Three-dimensional CBCT analysis of bone remodeling, root resorption, and incisive canal morphology during miniscrew-assisted aligner-based incisor retraction with and without extractions

Objectives This study aimed to investigate three-dimensional changes in incisive canal (IC) morphology, root–canal proximity, and root resorption following maxillary incisor (U1) retraction with clear aligners, comparing extraction and non-extraction treatment protocols. Materials and methods A total of 100 patients (200 U1) treated with clear aligners were retrospectively analyzed using CBCT before and after treatment. The extraction group included 40 patients and the non-extraction group 60. Linear measurements of IC width, root–canal distance, cortical bone width (CBW), IC height, and root length/width were obtained at three levels above the labial cementoenamel junction (H1–H3: 2, 4, and 6 mm). Volumetric and surface area analyses of the IC and U1 were performed to evaluate morphological and structural remodeling. Group differences and predictive factors for root resorption and canal contact/invasion were assessed statistically. Results Extraction-based retraction produced significantly greater reductions in canal width, CBW, and root–canal distance, with increased apical root resorption, most notably in patients who underwent substantial anterior retraction (all P 0.05). The mean decreases in root–canal distance were 1.08 ± 0.92 mm, 1.10 ± 0.91 mm, and 1.02 ± 0.99 mm at H1, H2, and H3, respectively, in extraction cases, vs. 0.40 ± 0.58 mm, 0.47 ± 0.78 mm, and 0.30 ± 0.98 mm in non-extraction cases. Apical root resorption averaged 0.91 ± 0.80 mm in the extraction group and 0.32 ± 0.56 mm in the non-extraction group ( P 0.05), correlating with closer root–canal proximity. Volumetric and surface area analyses revealed greater reductions in IC and U1 dimensions in extraction cases, indicating intensified bone remodeling. Treatment duration, incisor movement, IC height, and root–canal distance were significant predictors of canal contact, while root resorption correlated positively with treatment duration, incisor movement, and root length. Conclusion Extraction-based aligner retraction elicits greater osseous remodeling around the incisive canal and increased root resorption, particularly in cases requiring substantial anterior retraction, reflecting a coupled bone–tooth adaptive response to orthodontic loading. These findings highlight the dynamic nature of craniofacial bone physiology and emphasize the need for biologically guided treatment planning to minimize tissue stress and iatrogenic effects.