We read the study “Apical root resorption due to mandibular first molar mesialization: a split-mouth study” by Winkler et al in the April 2017 issue of the AJO-DO . Mandibular molar mesialization is a difficult process because of the cortical nature of mandibular bone and the wide buccolingual roots of the mandibular molars. The split-mouth design mentioned by the authors was appropriate, since it nullifies various limiting factors such as the patient’s overall periodontal health and the clinician’s skill. As mentioned in the Discussion, orthodontic treatment improves the long-term prognosis of mesially inclined posterior teeth with appropriate biomechanics and no periodontal inflammation. However, as an addition, a record of measuring the pretreatment inclinations of the molars on orthopantograms and a comparison with their posttreatment positions could have given a better idea about the EARR associated with mesialization of molars. Clarification will be highly appreciated.