CBCT-Based Assessment of External Apical Root Resorption in Clear Aligner Versus Fixed Orthodontic Therapy: A...

Background/Objectives: External apical root resorption (EARR) is a recognized biological consequence of orthodontic tooth movement. Although clear aligner therapy has been hypothesized to reduce EARR due to staged and intermittent force delivery, existing evidence remains heterogeneous, particularly with respect to imaging modality. This systematic review and meta-analysis aimed to compare EARR between clear aligners and fixed orthodontic appliances using exclusively quantitative cone-beam computed tomography (CBCT)-based linear root length measurements. Methods: A systematic search was conducted in PubMed/MEDLINE, Scopus, Web of Science, Embase, CENTRAL, ClinicalTrials.gov, WHO ICTRP, and Google Scholar (inception to January 2026). Comparative clinical studies reporting CBCT-based linear root length changes (mm) in clear aligner and fixed appliance groups were included. Random-effects meta-analysis (DerSimonian-Laird method) was performed to calculate pooled mean differences (MD = CA - FA). Heterogeneity was assessed using Cochran's Q and I² statistics. Risk of bias was evaluated using the ROBINS-I tool, and certainty of evidence was assessed with GRADE. Results: Six studies involving 392 patients met the inclusion criteria and were included in the quantitative synthesis. Random-effects meta-analysis demonstrated significantly lower EARR in the clear aligner group compared with fixed appliances (MD = -0.50 mm; 95% CI -0.79 to -0.21; p < 0.001). Between-study heterogeneity was moderate (I² = 60.8%). Subgroup analysis suggested a larger reduction in extraction-based protocols, although data were limited. Sensitivity analyses confirmed the robustness of the overall effect. The certainty of evidence was rated as low. Conclusions: Clear aligner therapy was associated with lower CBCT-measured external apical root resorption compared with fixed orthodontic appliances; however, this finding should be interpreted with caution due to the limited number of studies, moderate heterogeneity, and potential residual confounding inherent to non-randomized designs. The results should be considered exploratory rather than definitive.