Thresholds of intradental A‐and C‐nerve fibres in the cat to electrical current pulses of different duration

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Abstract
Electrical current pulses of quite variable duration have been used in activation of intradental nerves both in human subjects and experimental animals. It seems, however, that little information is available about the effect of pulse duration on the responses of single pulp nerve units. The aim of the present study was to investigate the effect of pulse duration on excitation thresholds of intradental A‐and C‐fibres in the cat. In 12 anesthetized cats 61 C‐and 53 A‐nerve units were identified and recorded. Electrical thresholds were determined with current pulses of different duration from 0.2 to 50.0 ms. The maximal stimulus intensity was 200 μA.Conduction velocities of all recorded units and absolute refractory periods of 20 A‐and 20 C‐units were determined. Intradental A‐and C‐fibres had different strength‐duration properties. With all pulse durations A‐fibres had the lowest thresholds. Part of the C‐fibres did not respond to the shortest current pulses even with the maximum stimulus intensity (200 μA).With 0.2 ms pulses only 31.1% of the recorded C‐fibres could be activated. In some A‐fibres a single current pulse of long duration was capable of inducing several action potentials, when the stimulus intensity was increased suprathreshold. Refractory periods of A‐units were <2.0 ms and those of C‐units 5.0–9.0 ms. It is concluded that in electrical stimulation of teeth duration of current pulses strongly affects responses of single intradental fibre units. With long pulses function of A‐fibres is pronounced because of repetitive firing in some units. These properties of pulp nerves should also be considered, when electrical stimulation is applied to human teeth.