Influence of Occlusal Hypofunction Induced by Opposed Tooth Loss on Periodontal Mechanoreceptors in Rat Molars

Abstract

It has been critical in clinical dentistry to understand the response properties of periodontal mechanoreceptors (PMRs) when the occlusal condition was changed, because the PMRs are important sensory receptors controlling jaw movement. Therefore, we investigated the effect of opposed tooth loss on the response properties of PMRs in rat molars. All mandibular molars in an in vitro jaw-nerve preparation, made from a rat without opposed teeth, were carefully extracted before electrophysiological recordings. Single-unit discharges evoked by direct mechanical stimuli with von Frey hairs applied to the PMRs were recorded from the inferior alveolar nerve on day 3, and 1, 2, 4, 8, and 12 weeks after opposed tooth extraction. The following results were obtained; (1) in both the 3-day and 1-week post-extraction groups, the von Frey threshold value was significantly lower, although in the 12-week group, it was significantly higher than that in the control group and (2) in the 3-day to 8-week groups, the conduction velocity of nerve fibers innervating PMRs was significantly slower than that in the control group. These results showed that sustained functional changes could be clearly elicited in PMRs by occlusal hypofunction, suggesting that these changes may have critical influences on both jaw reflexes and masticatory movements.