Accuracy of predicting 18 years of age from mandibular third molar development in an Indian sample using Demirjian’s ten-stage criteria

Predicting 18 years of age can be crucial in forensic contexts. The third molar is the only tooth developing during this chronological period and has been used to estimate minority/majority status (</≥18 years). Conventionally, Demirjian’s grading has been used to assess third molar development although the method was not originally intended for evaluating this tooth. Demirjian incorporated third molar assessment in a recent modification and replaced the alphabetical grading (A to H) with a numerical scale (0 to 9). The new grading system is untested on third molars and this study assessed the tooth’s development on orthopantomograms of 221 Indian subjects (68 males, 153 females; age range 15–21 years). The tendency to correctly determine majority/minority status was assessed using three different statistical approaches, viz. traditional regression analysis, logistic regression analysis and Bayesian prediction. The sample was divided in to a reference sample of 180 cases and a test group of 41 subjects. All three statistical methods correctly predicted an individual as being </≥18 years in 73.2% of test subjects. Their ability to correctly identify a minor/juvenile was higher (85.7%) than their capacity to properly identify a major/adult (60%). Using the revised grading system, and irrespective of the statistical method applied, over one quarter of Indian subjects requiring identification as a major/minor were categorised in to the wrong age group. This level of accuracy may be inadequate for courts of law to rule with sufficient levels of certainty about the juvenile/adult status of an individual using third molar development.