Comparison of root resorption severity after fixed and invisible orthodontic treatment in patients with four first premolar extractions: A retrospective study

Root resorption is a common and unavoidable complication of orthodontic treatment, with limited research on its pattern in extraction cases using clear aligners. This study compared the severity of root resorption between fixed appliances and clear aligners in patients who underwent 4 first premolar extractions. A retrospective analysis was conducted on 28 patients with Angle Class I and II malocclusion treated with fixed appliances (n = 14) or clear aligners (n = 14) from 2019 to 2025. The mean treatment duration was 37.93 ± 13.65 months. Root resorption was assessed for both groups involving 488 teeth for right and left first molar and anterior teeth until canine for both arches excluding first and second premolar using the relative root-to-crown ratio on panoramic radiographs and tooth movement was measured using cephalometric superimposition. Chi-square and Mann-Whitney U tests were used to evaluate group differences. The proportion of teeth with no root resorption was significantly higher in the clear aligner group (52.67%, 236 teeth; χ2 = 11.253, P = .010) compared fixed appliance group (42.86%, 192 teeth). For upper anterior teeth, the fixed appliance group had a notably higher rate of moderate-to-severe resorption (40.91%) compared to the clear aligner group (17.14%; χ2 = 33.651, P < .001). For upper first molars and lower first molars, the clear aligner group also showed higher proportions of teeth without resorption (upper first molars: 28 vs 20 teeth, χ2 = 11.333, P = .010; lower first molars: 36 vs 16 teeth, χ2 = 15.692, P = .001). In terms of tooth movement, only the vertical (Y-axis) movement of lower anterior teeth differed significantly between groups: 0.8814 ± 1.01909 mm (fixed appliances, 95% CI: 0.06107-1.82393) versus 1.1314 ± 0.70874 mm (clear aligners, 95% CI: 0.47595-1.78690; P = .017), with no significant differences in other directions (all P > .05). Fixed appliances may increase the risk of moderate-to-severe root resorption in anterior teeth due to continuous heavy forces, while clear aligners reduce severe resorption but require caution during vertical movements.