Demirjian’s and Cameriere’s methods for estimating the 18-year legal age threshold using third molar maturity in a Northern Thai population

This study evaluated and compared the accuracy of Demirjian’s and Cameriere’s methods for estimating the 18-year legal age threshold using mandibular third molar maturity in a Northern Thai population. It also aimed to establish population-specific cut-offs. A total of 260 orthopantomograms from healthy Northern Thai individuals aged 14–23 years were retrospectively collected. Bilateral mandibular third molars (teeth 38 and 48) were assessed using Demirjian’s stages and Cameriere’s third molar maturity index (I3M). Diagnostic indices and receiver operating characteristic (ROC) curves with area under the curve (AUC) values were used to evaluate performance and discriminatory ability at the 18-year threshold. Among Demirjian’s stages, only stage H demonstrated consistently high specificity (0.89–0.98) across sexes and tooth sides. Cameriere’s method also showed strong performance, with specificity for I3M < 0.08 ranging from 0.83 to 0.98 and increasing markedly when a stricter cut-off of I3M < 0.02 was applied, reaching up to 1.00 in males and 0.98 in females. ROC analysis indicated excellent to outstanding discriminatory accuracy in both sexes and on both sides of the mandibular third molars. These findings showed that Demirjian’s stage H and Cameriere’s I3M < 0.02 were useful methods for estimating the 18-year legal age threshold. The results highlight the importance of population-specific standards for forensic age assessment in the Northern Thai population.