Accuracy of the third molar index cut-off value for estimating 18 years of age: Validation in a Japanese samples

Aims: To evaluate the cut-off value of third molar maturity index (I 3M ) = 0.08 for discriminating minors from adults in Japanese population. Material and Methods: 276 panoramic radiographs of healthy Japanese subjects (139 girls and 137 boys) age range from 14 to 24 years were evaluated. Results: ICC (Intra-class correlation coefficient) for intra-rater and inter-rater agreement of I 3M was 99.6% (95% CI 98.6–99.9%) and 98.9% (95% CI 98.8–99.9%) respectively. The proportion of correctly classified in girls was 87% (95% CI 81–93%) and in boys was 91% (95% CI 87–96%). The sensitivity of the test in girls and boys was 84% (95% CI 77–92%) and 89% (95% CI 83–95%) respectively and specificity was 93% (95% CI 85–100%) and 96% (95% CI 90–100%) in girls and in boys. The PPV (Positive Predictive Value) was 87% (95% CI 69–95%) in girls and 92% (95% CI 74–98%) in boys. Conclusion: The results of the study show that I 3M is capable of discriminating adults and minors in subjects around legal age of 18 years old in Japanese population.