The purpose of this study was to assess by surface electromyography (sEMG) the changes in upper and lower orbicular oris (OO) muscles produced by a preformed functional device in subjects with Class II, division 1 malocclusion, deep bite, and labial incompetence. Twenty-eight subjects were selected: 13 subjects (mean age 9 ± 1.5 years) with Class II malocclusion, deep bite, and labial incompetence were treated with a preformed functional device, while 15 subjects (mean age 9.5 ± 0.8 years) with normal occlusion were used as control. Inclusion criteria for both groups were: presence of mixed dentition, no previous orthodontic treatment, and absence of speech disturbance. sEMG recordings were taken at the time of the first visit (T0), and after 3 (T1) and 6 months (T2) for the treated group, and at T0 and T2 for the control group. The sEMG recording was performed at rest, and while kissing, swallowing, opening the mouth, clenching the teeth, and during protrusion of the mandible, by placing electrodes at the area of muscle contraction. At T0, except during swallowing, the treated group always showed a lower sEMG activity of the lower OO muscle with respect to the control group, with significant differences at rest and during mandibular protrusion (p<0.05). In the treated group, a significant increase in muscle tone was observed for the lower OO muscle from T0 to T1, but only at rest. The upper OO muscle showed a significant increase during the protrusion of the mandible from T1 to T2. No significant change was observed in the control group during the follow-up. Muscular contractility of treated patients at T2 reached the same values as that of the control group at T2. Interceptive orthodontics seems to improve the form and function of the orofacial muscle structure. Improvement in muscle contraction after treatment was demonstrated by sEMG.
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