Exploring the potential of rapid maxillary expansion and masticatory muscle activity in unilateral posterior crossbite

Background: This systematic review and meta-analysis aimed to evaluate if rapid maxillary expansion improves the activity of the masticatory muscles (masseter and temporal) in patients with unilateral posterior crossbite. Material and Methods: Searches were performed in PubMed/MEDLINE, Scopus, Web of Science, Embase, Cochrane Library, and grey literature. A manual search of orthodontic journals was also performed. Randomized clinical trials or longitudinal prospective studies were eligibles. Meta-analyses were conducted using R software with the “Meta” package, applying mean differences with a 95% confidence interval. Risk of bias was assessed using the Newcastle-Ottawa scale, and evidence certainty was evaluated using GRADE. Results: Nine articles were included. Qualitative analysis showed that RME treatment in patients with unilateral posterior crossbite showed a positive correlation with improvement in masseter and temporalis muscle activity. Meta-analyses indicated a significant difference for all models of muscle activity after treatment with rapid maxillary expansion, except for the temporal muscle in the force exerted on the maximum voluntary clenching on cotton rolls. The studies showed low bias risk, and the evidence certainty for each analysis was generally low to very low. Conclusions: This investigation demonstrated the benefits of R rapid maxillary expansion in treating unilateral posterior crossbite and its potential therapeutic effects on the masticatory muscles.