Changes in soft tissue profile and electromyographic activity after activator treatment

Abstract

Abstract Background To date, few studies have correlated the changes in muscle activity and specific soft tissue variables in adolescents with malocclusions. Objective To determine associations between the soft tissue profile and electromyographic activities in temporalis, masseter and orbicularis oris muscles in children with Class II division 1 malocclusions treated with activators. Methods For this prospective study, 25 subjects with Class II division 1 malocclusions were randomly assigned to either a Treatment group (N = 15) or a Control group (N = 10). The mean skeletal ages of the subjects in the Treatment and Control groups were 11.3 ± 1.1 and 11.0 ± 1.3 years, respectively. The subjects in the Treatment group were treated with activators and the subjects in the Control group were untreated. Lateral cephalometric radiographs and EMG recordings of the anterior temporalis and masseter muscles during clenching, chewing and swallowing and the orbicularis oris muscle during whistling were obtained at the start of the study and 12 months later. Changes in the soft tissue profile were correlated with changes in the EMG activities in anterior temporalis, superficial masseter and orbicularis oris muscles. Results The upper lip to E line distance (UL-E) decreased more in the Treatment group than the Control group (p < 0.05) and the H angle decreased in the Treatment group, but increased in the Control group (p < 0.01). The EMG activities of temporalis and masseter muscles increased significantly in both groups. All between-group EMG differences were statistically significant with the exception of the activities in the temporalis and masseter muscles during swallowing. In the Treatment group, a significant positive correlation (r = .57) was found between the changes in UL-E and anterior temporalis activity during swallowing, and significant negative correlations were observed between the EMG activity of masseter muscle during swallowing and changes in LL-E (r = -.54), OLp-UL (r = -.55) and OLp-LL (r = -.67). Conclusions Activator therapy is accompanied by changes in the lips and temporalis and masseter activities during swallowing.