This study aims to analyze the predictors of root resorption in orthodontic treatment. From 407 records, 377 pretreatment and posttreatment periapical radiographs of permanent maxillary central incisors of 199 patients treated with fixed appliances were divided according to the apical morphologies: pipetteshaped, dilacerated, pointed, rounded and rectangular; crown/root ratio; and presence or absence of partial hypodontia. Changes in root length between the onset and completion of orthodontic treatment were measured in digitized images and statistically compared using T student, one-way ANOVA and Tukey tests. The apical morphology influenced the occurrence of root resorption; teeth with rounded and rectangular apical morphologies were more resistant to root resorption (.001 and .0007, respectively). Short teeth and the presence of partial hypodontia or multiple partial hypodontia did not present greater tendency to root resorption (.1008 and .1544, respectively). The results indicated that abnormal apical morphology is a predictor of external apical root resorption after corrective orthodontic therapy. However, short teeth and partial hypodontia did not increase the prevalence of apical resorption. The susceptibility or individual predisposition to tooth resorptions during orthodontic treatment may be related to the apical morphology
