Clear Aligners in Extraction-Based Orthodontic Treatment: A Systematic Review and Meta-Analysis

This systematic review and meta-analysis aimed to evaluate the predictability of tooth movement, and clinical effectiveness of clear aligners in extraction-based orthodontic therapy. A comprehensive search of seven electronic databases (PubMed, EMBASE, Scopus, Cochrane Library, Web of Science, CINAHL and ProQuest) was conducted up to April 19, 2025, adhering to PRISMA guidelines. Eligible studies included prospective and retrospective designs assessing clear aligner treatment in patients aged ≥ 12 years with premolar extractions. Primary outcomes encompassed predicted versus achieved tooth movement and root angulation/parallelism, with secondary outcomes including treatment duration and clinical indices (American Board of Orthodontics Objective Grading System [ABO-OGS], Peer Assessment Rating [PAR]). Risk of bias was evaluated using the Swedish Council on Technology Assessment in Health Care (SBU) grading system and Centre for Reviews and Dissemination (CRD) criteria. Random-effects meta-analyses were performed for homogeneous outcomes. Twenty studies (536 aligner patients, 173 fixed appliance patients) were included. Meta-analyses revealed significant discrepancies between predicted and achieved movements, including excessive mesial tipping of maxillary first molars (mean difference: -6.08°, 95% CI: -7.89 to -4.26). Under-retraction (-1.93 mm, 95% CI: -2.15 to -1.71), and increased vertical displacement of maxillary incisors. Root divergence and anchorage loss were prevalent. Compared to fixed appliances, aligners exhibited inferior root control and occlusal contact scores. Four randomised controlled trials provided high-quality evidence, but the predominance of retrospective studies contributed to a moderate risk of bias. Clear aligners demonstrate biomechanical limitations in achieving precise root control and bodily movement in extraction cases, necessitating strategic overcorrections and adjunctive mechanics. Trial Registration: PROSPERO (CRD42024613540).