What evidence exists for myofunctional therapy with prefabricated appliances? A systematic review with meta-analyses of randomised trials

Objective: To assess the treatment efficacy/efficiency with prefabricated myofunctional appliances (PMA) for children with malocclusion. Data sources: Nine databases searched without limitations till July 2019. Data selection: Randomised trials comparing PMAs to functional appliance treatment or no treatment. Data extraction: Study selection, data extraction and risk of bias assessment were done in duplicate. Data synthesis: Random-effects meta-analyses of mean differences (MDs) or relative risks (RRs) with their 95% confidence intervals (CIs) were conducted on seven publications (three published and one unpublished trials; 232 patients; 53% male; mean age 10.2 years). Compared to no treatment, one trial indicated that PMAs were somewhat effective in reducing overjet (MD -2.4; 95% CI -3.3 to -1.5), reducing overbite (MD -2.5; 95% CI -3.2 to -1.8), reducing mandibular crowding (RR 0.4; 95% CI 0.2-0.8) and establishing Class I canine relationship (RR = 2.3; 95% CI 1.1-4.9). However, compared to custom-made functional appliances, three trials indicated that PMAs were less effective in reducing the ANB angle (MD 0.9; 95% CI 0.5-1.4), increasing mandibular ramus length (MD -2.2; 95% CI -2.9 to -1.51), reducing overjet (MD 1.5; 95% CI 0.9-2.1), establishing a solid Class I molar relationship (RR 0.3; 95% CI 0.2-0.7), reducing the nasolabial angle (MD 5.8; 95% CI 0.8-10.8) and reducing facial convexity (MD -2.6; 95% CI -4.3 to -0.9). Finally, the quality of evidence was moderate to low due to risk of bias. Conclusions: PMAs are more effective in reducing overjet, overbite, mandibular crowding and establishing Class I canine relationship than no treatment. However, compared to custom-made functional appliances, PMAs are less effective in producing dental, skeletal or soft-tissue changes, even though they are less costly.