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, wherethe 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 cutoff
for different adolescent populations.