Buccal Alveolar Bone Changes in Adult Non-extraction Clear Aligner Patients: A Retrospective CBCT Study

Abstract

Introduction: The aims of this retrospective study were to investigate maxillary and mandibularalveolar bone height and width changes associated with non-extraction Clear Aligner Therapy (CAT), and to identify risk factors associated with these changes. Methods: This retrospective study recruited adult aligner patients, aged 18-45. Based on widthchanges at the 1st premolars and 1st molars, arches were divided into maxillary and mandibular expansion (> 3 mm width increase at the 1st premolars OR 1st molars) or control (< 1.5 mm width increase at the 1st premolars AND the 1st molars) groups. A total of 84 arches (44 maxilla, 40 mandible) met the criteria for these 4 groups. Buccal alveolar bone height (BH) and thickness at 3mm (BW-3) and 6mm (BW-6) from the cemento-enamel junction (CEJ) were measured and assessed for changes at the central incisors, first premolars, and mesio-buccal roots of the first molars using CBCTs. Descriptive analyses were performed, and multivariate linear regression was conducted to identify predictors for the observed changes in alveolar bone height and width. Results: The maxillary and mandibular expansion groups exhibited the largest width changes at thefirst premolars, with mean values of 3.80 mm and 3.70 mm, respectively. Mean upper and lower central incisor labial movements and proclination were minimal (less than 1 mm and 3 degrees) in the expansion groups. The mean changes in the control groups were < 0.6 mm of expansion at the first premolars and molars in both the upper and lower arches, and less than 1 mm and 1 degree of labial movement and proclination at the central incisors. There was a strong correlation between arch width changes and buccal tipping of posterior teeth. For buccal alveolar bone height and width changes in the maxillary arch, the only significant difference between the expansion and control groups was a small change in BW-6 at the maxillary first molars (-0.16 mm). The greatest mean changes observed in the lower arch were the reduction in bone height at the lower incisors (-1.5 mm) and lower first premolars (-1.4 mm) in the expanded patients. There was almost 1 mm greater reduction in bone height at the first premolars of the expansion group compared to control group. Regression models controlling for age, gender and treatment time found that belonging to the expansion group and undergoing labial movement were associated with lower incisor bone loss. For the lower premolars, the strongest predictors for bone loss were increased premolar width and buccal tipping. Conclusion: The mean change in antero-posterior position and angulation of incisors in these mild tomoderately crowded Class I adult patients treated with CAT was minimal. Posterior expansion was accomplished primarily by tipping, and the teeth exhibiting the most expansion were the first premolars. Tipping teeth labially or buccally was most strongly associated with alveolar bone loss in the lower arch.