CBCT Analysis of Maxillary Incisor Root Resorption and Incisive Canal Changes After Clear Aligner Therapy Considering Demographic and Skeletal Patterns

Root resorption, a common adverse outcome of orthodontic treatment, frequently affects maxillary incisors. This retrospective cohort study evaluates root resorption, changes in the morphology of the incisive canal (IC), and changes in the spatial proximity between the maxillary central incisors (U1) and the IC following clear aligner-based retraction in extraction cases. Demographic (age, sex) and skeletal (sagittal and vertical) factors were also considered.

A total of 80 central incisors from 40 patients of Chinese Han ethnicity (15 males, 25 females; mean age, 22.54 ± 7.25 years) who underwent treatment with clear aligners (Invisalign®, Align Technology, CA, USA) following bilateral first premolar extractions were retrospectively analyzed. Sagittal skeletal classifications were as follows: Class I (n = 15) and Class II (n = 25) patterns, as well as low- (n = 10), average- (n = 13), and high-angle (n = 17) vertical facial types. Cone-beam CT scans were assessed before (T1) and after treatment (T2) for IC dimensions, cortical bone width, root–IC distances, and U1 root length and width at three heights above the labial CEJ (H1: 2 mm, H2: 4 mm, H3: 6 mm). Statistical analyses included non-parametric tests (Mann–Whitney U, Kruskal–Wallis, Wilcoxon), Chi-square tests, and logistic regression to assess group differences, associations, and predictors.

The IC width and U1–IC distance decreased significantly in several subgroups, with females, adults, Class II patients, and those with high-angle patients showing the largest reductions. Root resorption was greater in females (1.13 ± 0.90 mm) than in males (0.53 ± 0.38 mm; p =0.029) and in Class II (1.06 ± 0.79 mm) compared to Class I (0.64 ± 0.76 mm; p =0.017). Closer post-treatment root–IC proximity was associated with higher resorption severity, particularly at the H1 level. Logistic regression identified U1 displacement as the most significant predictor of IC contact/invasion.

The findings reveal distinct biomechanical effects of clear aligners on IC morphology and root resorption, with a greater susceptibility identified in females, Class II patients, and those with high-angle malocclusions. Notably, we observed a gender-specific disparity in IC remodeling, with males exhibiting superior expansion and females showing apical reduction. Crucially, statistical modeling identified the amount of maxillary incisor retraction as the strongest predictor for root-IC contact or invasion. This risk, elevated in Class II and high-angle cases, underscores the necessity of skeletal-specific treatment plans, including CBCT evaluation and modified force protocols. Clinically, these results advocate for reduced retraction forces in high-risk groups to minimize root-IC approximation and associated resorption.

Clear aligner-based retraction of maxillary central incisors in extraction cases can significantly alter the IC–U1 relationship and increase the risk of root resorption, particularly in females, Class II patients, and those with high angles. Pre-treatment CBCT assessment, careful torque control, reduced retraction per stage, and lighter forces are recommended for high-risk profiles to minimize IC contact and resorption.