Electromyographic Assessment of the Masseter and Temporalis Muscles in Skeletal II Malocclusion Subjects With Varying Overjets: A Pilot Study.

Introduction Class II malocclusions are commonly associated with some muscle disharmony and imbalance. Diagnosis of muscle imbalance helps in treating the malocclusion as well as preventing relapse of the treatment. The aim of this study is to compare the muscle activity of masseter and temporalis in patients with skeletal Class II division 1 malocclusion with varying overjet using surface electromyography (sEMG). Materials and methods Ten subjects in the age range 18-35 years with skeletal Class II malocclusion and varying overjets who required orthodontic treatment were included in this study. Out of these 10 patients, five of them had a 2-4mm overjet and the other five had an overjet >4mm. A four-channel sEMG system was used to conduct the sEMG of muscles. Muscle activity, synergy, and symmetry of masseter and temporalis muscles were assessed and compared between the two groups with an Independent t-test. Results There were no significant differences in the muscle activities of the temporalis and masseter muscles in both groups. Symmetry and synergy of these muscles in the two groups also showed no significant difference (p>0.05) at rest and clenching. However, during chewing, the masseter muscle showed poor balance and activity. Conclusion The overjet in Class II division 1 malocclusions did not seem to affect the muscle activity at rest and during clenching. In patients with increased overjet, during chewing, masseter activity in terms of intensity and balance was poor.