We investigated the effects of proximity of the root apex to the maxillary labial cortical plate, palatal cortical plate, and incisive canal cortical plate on apical root resorption. Cone-beam computed tomography was used to measure the amount of root resorption and root apex movement around maxillary right and left central incisors in 30 adults who underwent four-bicuspid extraction followed by treatment with multibracket appliances. The patients were divided into three groups on the basis of the direction of root apex movement, after which the correlation between the amount of root resorption and root apex movement was determined. Mean apical root resorption was 1.80 ± 0.82 mm (range, 0.18-3.96 mm). The amount of root apex movement was positively correlated with the amount of root resorption on the side of pressure. Root apex proximity to the maxillary labial cortical plate, palatal cortical plate, and incisive canal cortical plate was associated with apical root resorption. Orthodontic treatment plans should carefully consider root proximity to the maxillary cortical plate. (J Oral Sci 58, 231-236, 2016).