A retrospective cohort study on orthodontic outcomes and root resorption in mandibular crowding: interproximal reduction versus mandibular incisor extraction

Background/objective This study compared one-year post-treatment stability between interproximal reduction (IPR) and mandibular incisor extraction (MIE) using American Board of Orthodontics – Objective Grading System (ABO-OGS) criteria, which is a standardised method used to evaluate the quality of orthodontic treatment outcomes. Root resorption was also assessed as a secondary objective. Materials and methods A retrospective cohort study was conducted at a tertiary care hospital. ABO-OGS scores and root resorption were evaluated using dental casts and cone-beam computed tomography radiographs. A total of 40 patients (20 per group) were included. Due to the non-normal distribution of the data, as confirmed by the Shapiro-Wilk test, the Wilcoxon signed-rank test and Mann-Whitney U test were used for statistical comparisons. Results One year post-treatment, the median ABO-OGS score was higher in the IPR group (38.20; IQR: 34.30, 43.65) than the MIE group (43.50; IQR: 40.0, 46.0), with a significant difference of 5.3 points (p = 0.048). MIE resulted in greater root resorption (median difference: 2.0 mm; p = 0.042). Conclusions While MIE provided superior initial alignment, IPR demonstrated better long-term stability and was associated with less root resorption. These findings highlight the importance of individualised treatment planning in orthodontic care.