Aim: To assess apical root resorption (ARR) after Class II malocclusion treatment with the Forsus FRD and fixed technique and to identify the possible risk factors retrospectively. Material and Methods: Seventy-three Class II patients (52 females, 21 males; mean age 14.26±1.28 years) treated with Forsus FRD and fixed technique in the department of Orthodontics were included in this study. The crown and root lengths of 1368 teeth were measured from the panoramic radiographs taken at the

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... and the end of the treatment from these patients. ARR was calculated as the root-crown ratio (RCR) and relative changes of RCR (rRCR). Apical displacement of the incisors was assessed by the superimposition of the lateral cephalograms taken at the beginning and the end of the treatment. Besides, the effect of age, gender, treatment period, tooth type, and apical displacement on ARR was evaluated. Data were statistically analyzed. Results: ARR was detected in 66 (90.41%) patients and 228 (16.67%) teeth. ARR was mild (90≤rRCR<100%) in 181 (13.23%) teeth, moderate (80≤rRCR<90%) in 30 (2.19%) teeth, and severe (rRCR ≤80) in 17 (1.24%) teeth. Severe ARR occurred mostly in the upper central and lateral teeth. A significant negative correlation was found between rRCR and, age and tooth type (p<0.05). Conclusion: Orthodontic treatment of Class II malocclusion with Forsus FRD and fixed technique could lead to mild ARR in the majority of the patients. ARR is mostly seen in the incisor teeth and increases with advanced age.