BACKGROUND Although Rapid Maxillary Expansion (RME) has been used for over a century, its effect on upper airways has not yet adequately been assessed in an evidence-based manner. OBJECTIVE To investigate the volumetric changes in the upper airway spaces following RME in growing subjects by means of acoustic rhinometry, three-dimensional radiography and digital photogrammetry. SEARCH METHODS Literature search of electronic databases and additional manual searches up to February 2016. SELECTION CRITERIA Randomized clinical trials, prospective or retrospective controlled clinical trials and cohort clinical studies of at least eight patients, where the RME appliance was left in place for retention, and a maximum follow-up of 8 months post-expansion. DATA COLLECTION AND ANALYSIS After duplicate data extraction and assessment of the risk of bias, the mean differences and 95 per cent confidence intervals (CIs) of upper airway volume changes were calculated with random-effects meta-analyses, followed by subgroup analyses, meta-regressions, and sensitivity analyses. RESULTS Twenty studies were eligible for qualitative synthesis, of which 17 (3 controlled clinical studies and 14 cohort studies) were used in quantitative analysis. As far as total airway volume is concerned patients treated with RME showed a significant increase post-expansion (5 studies; increase from baseline: 1218.3mm(3); 95 per cent CI: 702.0 to 1734.6mm(3)), which did not seem to considerably diminish after the retention period (11 studies; increase from baseline: 1143.9mm(3); 95 per cent CI: 696.9 to 1590.9mm(3)). LIMITATIONS However, the overall quality of evidence was judged as very low, due to methodological limitations of the included studies, absence of untreated control groups, and inconsistency among studies. CONCLUSIONS RME seems to be associated with an increase in the nasal cavity volume in the short and in the long term. However, additional well-conducted prospective controlled clinical studies are needed to confirm the present findings. REGISTRATION None. FUNDING Australian Society of Orthodontics Foundation for Research and Education Inc.
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