A retrospective study of planned and achieved rotational changes of maxillary canines with clear aligner therapy

This retrospective study aimed to assess the accuracy of planned moderate-to-severe rotation changes (≥5°) of maxillary canines with the Invisalign (Align Technology, Tempe, Ariz) appliance. The secondary aim was to evaluate the influence of the planned rotation direction on the accuracy.

Digital models representing the initial malocclusion, the planned occlusions, and the achieved occlusions after the wear of an initial series of Invisalign aligners by adult patients were measured using metrology software. A method to define rotation directions was formulated. The sample was then divided into 5 categories by rotation type: mesial-in, mesial-out, distal-in, distal-out, and combination rotations. This categorization enabled subsequent analyses to determine whether the planned rotation directions were met and whether rotation direction influenced accuracy.

A total of 114 maxillary canines from 75 patients satisfied the inclusion criteria. Overall, the mean accuracy of the planned rotation was 64%. Rotation direction had no statistically significant influence on the accuracy of the planned rotations. Planned rotation directions were achieved in 77% of the maxillary canines evaluated. Combination rotations demonstrated the greatest variability, with 51% rotating in a direction other than that planned. A 1° increase in rotational velocity per aligner correlated with a 5.35° shortfall in the accuracy of this rotation (P < 0.05).

The achieved rotation of maxillary canines after the wear of an initial series of Invisalign aligners differed from the planned movements in both magnitude and direction for planned rotations of ≥5°. A method for classifying rotation types was developed, which may facilitate further research to guide clinicians and optimize treatment outcomes.