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Introduction. There is evidence that patients with posterior crossbite (PXB) have neuromuscular changes in the masticatory muscles. However, up to the present time, the relationship among these changes on the electromyographic activity of the masticatory muscles is still unclear. Objective. To systematic review the available literature on the electromyographic activity of masticatory muscles in adults with PXB. Methods. Between August 22 and September 9, 2020, we searched the following seven electronic databases: PubMed, EMBASE, Web of Science, Cochrane Library, SciELO, LILACS, and Scopus. No restrictions were applied regarding the language and year of publication. This systematic review was registered in the Prospective Register of Systematic Reviews (PROSPERO - CRD42020205057) database and conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. After data selection and extraction, the methodological quality of the selected studies was conducted independently by two reviewers, using two different evaluation tools. Results. 6957 records were initially located after the search process. In the end, eight papers were selected. Most studies were classified as having average to low methodological quality and moderate to high risk of bias. Based on the available evidence, adult patients with PXB have electromyographic activity changes in the masticatory muscles when compared with individuals without PXB. Moreover, adult patients with unilateral posterior crossbite (UPXB) have asymmetrical electromyographic activity when the crossbite side is compared with the noncrossbite side. Conclusion. Despite the lack of studies with high methodological quality, electromyographic evaluation of masticatory muscles should be considered in the diagnosis and in the orthodontic treatment plan of patients with PXB. Prospective studies with a higher sample size and follow-up time, conducted using a rigorous scientific methodology, are necessary to reach a more reliable conclusion.

RESUMO Objetivo: Revisar a literatura sobre eletromiografia dos músculos da mastigação em indivíduos com mordida cruzada posterior (MCP). Metodologia: Busca na base de dados Pubmed, utilizando os descritores "posterior crossbite" e "electromyography". A busca foi limitada a periódicos revisados por pares e compreendeu apenas artigos publicados nos últimos 10 anos em língua inglesa. Resultados: Quatorze artigos científicos sobre eletromiografia dos músculos da mastigação e MCP foram incluídos neste estudo. A atividade eletromiográfica nos músculos da mastigação em indivíduos com MCP é amplamente investigada. No entanto, resultados controversos foram encontrados em relação à atividade muscular. A divergência dos resultados encontrados é atribuída ao tamanho e à idade da amostra, assim como à metodologia empregada na avaliação eletromiográfica. Conclusão: A mordida cruzada posterior está associada às alterações na atividade nos músculos temporal anterior (TA) e masseter superficial (Ms). Carecem, no entanto, evidências conclusivas sobre como essas alterações impactam o desempenho muscular e a performance mastigatória. Ensaios clínicos randomizados com maior número amostral e tempo de acompanhamento são necessários para confirmarem as alterações eletromiográficas nesses indivíduos.

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