Circadian changes in stimulus threshold and in the effect of a local anaesthetic drug in human teeth: studies with an electronic pulptester.

An electronic pulptester with constant testing current was used to study the stimulus threshold in human teeth of 28 healthy volunteers and the duration of local anaesthesia by articaine plus epinephrine in 55 patients with caries who underwent a filling therapy. In 21 out of the 28 volunteers, significant daily variations in stimulus threshold were detected by cosinor analysis. Acrophases, however, were scattered over the 24-hr scale. In patients, the local anaesthetic effect was studied at four different times of day (0800, 1100, 1400 and 1700 hr). The electronic device allowed one to accurately determine the time to peak effect (Tmax), duration of effect (Emax, time to return to baseline threshold (Tret) and the area under the time-effect curve (AUC) as a measure of the total local anaesthetic effect. Significant diurnal variations in AUC and Emax were found in 36 patients with the 0.8 ml dose, with peak and trough values at 1400 and 1700 hr, respectively. No differences in effect were found with the low dose of 0.4 ml applied to 19 patients either at 1400 or 1700 hr giving evidence for a circadian phase-dependency in the dose-response relationship of a local anaesthetic drug. The results clearly demonstrate that this electronic device is suitable for exact evaluation of circadian changes in local anaesthetic effects. Under drug-free control conditions, however, the low stimulus frequency of 5 Hz of this device obviously does not allow to discriminate between stimuli modified by pain perception and/or alertness.