Changes in Orbicularis Oris Superior and Masseter Muscle Activities After Upper Incisor Protrusion in Class II Division 2 Malocclusion: An Electromyographic Study.

Objective: This prospective study aimed to evaluate the orbicularis oris superior and masseter muscle activity changes after upper incisor protrusion in CII/2 malocclusion.

Methods: A total of 20 patients (mean age 10.29 ± 0.90 years) with CII/2 malocclusion were selected for the study group. A total of 15 patients (mean age 10.56 ± 1.06 years) with Angle Class I malocclusion were recruited as control. Upper incisors were protruded with utility arch in the study group. Muscle activities were evaluated with Biopac MP150 surface electromyography device before and after upper incisor proclination and at the 6-month retention. Orbicularis oris superior and left-right masseter muscles were recorded during rest electromyography and maximum contraction electromyography. Repeated measures and two-way repeated-measures analysis of variance with Bonferroni correction were used for statistical analysis.

Results: A significant change occurred over time in orbicularis oris superior (P < 0.001), left masseter (P < 0.01) and right masseter (P < 0.05) maximum contraction electromyography in the CII/2 group. However, a significant difference was not found between groups P > 0.05. In the CII/2 group, orbicularis oris superior maximum contraction electromyography value was increased after upper incisor protrusion and this increase remained stable. Left masseter and right masseter maximum contraction electromyography measurements were decreased after protrusion and then increased after retention significantly. Rest electromyography values for all muscles were not statistically significant. No significant differences with the control group were found.

Conclusion: Upper incisor protrusion increased orbicularis oris superior activity and the increase remained stable after retention. Masseter activities decreased after protrusion and then increased to the initial values. These changes did not show significant differences with the control group.