Is the third molar maturity index (I3M) useful for a genetic isolate population? Study of a Sardinian sample of children and young adults

This work aims to assess the validity of the cut-off value (0.08) of the third molar maturity index (I3M) for discriminating minors from adults in Sardinian population. A sample of 336 digital panoramic radiographs of healthy Sardinian children and young minors (165 females and 171 males), aged between 15 and 23 years (mean age, 19.35 years in females and 18.80 years in males), was retrospectively evaluated. The left lower third molars were analysed by applying a specific cut-off value of 0.08 determined by Cameriere et al. in 2008. The reliability and reproducibility of the test was also studied: the intra-class correlation coefficients (ICC) were 0.91 (95% CI, 0.89-0.93) and 0.88 (95% CI, 0.86-0.90), for the intra- and inter-observer reliability, respectively. The I3M gradually decreased as the real age gradually increased in both sexes. According to the pooled results of the diagnostic test, the accuracy (ACC) was 0.86 (95% CI, 0.82-0.89); the proportion of correctly classified subjects (Se = sensitivity) was 0.82 (95% CI: 0.76-0.86); and specificity (Sp = specificity) was 0.95 (95% CI, 0.89-0.97). The positive predictive values (PPV) and the negative predictive values (NPVs) were 0.97 (95% CI, 0.94-0.99) and 0.70 (95% CI, 0.62-0.77). The LR+ and the LR- were 17.12 (95% CI, 7.27 to 40.36) and 0.19 (95% CI, 0.14 to 0.25). In spite of this, significant differences in the early mineralisation of the third molar were found between sexes as well as in the results of the diagnostic test, showing a better sensitivity in males than in females. The results showed that, although the third molar teeth are highly variable in development, and with differences between females and males as compare to other teeth, the I3M is a reliable method to distinguish between minors and adults even in such a genetic isolate population.