Coronal Repercussions of the Maxillary Central Incisor Torque in the First Set of Aligners: A Retrospective Study

Coronal torque is one of the key factors in orthodontic treatment. An adequate torque value has an impact on aesthetics and soft tissue profile. The aim of this quantitative, comparative and observational longitudinal cohort study was to analyze the efficacy of the maxillary central incisor coronal torque in the Invisalign^® system and evaluate the relation between coronal torque movement and patient's facial biotype. In total, 27 patients were selected. The planned movements (TP) were obtained from the Invisalign Doctor Site^® using mathematical formulas that consider the T0 measurements. Pre-treatment (T0) and after full use of the first set of aligners (T1) scanners were evaluated using Geomagic^® Control X ^TM by superimposing T0 and T1 models using a transverse plane and the long axis of the tooth crown. IBM^® SPSS^® software was used for statistical purposes. We found statistically significant differences between T0 and T1 in pro-inclination and retro-inclination, as well as between achieved and planned values in pro-inclination (p = 0.011). We verified that hyperdivergent clinical cases presented higher mean values of coronal torque, and hypodivergent cases presented lower values. In pro-inclination, the differences between the planned and achieved values were greater in hypodivergent cases and smaller in hyperdivergent cases. In retro-inclination, the differences between the planned and achieved values were greater in normodivergent cases and smaller in hypodivergent cases. This study highlights that inefficacy is more accentuated in pro-inclination. Aligners are an effective tool for producing coronal repercussions of torque movement, being more effective in retro-inclination.