Three-dimensional evaluation of root resorption risk factors in fixed appliances and clear aligners: A retrospective study

Objectives: The objectives of the study are to evaluate root resorption using three-dimensional reconstruction and quantify the effects of risk factors. Material and Methods: This retrospective study included 50 Class I extraction patients (27 fixed appliances and 23 clear aligners). Pre- and post-treatment cone-beam computed tomography and model/oral scans were used for 3D reconstruction of teeth and alveolar bone. Root resorption and tooth displacement were measured; potential risk factors, including appliance type, tooth position, and magnitude/type of movement, were analyzed. Results: The incidence and extent of root resorption were significantly lower in the clear aligner group (31.88%, 0.55 ± 0.07 mm) compared with the fixed appliance group (46.30%, 1.02 ± 0.09 mm). Among all tooth positions, lateral incisors demonstrated the highest incidence and greatest severity both in the clear aligner group (39.13%, 0.64 ± 0.13 mm) and the fixed appliance group (55.56%, 1.15 ± 0.16 mm). A strong positive correlation was observed between the incidence and extent of root resorption in both groups ( p < 0.001). Regional volumetric loss appeared to be associated with both the magnitude and type of tooth movement. For example, in the fixed appliance group, each 1 mm of root intrusion was associated with an average cervical-third resorption of 1.393 mm 3 in tooth 13 ( p = 0.023). Conclusion: Root resorption was associated with appliance type, tooth position, and tooth movement. Clear aligners were associated with more favorable root health outcomes in this retrospective study. Lateral incisors exhibited the highest incidence and extent of root resorption in anterior teeth. Root resorption was associated with both vertical intrusion and changes in torque.