Background:Torque loss of maxillary central incisor teeth occurs frequently during space closure with clear aligners (CA).The aim of this study was to analyse the percentage reduction in upper incisor lingual inclination and risk factors for upper incisor angle after Invisalign treatment in extraction cases.
Methods:Records were obtained from 52 patients (average age 27.6 years) who initiated with Invisalign at four different orthodontic practices. Data was collected from cephalometric radiographs, doctors' case notes, and CA Web site databases. All patients who were treated with CAs were divided into maxillary incisors Lingual tipping (L) and non-maxillary incisors Lingual tipping (NL) groups based on whether U1-NA(°) was less than 17.1 (Mean -1 SD). Cephalometric data before and after therapy were analysed using a paired t-test. Differences between the L and NL groups were examined through independent sample t-tests, chi-square tests, and Wilcoxon rank sum tests. Correlation factors, including CC difficulty scores, age, gender, pre-treatment upper central incisor inclination, skeletal classification, divergence, orthodontist, treatment length, and refinements number, were identified using univariate and multivariate linear regression analysis.
Results:After treatment, 61.5% of the patients experienced upper incisor lingual inclination. Significant differences were observed between the groups in terms of the number of refinements, treatment length, and age (P<0.05). The number of refinements was directly proportional to the duration of treatment. A statistical difference was observed between orthodontists and the number of refinements. However, adolescents had significantly less refinement. A multivariate linear regression analysis revealed negative correlations between age (P=0.002), treatment length (P=0.002), and different orthodontists (P=0.013) with the reduction of the upper incisor angle after treatment.
Conclusions:The upper central incisors exhibit torque loss in extraction cases treated with Invisalign. The risk of a reduction in the angle of the upper incisors after treatment is increased by factors such as the patient's age (older patients), longer treatment times, and young orthodontists. It is recommended that these factors be closely monitored and guided during clinic visits.