Transverse Dentoalveolar Changes with Clear Aligners in Mixed Dentition: A Systematic Review with Exploratory Meta-Analysis

Background: Transverse maxillary discrepancies during mixed dentition can negatively affect occlusal development and facial harmony. Clear aligners have been increasingly proposed as an interceptive alternative to traditional expansion approaches, but the extent and nature of the transverse dentoalveolar changes associated with their use in growing patients remain incompletely defined. While previous reviews have qualitatively explored this topic, no prior meta-analysis has been conducted to provide a quantitative synthesis of these changes in mixed dentition. Methods: A comprehensive electronic search was conducted for English-language studies published from January 2019 to April 2026 using the PubMed, Ovid MEDLINE, Web of Science, Embase, and Cochrane Library databases. The final database search was performed on 30 April 2026. Randomized controlled trials, prospective studies, and retrospective studies evaluating transverse maxillary changes in growing patients treated with clear aligners were included. Case reports, reviews, and studies involving syndromic patients or surgical interventions were excluded. Two reviewers independently performed study selection, data extraction, and risk-of-bias assessment. Furthermore, a meta-analysis of quantitative outcomes with sufficient comparability across studies was performed. Effect sizes were reported as standardized mean differences (SMDs). Results: From 40 screened records, a total of 7 studies were included in this review. The meta-analysis revealed a reasonably consistent trend toward increased transverse dimensions. The pooled SMDs were 0.685 (distal intermolar), 1.141 (mesial intermolar), 0.828 (transpalatal), 2.052 (intercanine transpalatal), and 1.541 (intercanine width). However, the magnitude of the effect remains uncertain because of the small number of included studies, methodological variability, heterogeneous outcome definitions, limited long-term follow-up, and substantial statistical heterogeneity observed for selected outcomes. Conclusions: The current evidence base reveals a reasonably consistent direction toward favorable transverse dentoalveolar changes with clear aligner therapy. However, the exact magnitude of the benefit remains uncertain due to methodological heterogeneity and the lack of robust long-term data. Due to the qualitative limitations of the included studies, the meta-analysis was intended to provide exploratory insights rather than definitive conclusions. Further high-quality studies with 3D imaging, standardized 3D outcomes, and long-term follow-up are needed to corroborate these results and guide clinical protocols.