Prediction of traction time for the alignment of impacted maxillary canines

To identify which factors influence the traction time of impacted maxillary canines using a combined orthodontic-surgical approach and to create a multivariate model to predict canine traction time.

Patients undergoing traction of impacted maxillary canines by a single orthodontist were selected. Seventy patients (mean age ± SD): 19.32 ± 8.81) meeting the inclusion criteria were enrolled in the study. They had 89 impacted canines (69 palatally displaced and 20 in a buccal position). Variables that could be related to orthodontic treatment as a whole and to impaction and its treatment were recorded for each patient. The treatment predictors were explored by univariate Cox regression and multivariate generalized linear mixed models (GLMM). A multivariate analysis was performed using a mixed-effects parametric survival analysis (MMPSA) Weibull model to assess the contribution of each of the predictive variables and to create a multiple linear regression model to explain canine traction time.

Cox regression showed significant association between traction time and age (p = 0.013) and the number of failed appointments (p < 0.001). An MMPSA Weibull model to build a predictive model based on the Akaike information criterion (AIC) showed that interceptive maxillary expansion significantly reduced traction time (p = 0.002). In contrast, traction time increased with a wider angle of the impacted canine relative to the midline, with missed appointments, and with radiological overlap with lateral or central incisors.

The orthodontic treatment time to align impacted maxillary canines increases with radiological overlap with lateral and central incisors, a wider angle to the midline, the absence of interceptive maxillary expansion, and missed appointments.