INTRODUCTION Root resorption is an undesirable consequence of orthodontic tooth movement. The severity is unpredictable, and, despite extensive research, the etiology remains unknown. Torque has been acknowledged as a risk factor for root resorption. The aims of the study were to evaluate and quantify the extent of root resorption after the application of 2.5° and 15° of buccal root torque for 4 weeks. METHODS Fifteen patients requiring bilateral extraction of their maxillary first premolars for orthodontic treatment were recruited to the study. By using a standardized experimental protocol, the right and left premolars were randomly subjected to either 2.5° or 15° of buccal root torque. At the end of the 4-week experimental period, the premolars were extracted. A volumetric analysis of root resorption was performed by using microcomputed tomography and measured with specially designed software. RESULTS Overall, the amounts of root resorption were comparable after the application of 2.5° or 15° of buccal root torque (P = 0.59). There was a significant difference between the 2 force levels only at the apical region (P = 0.034). More root resorption occurred in areas of compression than in areas of tension. The variables of age and sex were not statistically significant. CONCLUSIONS Root resorption was evident after 4 weeks of buccal root torque application. More root resorption was seen at the apical region than at the middle and cervical regions. Higher magnitudes of torque might cause more root resorption, particularly in the apical region. As shown in previous studies, the etiology of root resorption is multi-factorial and cannot be explained by mechanical factors alone.