Revisiting the incisor index for sex determination: development of cut-off values and validation of predictive accuracy

Abstract

Objective: Sex estimation is a fundamental step in forensic human identification. Teeth are highly resistant to postmortem degradation and therefore provide valuable biological markers for sex determination. Among odontometric methods, the incisor index has long been recognized as a simple tool for sex assessment; however, the absence of clearly defined cut-off values has limited its practical application. This study aimed to establish cut-off values for the incisor index and to evaluate its predictive accuracy for sex determination in a Thai population.

Materials and Methods: The study was conducted in two sequential phases. In the first phase, mesiodistal crown widths of maxillary and mandibular incisors were measured and used to calculate the incisor index. Receiver Operating Characteristic (ROC) curve analysis was applied to determine optimal cut-off values using both Youden’s index and the Euclidean index. In the second phase, the predictive accuracy of these newly-derived cut-off values for sex classification was evaluated.

Results: Males exhibited greater mean mesiodistal tooth widths than females for all incisors, although statistically significant differences were observed in only four teeth. The highest predictive accuracy was obtained from the maxillary left incisor index with a cut-off value of 85.60, yielding an overall accuracy of 71.00%. The maxillary right incisor index demonstrated a similar performance with an accuracy of 70.00%. In contrast, mandibular incisor indices showed substantially lower predictive accuracies, all below 55%. These findings indicate that the discriminative potential of the incisor index depends primarily on the proportional relationship between central and lateral incisors rather than on their absolute dimensions.

Conclusion: The maxillary incisor index demonstrates moderate accuracy for sex estimation and may serve as a simple and practical tool for preliminary forensic assessment. However, the variability observed between dental arches highlights the importance of developing population-specific standards when applying incisor indices for forensic sex determination.