OBJECTIVE: The purpose of this study was to compare, electromyographically, the action potential of the orbicularis oris muscle, upper and lower segment, bilaterally, in youngsters with Class II division 1 malocclusion and youngsters with normal occlusion, in order to verify the occurrence or not of the different electromyographic activity for both groups. METHODS: The sample consisted of 50 females, ranging from 8 to 10 years old, with no previous orthodontic treatment, divided into two groups: 25 with Class II division 1 malocclusion and 25 with normal occlusion. The electromyographic signals of the orbicularis oris muscle were acquired by Ag/AgCl surface electrodes. Muscle activity was recorded in resting position, in isometric contraction and in isotonic contraction, determining the RMS values of each movement. The data collected was submitted to the statistical analyses of variance and Tukey test (α=0.05). RESULTS: The results showed that there was electromyographic activity difference between the young females with Class II division 1 malocclusion and the ones with normal occlusion. That muscle activity was higher in young females with malocclusion than in young females with normal occlusion. CONCLUSION: This suggest the smaller competence of the orbicularis oris muscle in the females with Class II, division 1 malocclusion.
Electromyography; Orthodontics; Class II, division 1; Normal occlusion; Orbicularis oris muscle
