1999 Volume 62 Issue 1 Pages 1-11
I investigated the relationship between mandibular closing velocity and masseter muscle (Mm) activity. Eight healthy subjects were instructed to perform two rhythmical opening and closing movements at normal opening and closing velocity (NOC) and maximum opening and closing velocity (MOC). Electromyograms were analyzed during three types of closing (ac-celerating, rapidly decelerating and slowly decelerating) and compared with mandibular kinesiograph vertical motion velocity curves (velocity curves). The distdnce the mandible was opened at maximum closing velocity was divided by the maximum opening distance. This ratio for NOC (58.6%) was similar to that for MOC (48.0%). The time of the decelerating phase at maximum closing velocity was divided by the total time of the closing phase. This ratio for NOC (52.0%) was similar to that for MOC (45.7%). The maximum velocity during the closing phase for MOC was significantly greater than that for NOC. Mm activity during the accelerating phase for MOC was significantly greater than that for NOC. However there was no significant difference between Mm activity during the slowly decelerating phase for NOC and that for MOC. During NOC, Mm activity increased significantly as the closing velocity increased. Paths of the smoothed raw Mm electromyograms were similar to those of the velocity curves, and there was a correlation between the smoothed raw electromyograms of Mm and the velocity curves. A comparatively large amplitude was found in the rectified electromyograms slighty ahead of the wave of velocity curves. These results clearly demonstrate that Mm activity regulates mandibular closing velocity.
