Meta-analysis shows clear aligners produce less skeletal expansion than conventional appliances in growing patients

BACKGROUND: Maxillary transverse deficiency is one of the most common issues encountered in orthodontic practice. Ideally, intervention should take place before the midpalatal suture has completely ossified, in order to take advantage of the patient's active growth. In recent years, treatment with clear aligners has emerged as an alternative to fixed appliances, offering a new way to achieve expansion in paediatric patients. OBJECTIVES: This systematic review aimed to analyse the predictability of movements induced by clear aligners in maxillary expansion, and to compare the effectiveness of the Invisalign First® system with conventional expansion appliances. SEARCH METHODS: A systematic review was conducted by searching PubMed-Medline, Scopus, Embase, Web of Science and Cochrane databases. ELIGIBILITY CRITERIA: Retrospective and prospective studies, as well as one randomised clinical trial, published between January 2021 and October 2025, which answered the PICO question, were included. DATA EXTRACTION AND SYNTHESIS: The quality of the included studies and the risk of bias were assessed using ROBINS-I (Risk of Bias in Non-randomised Studies) and ROB2 (Risk of Bias 2). For the quantitative analysis, heterogeneity among the included studies was quantified using the I statistic, and the results were presented in a forest plot. The Trim and Fill method was used to assess publication bias. RESULTS: Following a review of 267 publications, 15 studies were ultimately included in the review, and seven in the meta-analysis. Statistically significant differences were reported for the following variables: intermolar distance (6-6) ( - 1.77 mm; -2.57; - 0.97 95%CI; - 4.35 Z-test, p < 0.0001); total palatal volume ( - 460.63 mm; - 738.32; - 182.94 95%CI; - 3.25 Z-test, p = 0.0011); and arch perimeter ( - 1.75 mm; - 2.71; - 0.80 95%CI; - 3.59 Z-test, p = 0.0003). These results indicate that aligners produce significantly less skeletal transverse expansion than conventional expanders. CONCLUSIONS: Clear aligners appear to be capable of producing maxillary expansion, mainly through dentoalveolar changes that are more evident in the anterior region and at the level of deciduous teeth. In patients presenting with more pronounced transverse deficiencies, conventional expanders seem to achieve greater skeletal and posterior transverse changes. However, given that most of the current evidence derives from retrospective studies with moderate risk of bias, these conclusions should be interpreted cautiously and confirmed by well-designed prospective research. REGISTRATION NUMBER: CRD420250608558.