[Response properties of rat periodontal mechanoreceptors in an in vitro preparation].

Responses of periodontal primary afferents to mechanical stimulation were investigated in an in vitro jaw-nerve preparation from Wistar albino rats. Single unit activities of the inferior alveolar nerve evoked by von Frey stimuli were recorded using the microneurographical technique. Fifty-five (lower incisor) and 100 (lower 3 molars), units responding to spikes of the mechanical stimulation of the periodontal ligament left attached to the alveolar bone surface after extraction, were obtained. Both rapidly adapting (RA) type and slowly adapting (SA) type receptors were found among fibers in the incisor, while only RA type was found in the molar. The majority of these receptors were innervated by A delta fiber. The threshold in the incisor unit was 11.8 mN except for one (7.8 mN), while those innervating the molar showed various values (11.8, 7.8, and 2.9 mN). The response patterns of the RA type were divided into 3 types (on, off, and on-off type). In the molar, almost all of single primary afferents innervated the periodontal ligaments of more than one tooth, and in on-off type units innervating the molar periodontal ligament, a significant difference of mechanical threshold was found among the three groups classified by the number of the innervating periodontal ligaments.