[Response properties of the jaw-closing muscle spindle during decreased occlusal vertical dimension in rats].

The masseter-muscle spindle is regarded as being highly adaptable to increases in the occlusal vertical dimension (iOVD), it is hypothesized that spindle function would adapt to a decrease in occlusal vertical dimension (dOVD) as well. Seventy-five 5-week-old female Wistar rats were divided into Control (n = 25) and Experimental (n = 50) groups; those in the Experimental group received a 2.0-mm composite resin build-up to the maxillary molars. The Experimental group was divided into the resin-removal group (n = 25, build-up resin was removed) and the non resin-removal group (n = 25) 8 weeks later; i. e., when the animals were 13 weeks old. Electrophysiological recordings were obtained from masseter-muscle spindle afferents in 13, 14, 15, 19, 21-week-old rats (n = 5 rats each) under general anesthesia Masseter-muscle spindle sensitivity was significantly lower in the resin-removal group 1 week after resin-removal and for the rest of the observation period. The present results indicate that masseter-muscle spindles may not completely adapt to dOVD and may affect jaw function.