Influence on isometric muscle contraction during shoulder abduction by changing occlusal situation.

Many studies have been performed on the mandibular orthopedic repositioning appliance (MORA) as an athletic performance enhancer since the late 1970s. The concept that changing the mandibular position would increase the strength and improve the performance of subjects has been a source of controversy among various researchers. The strength of shoulder abduction and electronic activities of six muscle groups in the upper body were tested on seven subjects in this study. The normalized data for four different situations: rest position, MVC (Maximum Voluntary Contraction) in an intercuspal position, MVC with placebo, and MVC with MORA in supported rest position were analysed. Statistical analysis demonstrated that the MVC with MORA was significantly stronger than the rest position for upper appendage strength. The electronic activities of all muscle groups were significantly greater with MORA than those in rest position, and some of them were significantly greater with MORA than with either MVC or placebo situation. THe results suggested that the muscle activities of the upper appendage were increased by biting MORA in the supported rest position during the shoulder abduction performance.