The method of differential lissajous electromyography (DL-EMG) was applied to investigate the relationship among the integrated EMG activity, timing, and coordination of the bilateral superficial anterior temporal and masseter muscle activities in normal occlusion and Class III malocclusion subjects. In both Class III malocclusion and normal occlusion subjects, the working side muscles showed a higher mean cumulative voltage (MCV) and mean maximum peak voltage (MMPV) compared with the balancing side. In addition, a higher MCV and MMPV of the working side masseter was observed in the normal occlusion group compared with that seen in the Class III group during both right and left side chewing (p<0.01). Discriminant analysis applied to examine the distribution, the size and the shape of DL-EMG pattern further indicated a statistical difference between subject groups (p<0.01). Finally, there was a significantly higher percentage of clockwise DL-EMG pattern-generation in the normal group compared with that seen for Class III subjects (p<0.01). These data indicate that, compared with normal subjects, patients with a Class III malocclusion have a demonstrably abnormal masticatory muscle balance which is well characterized by the DL-EMG method.

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Author notes

Toshio Deguchi is a Professor and Chairman in the Department of Orthodontics, Matsumoto Dental College

Lawrence P. Garetto is an Assistant Professor of Orthodontics and Physiology/Biophysics, Indiana University Schools of Dentistry and Medicine

Youichi Sato is an Instructor in the Department of Orthodontics, Matsumoto Dental College

Rosario H. Potter is a Professor Emeritus of Oral Facial Genetics, Indiana University School of Dentistry

W. Eugene Roberts is Professor and Chairman of the Department of Oral Facial Development, Indiana University School of Dentistry