Apical alveolar bone thickness predicts intrusion accuracy and proclination risk of mandibular incisors in clear aligner therapy: a pilot study

Mandibular incisor intrusion with clear aligners often shows limited predictability and undesirable inclination. This study aimed to explore exploratory prognostic associations between preoperative alveolar bone thickness and intrusion-related treatment outcomes. This retrospective exploratory study included 23 patients (92 mandibular incisors) treated with clear aligners. Six labial and lingual alveolar bone thickness parameters at the cervical, mid-root, and apical levels were measured based on pretreatment CBCT data. Outcomes including intrusion achievement rate (IAR) and proclination achievement rate (PR) were evaluated. Multivariable generalized estimating equations (GEE) analyses were performed to identify independent associations after adjusting for core confounding factors. Supplementary exploratory ROC analyses were conducted exclusively to observe dataset-based patterns without deriving clinical cutoffs. The cohort included 5 males and 18 females (mean age 25.22 ± 5.075 years), with Class I/II/III malocclusions (47.83%/52.17%/0%), two aligner systems (26.09% Invisalign/73.91% Angelalign), and a mean initial overbite of 6.30 ± 1.47 mm. After treatment, mean IAR was 44% ± 38% and mean PR was 124% ± 106%. Gingival recession occurred in 40.2% and prominent root contour in 70.7%. Apical lingual (RaLi) bone thickness was independently associated with IAR (B = 0.156, P < 0.05) and PR (B = -0.409, P < 0.05). ROC analyses yielded preliminary dataset-specific patterns but did not generate generalizable thresholds for clinical application. Preoperative RaLi demonstrated exploratory prognostic association with mandibular incisor intrusion and proclination outcomes in this limited cohort and warrants prospective validation.