International Journal of Legal Medicine

, Volume 130, Issue 4, pp 1109–1120 | Cite as

Third molar maturity index (I3M) for assessing age of majority in a black African population in Botswana

  • Jelena Cavrić
  • Ivan Galić
  • Marin Vodanović
  • Hrvoje Brkić
  • Jelena Gregov
  • Serena Viva
  • Laura Rey
  • Roberto Cameriere
Original Article


Assessment of legal age, also known as age of majority, is a controversial issue as there are few body biomarkers or evidence during late adolescence differentiating a subject from being a minor or adult. The third molar was recognized as a suitable site for age examination in late adolescence. We analyzed the development of the left mandibular third molar by the third molar maturity index (I3M) and a specific cut-off value of I3M = 0.08, established by Cameriere et al. in 2008 and used it for discriminating between minors and adult black Africans from Gaborone, Botswana. A final sample of panoramic radiographs (OPTs) of 1294 people (582 males and 712 females) aged between 13 and 23 years was evaluated. The real age decreased as I3M gradually increased. There was no statistically significant difference in the third molar development evaluated using I3M between males and females (p > 0.05) across different I3M classes. Results of 2 × 2 contingency tables for different cut-off values indicated that I3M = 0.08 was useful in discriminating between adults and minors. Precisely, for I3M = 0.08, the values of accuracy or overall fraction of correctly classified were 0.91 in males with a 95 % confidence interval (95 % CI) of 0.88 to 0.93 and 0.92 (95 % CI, 0.90 to 0.93) in females. Values of sensitivity of the test or the proportion of participants being 18 years and older were 0.88 (95 % CI, 0.87 to 0.90) in males and 0.88 (95 % CI, 0.90 to 0.93) in females, while values of specificity or proportion of individuals younger than 18 who have I3M <0.08 were 0.94 (95 % CI, 0.91 to 0.96) in males and 0.96 (95 % CI, 0.94 to 0.98) in females. Positive predictive values of the test, where the participants whose I3M <0.08 were adults, were 0.94 (95 % CI 0.91 to 0.96) in males and 0.97 (95 % CI, 0.94 to 0.98) in females, while negative predictive values of the test, where the participants whose I3M was ≥0.08 were minors, were 0.88 (95 % CI 0.85 to 0.90) in males and 0.97 (95 % CI, 0.94 to 0.98) in females. The likelihood ratios of the positive test (LR+) were 13.67 (95 % CI, 9.21 to 21.02) in males and 23.73 (95 % CI, 14.20 to 42.28) in females, while likelihood ratios of the negative test (LR−) were 0.12 (95 % CI 0.10 to 0.16) in males and 0.12 (95 % CI, 0.11 to 0.15) in females. Bayes post-test probabilities, p, were 0.94 (95 % CI 0.90 to 0.98) in males and 0.97 (95 %CI, 0.93 to 1.00) in females. These results indicate with high accuracy that I3M may be a useful alternative method in legal and forensic practice to discriminate individuals of black African origin who are around the legal adult age of 18 years in Botswana. Further studies should address the usefulness of this method and specific cut-off for different adolescent populations.


Botswana Legal medicine Third molar maturity index Accompanied minor Age estimation Age of majority 


Compliance with ethical standards

The study was conducted in accordance to the ethical standards laid down by the Declaration of Helsinki [55]. The approval for the study was granted by the Human Research and Development Committee (HRDC) of the Ministry of Health in Botswana and by the Ethical Council of the School of Dental Medicine at the University of Zagreb. Jelena Cavrić and Ivan Galić equally contributed to this article.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  1. 1.Henry M. Goldman School of Dental MedicineBoston UniversityBostonUSA
  2. 2.Departments of Research in Biomedicine and Health and Dental MedicineUniversity of Split School of MedicineSplit,Croatia
  3. 3.Department of Dental AnthropologySchool of Dental Medicine, University of ZagrebZagrebCroatia
  4. 4.School of Dental Medicine, University of ZagrebZagrebCroatia
  5. 5.Dipartimento di Civilta e Forme del SapereUniversity of PisaPisaItaly
  6. 6.AgEstimation Project, Institute of Legal MedicineUniversity of MacerataMacerataItaly

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