It is important to discriminate minors from adult especially in the absence of documents to avoid criminal violations (Deitos et al. 2015). From this point of view, methods used for age estimation applied in forensic medicine must be accurate, precise, and well-validated before application (Rivera et al. 2017).
The estimation of dental age in Egyptians was reported in previous studies (El-Bakary et al. 2010; Zaher et al. 2011; El Morsi et al. 2015; Wahdan et al. 2017). But, to the best of our knowledge, this is the first Egyptian study that validates the use of the third molar maturity index cutoff value of 0.08 to discriminate those aged 18 years or older from minors (less than 18 years).
In his original study, Cameriere et al. (2008) evaluated the I3M in OPGs of 906 Caucasian Italian individuals aged between 14 and 23 years (53.6% females and 46.4% males). The cutoff value of 0.08 showed 70% sensitivity and 98% specificity with 83% correct classification. This cutoff value was tested in many populations around the world and showed high sensitivity and specificity although percentages were different.
Results of this Egyptian sample showed relatively faster development (earlier complete maturation of the third molar) in boys. Generally, many studies showed male precedence of the third molar development, e.g., Hispanics (Solari and Abramovitch 2002), Japanese (Olze et al. 2004), Serbian (Zelic et al. 2016), and Saudi (AlQahtani et al. 2017). Nevertheless, females were reported to show faster development of third molars in one study (Liversidge 2008).
When the cutoff value of “I3M = 0.08” was evaluated in the present study (247 cases), the high sensitivity (Se) of the test in boys (95%) but relatively lower sensitivity in girls (73%) was documented. Sensitivity values were reported to be over 95% in Turkish males (128 boys from 293 total sample) (Gulsahi et al. 2016), Colombians (288 children), (De Luca et al. 2016), and Serbians (598 cases) (Zelic et al. 2016). Meanwhile, it was 88% in Botswana (1294 individuals) (Cavrić et al. 2016) and 90% in Australians (143 cases) (Franklin et al. 2016). Unfortunately, sensitivity was only 52% in the Saudi population (300 cases) (AlQahtani et al. 2017).
Meanwhile, a high specificity (Sp) of the cutoff value (100% in boys and 97% in girls) was found in the present sample. On the other hand, specificity was 100% in the Turkish study (Gulsahi et al. 2016) and in Saudi males (AlQahtani et al. 2017), and over 85% in Colombians (De Luca et al. 2016), Serbians (Zelic et al. 2016), Botswana (Cavrić et al. 2016), and Australian population (Franklin et al. 2016).
It seems that values of sensitivity and specificity of the present study are more in boys ensuring previous published data in Serbians (Zelic et al. 2016). On the other hand, girls showed more values in a Colombian study (De Luca et al. 2016).
Different sensitivity and specificity in these populations may be either due to actual differences between them or differences in the age distribution and sample size, as well as dissimilarity among observers. However, the examination of the third molars may provide reasonable accuracy for the likelihood that a person is at least 18 years old (Acharya et al. 2014).
In the present Egyptian sample, the proportion of correctly classified persons was 97% in boys and 82% in girls, even better than 83% reported by Cameriere et al. (2008). More or less similar proportions of correctly classified individuals were reported in Turkish (97.6% for boys and 92.7% in girls) (Gulsahi et al. 2016), Serbians (95% in males and 91% in females) (Zelic et al. 2016), and Chileans (83%) (Cameriere et al. 2018).
Meanwhile, the positive predictive value (PPV) in the present Egyptian sample was 60% in boys and 59% in girls. Although the PPV is highly useful, it is sensitive to the prevalence of the positive test group (older age category) and can rarely be generalized beyond the study sample (Gulsahi et al. 2016). In a legal and forensic context, it is ethically safer to underestimate age than to overestimate age due to constitutional and judicial implications when involving a possible adult (Cavrić et al. 2016).
Technically, unacceptable errors can be detected if an adult was wrongly diagnosed as a minor (less than 18 years). They will get the full benefit of safeguarding through being children in care. However, if the reverse occurs and a minor was diagnosed as over 18 years, this is an ethically unacceptable error as it leads to violation of minors’ rights (Garamendi et al. 2005).
In the context of estimating a person’s age, none of the techniques can be used with high reliability when the person has completed his growth. However, from the legal point of view, it is often enough to indicate whether a person is an adult or a minor (Schmeling et al. 2008).