External Apical Root Resorption with Clear Aligners Versus Fixed Appliances: A Scoping Review of Comparative Evidence, Treatment-Related Factors, Imaging Modalities and Consistency of Reported Data

Most meta-analyses report less external apical root resorption (EARR) with clear aligners (CAs) than fixed appliances (FAs), but pooled differences are sub-millimetric and rest on few recurring studies. This scoping review (PRISMA-ScR) mapped how 2020–2026 evidence on CA–FA comparisons, treatment-related factors and imaging modalities was generated, and checked data consistency, without pooling. Its unregistered protocol (version 1.0) was reconstructed during manuscript preparation. PubMed, Scopus and Web of Science were searched; paired reviewers screened 1688 records and 263 full texts and included 176 reports (174 studies). Fifteen reports, including eight of 32 direct-comparison reports, were excluded because outcome data were not attributable to a distinct sample or not identifiable; in one, pooled by six syntheses, aligner values equal another study’s fixed-appliance values. Of 21 included comparisons, 17 had serious or high risk of bias, one accounted for clustering and three reported measurement error in millimetres; differences were 0.01–1.12 mm except in one. Fifteen of 17 studies not described as randomised reported less EARR with CAs; the only concealed-allocation trial of appliances alone found no difference. Two imaging comparisons disagreed on whether panoramic radiography under- or overestimates EARR. Differences should be judged against measurement error and design, and data consistency should be checked before pooling.