Is apex position a determining factor in the orthodontic traction duration of unilateral impacted maxillary canines? A cone-beam computed tomography-based 3-dimensional study.

Introduction: This study analyzed the influence of the 3-dimensional (3D) root apex position on the traction duration of unilateral impacted maxillary canines, compared with the cusp tip position.

Methods: Thirty-one cone-beam computed tomography scans were analyzed. Each normally erupted canine was mirrored across the midsagittal plane to create an image of its enantiomorph. The distances were measured between the root apices of the impacted canine and the enantiomorphic contralateral normally erupted canine, as well as between their cusp tips and tooth angulations. Each distance variable was further subdivided into vertical displacement, horizontal displacement, mesiodistal (MD) displacement, and labiopalatal displacement, whereas the angulation variable was divided into MD tip difference and torque difference. The correlation between each measurement and the traction duration was analyzed.

Results: The position of the root apex showed no significant correlation with traction duration. However, the 3D displacement, horizontal displacement, and labiopalatal displacement of the cusp tip (P <0.001), vertical displacement of the cusp tip (P <0.01), and the 3D angulation difference and MD tip difference between tooth axes (P <0.05) showed a significantly positive correlation with traction duration. Multiple regression analysis showed that the 3D displacement of the cusp tip explains approximately 55.4% of the variance in traction duration, increasing by 1.2 months per 1 mm.

Conclusions: Although root apex position does not affect traction duration in unilateral impacted maxillary canines, the 3D displacement of the cusp tip is a key determinant, with more significant palatal displacement and a higher vertical position associated with longer traction duration.