Excitability changes in trigeminal primary afferent fibres elicited by dental pulp stimulation in the cat

Abstract

The effect of monopolar and bipolar dental pulp stimulation and mechanical facial stimulation on the level of excitability of trigeminal primary afferent fibres was studied. Mechanical facial stimulation resulted in increased excitability of trigeminal primary afferents. Monopolar dental pulp stimulation resulted in a period of increased excitability similar in amplitude and time course to that with mechanical stimulation. This excitability increase was reduced in amplitude, but not abolished, in both cases by dorsolateral medullotomy at the level of the obex. Bipolar dental pulp stimulation resulted in a brief early period of increased excitability of lower amplitude than that seen with monopolar stimulation. This was followed by a prolonged consistent period of decreased excitability. Monopolar dental pulp stimulation also elicited a late period of decreased excitability, but it was inconsistent and of much lower amplitude than that seen with bipolar stimulation. Dorsolateral medullotomy at the level of the obex abolished the excitability decrease seen with both types of dental pulp stimulation. We suggest that monopolar dental pulp stimulation activated large mechanoreceptive periodontal afferent fibres, in addition to pulp fibres, with resultant primary afferent depolarization. Bipolar stimulation apparently activated afferents which were confined almost exclusively to the pulp and resulted in primary afferent hyperpolarization. These results suggest that studies which employ electrical stimulation of dental pulp as a painful stimulus should use exclusively bipolar stimulation, whenever possible. Studies of the sensation or physiologic changes evoked by dental pulp stimulation are difficult to interpret if monopolar stimulation is used. For strictly clinical localization of teeth with pulp pathology, however, the monopolar algesiometers used at present are probably satisfactory.