Masticatory muscles coordination index of healthy children and with malocclusion

AIMS: To investigate the masticatory muscles coordination of children with anterior dentoalveolar open bite (OB). METHODS: Fifteen children with dentoalveolar open bite (OB) and no crossbite (7-12 years of age) were evaluated and compared to 15 children without malocclusion (controls, C) (7-11 years). All children were healthy and had Facial Height Ratio (FRH = Jarabak quotient) > 59%. Surface electromyography (sEMG) of the masseter and temporal muscles were recorded during maximum teeth clenching either on cotton rolls between teeth or in intercuspal position (MVC). From the potentials recorded during the MVC tests, standardized by MVC on cotton rolls, the following standardized EMG indices (all in %) were calculated: POC (left and right side percentage overlapping coefficient that assess muscular symmetry), TORS (potential lateral displacing components due to unbalanced contractile activities of contralateral masseter and temporalis muscles), BAR (barycenter, anterior-posterior displacing component). Three more indices linked to the previous ones were computed: mean left-right asymmetry index (Asymmetry), mean momentum (Torque), most prevalent pair of masticatory muscles (Activity). Finally the standardized total activity (Std. IMPACT) was evaluated as the rate between the overall muscular activity performed in MVC and the one with cotton rolls. Descriptive statistics were computed for all variables, which were normally distributed. Mean values were compared by Student’s t tests for independent samples (the significance level was considered for P=0.05). RESULTS: There were no significant differences between children with OB and those with normal occlusion. The observed indices values were respectively: masseter POC [%] (73.0±23.8% vs. 86.1±4.0%), temporal POC [%] (83.9±6.7% vs. 85.8±11.2%), TORS [%] (89.2±5.0% vs. 89.3±7.9%), BAR [%] (81.6±12.3% vs. 84.6±15.5%); Asymmetry [%] (13.8±15.3% vs. 7.3±11.0%), Torque [%] (7.0±6.7% vs. 6.2±9.4%), Activity [%] (15.5±14.5% vs. 11.4±17.5%); Std. IMPACT [%] (121±5% vs. 148±5%). CONCLUSION: OB children had all mean indices worse than control children, but no significant differences were found because of the large inter-subject variability; an aspect that should be deepened in future studies. ACKNOWLEDGEMENT: The first author received a fellowship from: The State of São Paulo Research Foundation (FAPESP) –Brazil. This work was supported by Provost’s Office for Research of the University of São Paulo.