Muscular Effects of Posterior Crossbite Treatment

Objectives: The aim of this prospective study was to analyze the muscular effect of skeletal crossbite treatment in the mixed dentition. Methods: The sample consisted of 27 children, of both gender, aged from 7 to 10 years, presenting skeletal posterior crossbite and requiring treatment with rapid maxillary expansion. The treatment was performed with the bonded rapid maxillary expansion appliance, used during 4 months after the active phase. After that period, the appliance was removed and patients wore the removable retention for at least 6 months. The electromyographic (EMG) activity of right and left masseter muscles (RM and LM) and right and left temporalis muscles (RT and LT) was analyzed before treatment (T1), four months (T2) and 12 months after treatment (T3). EMG activity was evaluated during habitual chewing (10 sec) using the MyoSystem - Br1 electromyographer. The RMS values of habitual chewing were normalized by RMS of maximum voluntary dental clenching and the data were statically analyzed using the GLM repeated measures analyses. Results: T1: RM=52.19±31.10; LM=59.78±32.12; RT=48.85± 23.56; LT=56.95± 23.76/ T2: RM =95.68±128.54; LM=93.88±94.13; RT= 63.85± 31.97; LT=74.41±43.61/ T3: RM=71.97±46.72; LM=67.78±48.61; RT= 60.74±32.69; LT= 61.15±29.10. Comparing T1 and T2, the EMG activity of RM, LM, RT and LT increased. However, the difference was statistically significant only for RT and LT (p<0,05). At T3, the EMG values were closed from initials ones and there were no statistical differences for any muscles between T1 and T3. Conclusion: Can be concluded that posterior crossbite treatment increased the muscular activity of masticatory muscles in a short-term, however in a long-term the differences were not significant. These findings suggest the association between dental stability and functional adaptation and show the importance of the use of the contention until the muscles have adapted to the new occlusion relationship.