[On circadian variations of the placebo effect on the pain threshold of healthy teeth: Contribution to a physiology of placebo effects (author's transl)].

Placebo doses can influence the pain threshold of healthy teeth according to the label. Systematic longitudinal researches over the day with measuring the utilization time of cold stimulus on healthy front teeth demonstrate that the placebo effect is subject to significant circadian variations. During daytime a pseudo-analgesic causes a stronger and steeper onset of increase of the tooth pain threshold than during the night, when the pain threshold is influenced only minimal or even inverse. The placebo effect can come up to 40% of the pain threshold increase caused by a usual analgesic; this portion, however, is as well subject to high circadian variations. The extent of the placebo effect corresponds to the order of magnitude of the spontaneous circadian variations of pain threshold and correlates positively to it. These correlations are considered as indicating that those vegetative mechanisms causing the circadian variations of the pain threshold are equally involved in affecting the placebo actions.