Identification of orthodontic patients at risk of severe apical root resorption.

INTRODUCTION Current information suggests that the major variation in orthodontic root resorption can be explained by differences in individual predisposition. Our aim was therefore to test the predictive value of the amount of maxillary incisor resorption about 6 and 12 months after bracket placement for the resorption at appliance removal. METHODS We measured tooth length of the maxillary incisors on digitally converted periapical radiographs, adjusted for projection errors, made before treatment (T1), about 6 months (T2) and 12 months (T3) after bracket placement, and at the end of active treatment (T4) of 267 prospectively enrolled orthodontic patients, and interpreted reduced tooth length as apical root resorption. Anatomic and occlusal parameters were scored on the T1 radiographs and study models. Anamnestic and treatment parameters were collected from standardized recordings in the charts. RESULTS The Spearman R for resorption of each incisor ranged from 0.61 to 0.76 at T2 vs T4, and from 0.77 to 0.88 at T3 vs T4 (P <0.001). Only 0.6% of the patients with no incisors with >1.0 mm of resorption at T2 and 0.5% of those with no incisors with >2.0 mm of resorption at T3 had at least 1 incisor with >5.0 mm of resorption at T4. Amount of resorption at T3 and maxillary tooth extraction were included in the final prediction model for resorption of the most severely affected central and lateral incisors at T4, with explained variances of 0.71 and 0.67, respectively. Treatment duration and time with square wires was not related to resorption (P >0.05). CONCLUSIONS Patients at risk of severe apical root resorption can be identified according to the amount of resorption during the initial treatment stages.