BACKGROUND/OBJECTIVES: Long-term neuromuscular effects of rapid maxillary expansion (RME) for functional posterior crossbite (FPCB) remain unclear. This prospective longitudinal study evaluated RME effects on masticatory muscle electromyographic (EMG) activity and transverse skeletal/dental dimensions in children with FPCB. MATERIALS/METHODS: Seventeen FPCB patients (mean age 8.8 years) treated with Hyrax expanders and 15 age-matched controls with normal occlusion were evaluated. Surface EMG activity, dental casts, and posteroanterior cephalograms were recorded at baseline (T1) and at the final evaluation (T2), with a mean interval of 10.6 months between assessments, encompassing the active expansion phase followed by 6 months of removable retention. RESULTS: EMG analysis showed significantly increased masseter and temporalis activity after RME, indicating improved neuromuscular function. Cephalometric measurements revealed significant increases in maxillary skeletal width and maxillo-mandibular skeletal ratio without mandibular changes. Skeletal expansion (2.97 mm) represented 51% of the total maxillary intermolar width increase (5.86 mm), demonstrating favorable skeletal contribution. The maxillary-to-mandibular intermolar ratio normalized compared with controls. LIMITATIONS: Small sample size, single-center design, and 10-month follow-up duration may limit generalizability and long-term stability assessment. CONCLUSIONS/IMPLICATIONS: RME significantly improves maxillary transverse dimensions and masticatory muscle activity in young FPCB patients. Early treatment optimizes skeletal-to-dental expansion ratio and promotes favorable stomatognathic system development.
Gameiro et al. (Thu,) studied this question.