Functional adaptability of temporomandibular joint mechanoreceptors after an increase in the occlusal vertical dimension in rats

Objective: To investigate the effects of an experimentally-induced increase in the occlusal vertical dimension (iOVD) on the functional characteristics of temporomandibular joint (TMJ) mechanoreceptors in rats. Materials and Methods: Sixty 13-week-old male albino Wistar rats were divided into control and iOVD groups (30 animals each). The vertical dimension between the maxillary and mandibular molars in the iOVD group was increased by 2.0 mm with a build-up of resin on the maxillary molars. Single-unit activities of TMJ mechanoreceptors were evoked by passive jaw movement. Recording was performed from the gasserian ganglion 1 day and 1, 3, 5, 7, and 9 weeks after the establishment of iOVD. Results: Compared with the control group, the firing threshold was significantly lower at 1, 3, and 5 weeks after iOVD in the iOVD group. There were no significant differences in the firing threshold at 1 day, or 7 or 9 weeks. The maximum instantaneous firing frequency was significantly higher at 1, 3, and 5 weeks after iOVD in the iOVD group, but there were no significant differences at 1 day, or 7 or 9 weeks. There were no significant differences in the average firing frequency during the experimental period. Conclusions: The present study findings suggest that TMJ mechanoreceptors in adult rats may ultimately adapt to iOVD. (Angle Orthod. 2011;81:453-459.)