Malocclusion and masticatory muscle activity: a comparison of four types of malocclusion.

Electromyographic activities of the temporalis and masseter muscles during mastication were measured in patients who visited this clinic for orthodontic treatment of progenia. The results obtained were compared with those previously obtained in patients with other types of malocclusion and relationships between types of malocclusion and activities of the masticatory muscles were examined. Several interesting results were obtained, including: 1) the muscle activities were significantly higher in patients with deep bite than in patients with any other types of malocclusion and 2) inefficient mastication patterns, evidenced by higher temporalis muscle activities on the balancing side than on the working side, were most frequently observed in patients with edge bite. These results indicate that the clinical evaluation of masticatory muscle activities may be useful in improving orthodontic treatment and in determining a proper retention period after the treatment. The results also suggest that orthodontic treatment should include some type of dynamic myofunctional therapy in addition to the correction of static structural abnormalities.