Electromyographic and ultrasonographic observations of masseter and anterior temporalis muscles in children.

Muscle thickness and activity of masseter and anterior temporalis muscles in children with Class I molar occlusion having normal anterior relation, anterior deep-bite and anterior open-bite were measured using ultrasonographic and electromyographic techniques. The results demonstrated an increased muscle thickness in the deep-bite followed by open-bite subjects. Muscle activity was high in the same groups. A significant correlation between thickness and activity was noted only in the anterior temporalis muscle of subjects with normal anterior relation. Activity index indicated that masseter contributed to the higher activity in the clenching effort.