Electrical stimulation of teeth with a pulp tester in the cat.

Responses of 241 pulpal and 219 non-pulpal nerve fibers to monopolar electrical stimulation were studied in 12 anesthetized cats. Stimulation was carried out with a clinically used pulp tester (Bofors PT-l®) to the intact crown of mandibular canine tooth and to the surrounding soft tissues not further than 1.5 cm from the tooth. Action potentials from nerve preparations containing either a single or a few functional fibers were recorded. The minimum current strength needed w excite the axon ("threshold current") was determined. The purpose of the study was to investigate how specifically monopolar electrical stimulation of the tooth crown excites the nerves of the dental pulp and to what extent fibers of surrounding tissue are affected. The mean threshold of excitation of the pulpal nerve fibers was 28.3 μA ± 1.4 s.e.m. Of 219 non-pulpal fibers sensitive to mechanical stimulation of the tooth and the surrounding area, only 10 fibers of periodontal origin were caused to discharge due to electrical stimulation applied to the tooth crown. Their mean threshold was 96.0 μA ± 5.2 s.e.m. When the receptive fields of 50 mechanoreceptor units in soft tissue were stimulated electrically, only nine responded to current values less than 125 μA. It seems that pulp nerve fibers respond to very much lower current intensities than non-pulpal fibers, when monopolar electrical stimulation is applied to the tooth crown. The risk of activation of non-pulpal nerves in pulp tests seems to be minimal supposing that reasonable current strength is used.