[Relationship between orofaciocranial morphologic factors and electromyographic activities of the masticatory muscles].

The purpose of this study is to evaluate the relationship between orofaciocranial morphologic and functional factors. The lateral cephalograms of 10 normal subjects were taken and traced. The authors divided cephalometric parameters into linear and angular measurements. Electromyographic (EMG) activities were recorded from bilateral anterior temporal and masseter muscles during tapping movement. Then the total muscle activity of both muscles, and the masseter muscle activity ratio in the total muscle activity were measured. The correlation coefficients between cephalometric measurements and EMG parameters were analyzed. The results of this study are as follows: 1) The total muscle activity revealed positive correlation with all the linear measurements. Especially, the total muscle activity significantly correlated with the size of mandible, such as Co-Go and Go-Me. 2) The total muscle activity showed a tendency to increase when the angles among SN plane, FH plane, maxillary base plane and mandibular border plane became small, and when S-N-A and S-N-B became large. 3) There was no correlation between masseter muscle activity ratio and cranial morphologic measurments. But masseter muscle activity ratio correlated with tooth position and anteroposterior inclination of the anterior teeth. These results suggest that the consideration of the relationship between orofaciocranial morphologic factors and EMG parameters is necessary for examining the masticatory muscle activity.