Cortical Bone Thickness and Success of Temporary Anchorage Devices in the Mandibular Buccal Shelf: A Retrospective...

Temporary anchorage devices (TADs) have revolutionized orthodontic treatment by providing reliable skeletal anchorage; however, their success on the mandibular buccal shelf remains highly dependent on local bone architecture. This study aimed to evaluate the success rate of TADs placed on the mandibular buccal shelf and to determine optimal cortical and total bone thickness thresholds using preoperative cone beam computed tomography to achieve high success rates.

This retrospective cohort study included 90 patients aged 18-35 years with an average growth pattern with 180 TADs placed bilaterally in the mandibular buccal shelf area. Cone beam computed tomography scans were analyzed for cortical bone thickness, total bone thickness, and cortical-to-cancellous ratio in the first and second molar regions at depths of 4, 8, and 12 mm from the cemento-enamel junction. Two independently calibrated examiners performed the measurements. Statistical analyses included receiver operating characteristic curves, binary logistic regression, and Kaplan-Meier survival analysis.

The overall success rate of TAD was 82.2% (148/180). The second molar region at 8 mm depth showed the highest cortical bone thickness (5.1 ± 1.3 mm) and yielded the best predictive performance (area under curve = 0.82). A cortical bone thickness threshold of 4.9 mm at this site resulted in a 93.6% success rate. Success was significantly higher with larger device diameter (2.1 ± 0.3 mm vs 1.8 ± 0.4 mm) and higher insertion torque (24.1 ± 5.2 Ncm vs 15.8 ± 4.5 Ncm). Kaplan-Meier analysis revealed 96.9% survival at 24 weeks when the cortical thickness was ≥4.9 mm compared to 72.0% when the cortical thickness was below this threshold (log-rank p < 0.001). Multivariate regression confirmed cortical thickness, total bone thickness, insertion site, device dimensions, and torque as independent predictors.

Preoperative assessment of cortical bone thickness using cone beam computed tomography provides valuable guidance for selecting optimal insertion sites for TADS in the mandibular buccal shelf. Incorporating this approach into routine treatment planning may improve the predictability and clinical success of orthodontic anchorage.