Effects of mouth guard wearing on dynamic visual acuity

Abstract

To determine whether mouth guard (MG) wearing improves performance capacity of athletes, we examined the effects of MG wearing on dynamic visual acuity (DVA). Subjects were asked to read and answer 3 numerals presented sequentially at random order. The numerals moved left to right at 90 deg/sec on a CRT monitor under two conditions of head motion: 1) stationary state, and 2) voluntary rightward rotation. In each condition, thirty trials with and without MG were carried out and numbers of correct answers (full score; 3 x 30 = 90) were evaluated as DVA score. We measured DVA improvement indexes (= DVA scores with MG minus those without MG) and occlusal forces. In the condition 1, the correlation-coefficient between DVA improvement indexes and occlusal forces was negative (r=-0.74) for nine subjects (20-32 years), whose DVA improvement indexes were >0 in the condition 2. On the contrary, the correlation-coefficient was positive (r=0.76) in the condition 2. These results suggested that the effects of MG wearing on DVA strongly depended on the condition of head motion and the occlusal force. As we recorded simultaneously electromyographic activities of masseter and sternocleidmastoideus, eye movements and head angular velocities, these data will be described to discuss the effects of MG wearing on DVA. [J Physiol Sci. 2006;56 Suppl:S177]