Changes in Teeth Root Angulation During Retention Following Non-Extraction Fixed Orthodontic Treatment in Growing Patients

Abstract

Achieving stable occlusion following orthodontic treatment is essential, and root angulation serves as one of the determining factors. Given that adolescents still possess remaining growth potential, retention plays a particularly important role in maintaining post-treatment outcomes and ensuring long-term stability. This study aimed to evaluate post-treatment changes in the root angulation and root parallelism of maxillary premolars and first molars in adolescents who completed non-extraction orthodontic treatment, to determine whether such changes occur during the retention phase and to assess their potential clinical significance. The experimental group comprised 55 adolescents (25 males, 30 females) who underwent fixed orthodontic treatment of the maxilla without extractions and wore removable retainers. A control group of 34 untreated adolescents (13 males, 21 females) with Class I occlusion and no crowding was included for comparison. A total of 193 and 132 panoramic radiographs were analyzed for the experimental and control groups, respectively. Tooth angulation was defined as the mesial angle between the long axis of each maxillary posterior tooth and a reference line connecting the bilateral infraorbital margins. Temporal changes over time were analyzed using scatter plots, quadratic trend lines, and Pearson correlation coefficients. Intra-examiner reliability was excellent (ICC = 0.991 ‒ 0.998). Most maxillary posterior teeth in the treated group showed significant negative correlations between time and angulation (p < 0.0001), with slopes of -0.02° to -0.08° monthly, indicating progressive reduction in angulation. In the control group, slopes were smaller (-0.01° to -0.03° monthly) and generally non-significant. Absolute angular differences between adjacent teeth in the treated group decreased slightly but significantly over time, most notably between the first and second premolars (slope = -0.02° monthly, p < 0.0001), suggesting improved inter-tooth parallelism. No meaningful changes were observed in the controls. Overall, root angulation of maxillary premolars and first molars continues to change after non-extraction orthodontic treatment in adolescents, with a gradual trend toward reduction in angulation and improved inter-tooth parallelism. This indicates that retention following the non-extraction fixed orthodontic treatment may help guide adolescents with remaining growth toward more intimate and stable occlusal relationships during the retention period.