Effects of Thickness and Hardness of Mouthguard on Soleus H-reflex

Objectives:We often see the sports athletes who wear mouthguard for the purpose of protection their teeth from injury. In general we can enhance the athletic performance with voluntary clenching of the teeth, but it is not fully understood how voluntary clenching with mouthguard influence on motor activity. To investigate the effects of thickness and hardness of mouthguard on motor activity, we recorded soleus H-reflex for evaluation of motor activity, and examined the relationship between thickness and hardness of mouthguard and the modulation of soleus H-reflex.Methods:The subjects were 7 males (aged 18 to 35) with normal dentition. The soleus H-reflex was evoked by stimulating the tibial nerve on the popliteal fossa of each subject. First we examined the stimulation threshold displaying the maximum amplitude of the H-wave in each subject, and performed the following experiments; 1) the recording of the H-reflex with clenching without mouthguard, 2) the recording of the H-reflex with clenching of four different types of mouthguard made of soft and hard material with thickness of 2 and 4 mm. Friedman test with Bonferroni correction for multiple comparisons) was used to study comparison among groups. P values <0.05 were considered significant.Results:The amplitude of H-wave induced by clenching with or without insertion of mouthguard was larger than the amplitude of H-wave at resting jaw position (p<0.05). The amplitude of H-wave induced during clenching with soft mouthguard of 2 millimeters thick was larger than that with any other types of moutguard (p<0.05).Conclusions:These results suggest that the voluntary clenching is important for stabilization of motor activity and the types of mouthguard have an influence on physical performance.