Electromyographic Evaluations of Masticatory Muscle Activity between Patients with Skeletal Class I and III Relationships

Objective The aim of this study was to compare the muscle activity of the masseter muscle (MM) and anterior temporal muscle (TA) of patients with skeletal Class I and III during maximum voluntary clenching (MVC) at the intercuspal position (ICP) and during chewing. Materials and Methods Twenty patients were divided into Steiner's skeletal Class I and III groups. MM and TA activity during each task was measured by using surface electromyography. Averaged MM and TA activity during both tasks, symmetry of each muscle activity, synergy between ipsilateral MMs and TAs, and muscle effort were compared. Statistical Analysis Means and standard deviations of intergroup variables were compared by an independent sample t -test for parametric evaluations or by the Mann–Whitney U test for nonparametric evaluations. A probability value of p less than 0.05 was considered significant. Results Averaged MM activity and muscle synergy during MVC at the ICP in skeletal Class III patients were lower than that in skeletal Class I patients. Neither symmetry nor muscle effort during both tasks was different. Conclusion Masticatory muscle performance of skeletal Class III patients was inferior to that of skeletal Class I patients.