Apical root resorption in Class III patients following pronounced mandibular incisor retraction with lingual high precision fixed appliances: a retrospective cohort study

BACKGROUND: Extensive retraction of mandibular incisors in Class III treatment may increase the risk of orthodontically induced apical root resorption (OIARR). This retrospective cohort study aimed to assess the incidence and severity of OIARR in Class III patients treated nonsurgically with lingual high precision fixed appliances (HPFAs) and significant anterior tooth retraction. METHODS: Eligible for inclusion were adolescent and adult Class III patients treated with lingual HPFAs (WIN, DW Lingual Systems GmbH) and extraction of lower premolars, who completed treatment between 2015 and 2024. Pre- (T0) and post-treatment (T1) panoramic radiographs were measured for root and crown lengths, with relative root resorption (rRR, %) calculated for each tooth. Clinically relevant OIARR was assessed using the Malmgren index (scores 1-4). Statistical significance of mean rRR (%) changes was assessed using one-sample t-tests (α = 0.05). RESULTS: A total of 25 patients (mean age at T1 26.8 ± 9.7 years; 12 females, 13 males; mean Wits at T0 -6.7 ± 2.5 mm) and 350 mandibular teeth were analyzed. The mean rRR for anterior teeth was 3.15 ± 4.05%, with no cases of severe resorption (Malmgren score 4) and only 6.7% of roots exhibiting clinically relevant shortening (Malmgren score 3). There was no increased risk of OIARR in anterior teeth compared to premolars and molars (3.15% vs. 3.31%). CONCLUSION: Extensive bodily retraction of lower anterior teeth was not associated with significant OIARR in this Class III cohort. Excellent torque control using HPFAs enabled considerable retraction with low risk of OIARR, supporting this approach as a safe nonsurgical alternative for Class III camouflage.