Response properties of periodontal mechanoreceptors in rats, in vitro.

Single unit activities of the inferior alveolar nerve evoked by calibrated von Frey stimuli (1.1, 2.9, 7.8, 11.8, and 17.2mN) on the periodontal ligaments of the mandibular molars or incisors were recorded in an in vitro jaw-nerve preparation of Wistar albino rats. The data of 55 (lower incisor) and 100 (lower molars) units were collected in the present study. Both rapidly (RA) and slowly adapting (SA) type units were found in the incisors, and most of these units were innervated by Abeta fibers. While all the units of the molars were of RA types, the innervated fibers of two-thirds (67/100) of the units have been identified as Adelta fibers. The response patterns of the RA type were subdivided into three types (ON, OFF or ON-OFF type) both in the incisors and the molars. While von Frey thresholds of all incisor units were 11.8 mN except one unit that was 7.8 mN, those of the molars varied from 2.9 to 11.8 mN. In the molars, a majority of afferents innervated the periodontal ligaments of more than one tooth. This study suggests that response properties of periodontal mechanoreceptors are different between the incisors and the molars in rats, suggesting that these receptors have different functions in the regulation of mastication.