Comparison of cone-beam computed tomography and panoramic radiography in estimating the 18-year age threshold with the third molar maturity index: a retrospective study

Background The third molar maturity index (I3M) method, introduced for application on panoramic radiographs, is used to assess whether an individual has reached the legal 18-year age threshold. This study aimed to evaluate the applicability of the I3M method to cone-beam computed tomography (CBCT) scans and to compare the results with those obtained from panoramic radiographs of the same patients. Methods Patients who had already received both CBCT scans and panoramic radiographs were selected retrospectively. The maturity index values of 418 mandibular third molars were obtained via measurements via both CBCT scans and panoramic radiographs. The accuracy of the I3M method for both radiological methods was evaluated via receiver operating characteristic (ROC) curve analysis. The sensitivity, specificity, misclassification rate, positive predictive value (PPV), negative predictive value (NPV), positive likelihood ratio (PLR), negative likelihood ratio (NLR), and overall area under the ROC curve (AUROC) at the 95% confidence interval (CI) level were calculated as performance measures for both imaging modalities. Results Both imaging modalities showed excellent diagnostic performance, with AUROC values of 0.928 for CBCT and 0.932 for panoramic radiography. The sensitivity of CBCT was 82.0%, the specificity was 89.7%, and the misclassification rate was 14.1%. For panoramic radiography, the sensitivity was 85.1%, the specificity was 86.8%, and the misclassification rate was 18.1%. The PLR and NLR values for CBCT were 7.96 and 0.20, respectively, whereas those for panoramic radiography were 6.43 and 0.17, respectively. Additionally, the PPV and NPV values for CBCT were 0.943 and 0.705, respectively, and those for panoramic radiography were 0.930 and 0.738, respectively. Conclusions The results indicated that the accuracy of the I3M method for CBCT scans was similar to that for panoramic radiographs from the same individuals. Importantly, the I3M method used to estimate the legal 18-year age threshold can also be used for CBCT scans, as it enables the use of existing CBCT images in age estimation studies.