanty information about the amount and types of pulp nerve fibres that mediate the reflex. In the present work on 8 anesthetized cats electrical thresholds of single functional pulp nerve units were compared to the thresholds of jaw‐opening reflex. Monopolar cathodal current pulses were applied to each canine tooth. Reflex responses of the digastric muscle were recorded. The inferior alveolar nerve of the left side in 3 cats was exposed for nerve dissection and responses of pulp nerve units coming from the lower left canine tooth were recorded. The mean threshold of the jaw‐opening reflex with 10 ms pulses was 5.9 ± 3.0 (SD) μA.Below or at that level only part of the fast conducting pulp nerve units could be activated. Thresholds of A‐(n=32) and C‐(n=24) fibres were 9.9 ± 5.7 and 37.4 ± 14.5 (SD) μA respectively. Nerves of the periodontal tissues (20 units recorded) were not activated with current pulses of up to 200 μA applied to the tooth. Consequently, at threshold level the jaw‐opening reflex in response to the present type of stimulation is mediated by the fast conducting intradental nerve units.