Abstract
To evaluate masticatory muscle activity bilaterally during submaximal clenching, an asymmetry index (AI) has been recently introduced by Naeije et al. However the characteristics of AI both in the temporal and masseter muscle activity have not yet been clarified. Therefore in the present study, the influence of clenching efforts and occlusal positions on the AI of the temporal and masseter muscles was investigated.
Forty healthy subjects with normal occlusion (Aged 20 to 37 yrs. old) were asked to clench at 50 percent of the maximum voluntary clenching (MVC) level of the masseter muscles during 5 different clenching tasks as follows: (1) clenching in the intercuspal position (ICP), (2) intentional vertical clenching on the left and right side in the ICP (Int. VR and VL), (3) lateral shift clenching to the left and right side (Lat. R and L). Bite checks were obtained in ICP and Lat. R and L, with green bite wax, and the number of post-canine tooth contacts were calculated bilaterally.
The results were as follows; As to the temporal muscle, the AI of the ipsilateral side changed compared positively with the contralateral side in all of the subjects. However, three patterns were recognized in the masseter muscle AI, by evaluating the predominancy of the ipsi-and contra-lateral side activity at Int. VR and VL, and Lat. R and L. A positive correlation was recognized between the AI value of the masseter muscle and the asymmetry of the number of tooth contacts both in the ICP and Lat. R and L, while it was not found in the temporal muscle.
These results suggested that the AI values were related to the clenching direction and occlusal positions in the temporal muscles, but related to the number of post-canine tooth contacts in the masseter muscles.
