Effects of variations in rectangular pulse duty cycle and intensity on pulsating direct current electro-analgesia of cat tooth pulp

Abstract

Action potentials in single pulp-driven units of the trigeminal ganglion were elicited by bipolar electrical stimulation of the maxillary canine tooth pulp in cats anaesthetized with a barbiturate. The effects of electro-analgesia currents ranging in peak values from 10 to 100 μA applied to the test tooth were investigated independently for three pulsating direct-current waveforms comprised of trains of monopolar anodal rectangular pulses of various duty cycles. The effects of constant direct-current analgesia were used as a standard for comparison. Logarithmically-spaced duty cycles (per cent on time) of 1.00, 3.16 and 10.0 per cent were investigated, using a fixed frequency of 1000 Hz. Intensity-dependent pulp threshold elevations reaching approximately 400–500 per cent were observed for both constant direct current and 10 per cent duty cycle pulsating direct current analgesia of 20–70μA. In contrast, pulsating direct current analgesia waveforms having duty cycles of 3.16 and 1.00 per cent were approximately 25 per cent effective and ineffective, respectively, when compared to continuous direct current analgesia. The maximum effect was attained with waveforms of 70 μA. Averaged pulp thresholds dropped to near normal values within a few minutes following the termination of effective electro-analgesia. The results indicate that pulsating direct-current analgesia composed of rectangular anodal pulses of 10 per cent duty cycle and 1000 Hz frequency produces effects indistinguishable from that of continuous direct current analgesia at comparable peak intensities.