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

To evaluate the cut-off value of third molar maturity index (I_3M) = 0.08 for discriminating minors from adults in Japanese population.

276 panoramic radiographs of healthy Japanese subjects (139 girls and 137 boys) age range from 14 to 24 years were evaluated.

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.

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.