Fractal analysis of alveolar trabecular bone changes after orthodontic treatment: a retrospective comparison of extraction and non-extraction protocols

Previous studies investigating the association between orthodontic treatment and changes in alveolar trabecular bone (ATB) have reported inconsistent findings, and limited evidence is available comparing extraction and non-extraction protocols in both the maxilla and mandible using a standardized fractal analysis (FA) approach. The aim of this study was to evaluate the association between tooth extraction during orthodontic treatment and fractal dimension (FD) values of the ATB using FA. Measurement reliability was assessed using intra- and inter-examiner intraclass correlation coefficients (ICCs). A total of 162 orthopantomograms (OPGs), comprising 81 pre-treatment (T0) and 81 post-treatment (T1) images, were retrospectively collected. Patients were categorised into three treatment protocols: maxillary first premolar extraction, mandibular first premolar extraction, and non-extraction treatment. FD measurements were subsequently evaluated according to the anatomical region analysed. Standardised regions of interest (ROIs; 35 × 35) pixels were placed in the posterior alveolar bone region. FA was performed using ImageJ software (Version 1.54 g, National Institutes of Health, Bethesda, MD, USA) to quantify FD values of the ATB. Treatment-related changes in FD were calculated as ΔFD = T1 − T0. Intragroup changes were analysed using the Wilcoxon signed-rank test, and intergroup differences were evaluated using the Mann–Whitney U test ( p < 0.05). Measurement reliability was excellent (intra-examiner ICC = 0.931; inter-examiner ICC = 0.899). A total of 81 patients were included. Baseline demographic characteristics and FD values were comparable among the study groups ( p > 0.05). The mandibular extraction group showed the greatest increase in FD, whereas the mandibular non-extraction group showed no significant within-group change. Both maxillary groups exhibited reductions in FD. Jaw-specific comparisons showed no significant difference in ΔFD between the maxillary extraction and non-extraction groups ( p = 0.200), whereas ΔFD differed significantly between the mandibular extraction and non-extraction groups ( p < 0.001). Orthodontic treatment was associated with significant changes in radiographic FD values of ATB. The magnitude and pattern of these changes varied according to treatment protocol and anatomical region, with the greatest alterations observed in the mandibular extraction group. Further prospective studies using three-dimensional imaging are needed to clarify the biological significance of these findings.