Abstract
Molar development is widely accepted as a reliable indicator of chronological age in a forensic context. A quantitative method for age estimation has been proposed by Cameriere et al. based on the relationship between chronological age and the third molar maturity index (I3M), which is the ratio between the two apical pulp widths and the total tooth length. Cameriere’s cut off value of 0.08 was found to be a reliable tool in assessing the threshold of 18 years of age. The aim of this study was to evaluate the accuracy of the I3M in different ethnic populations focusing on its specificity (subjects correctly classified as <18 years based on I3M >0.08) and sensitivity (subjects correctly classified as ≥18 years based on I3M <0.08). A review of 22 scientific articles was performed, representing data from panoramic radiographs of 12,286 individuals (5723 males and 6563 females) from all over the world, including some ethnical subgroups. The I3M showed an overall sensitivity for both sexes ranging from 51.8% to 93.4% and a specificity ranging from 86.2% to 100%. The proportion of correctly classified individuals ranged from 74% to 95%. These results can be useful to refer the age estimation with the margin of error of subjects correctly classified as minors (specificity) or adults (sensitivity), according to sex, ethnicity and geographical distribution. The I3M can be considered a suitable method for estimating adulthood in forensic settings, regardless of sex. However, ethnic group can affect the accuracy.
Introduction
Forensic age estimation in the living is crucial in criminal and civil proceedings, such as for refugee and asylum seeker procedures, human trafficking, child pornography, old-age pension and competitive sports.
1
The determination of adult or juvenile status is a scientific and legal challenge that forensic professionals need to solve using reliable methods.
2
According to the recommendations issued by the Study Group on Forensic Age Diagnostic (AGFAD) and Forensic Anthropology Society of Europe (FASE), chronological age estimation of a living person should consist of:
a physical inspection for recording anthropometric data, signs of sexual maturation and any age-relevant developmental disorders; X-rays of the left hand for the assessment of bone maturity or conventional radiography/computed tomography of the medial epiphysis of the clavicle if the skeletal development of the wrist is completed; and a dental examination and an orthopantomogram for the assessment of dental maturity.1,3–5
Regarding dental age estimation, methods commonly applied in adolescence are based on tooth development compared to a set of developmental stages charts,6,7 while in late adolescence such an estimation is based on the crown and root features of the third molar, such as Demirjian’s system. 8
The mineralisation of permanent teeth is very helpful until the age of 15–16 years, when second molars have also finished their development.6,7,9 However, in many countries, 18 years is the age of majority at which the individual is generally defined as an adult. 10 With specific reference to this threshold of adulthood, third molars are the last teeth to complete their development, and therefore they represent the best dental indicators of legal age.11,12 In fact, the development of third molars takes place between 14 and 23 years of age, during a specific age span from late adolescence to early adulthood, when their mineralisation is completed in most healthy individuals.6,7,9,13,14
Mincer et al. 15 first recommended the use of the molar development as an estimator of chronological age in forensic context using Demirjian’s system.8,15 More recently, Cameriere et al. 16 developed a method for estimating age among Caucasian people and discriminating adults and minors based on the relationship between age and the third molar maturity index (I3M). The I3M is defined as the ratio between the two apical pulp widths and the total tooth length. 17 According to this approach, a cut-off I3M value of <0.08 was determined in order to assign an individual as an adult age ≥18 years with a 95% confidence interval. The left inferior third molar is recommended for the measurements and assessment of I3M due to its longer duration of development. 16 In this regard, it is well known that the root growth in the third upper molar finishes earlier than the lower one.6,7,9,16 Cameriere’s I3M showed a better specificity (the proportion of subjects correctly classified as <18 years based on I3M >0.08) compared to Demirjian’s stage G in adolescence and a better sensitivity (the proportion of subjects correctly classified as ≥18 years based on I3M <0.08) compared to Demirjian’s stage H for adult age. 16 Furthermore, the use of the I3M method can be particularly suitable when used in conjunction with the other skeletal maturity markers. 18
However, the application of Cameriere’s I3M is strongly dependent upon the presence of the third molars, which may be congenitally absent or surgically removed.17,19 Unfortunately, if the root development of the third molar is complete, there is no possibility of measuring the open apices, and therefore the I3M is always <0.08 (adult). Therefore, the possibilities of using this method for assessing the age of majority are limited by the variable duration of the third molar’s development. There are also a wide range of factors associated with the timing of maturation, including genetic, biological and environmental influences, which can affect the time of appearance and progression of maturity indicators. 20 Based on the variability in geographical distribution of dental maturity and physical development according to ethnicity, nutrition and socio-economic status, the aim of this study was to evaluate the accuracy of Cameriere’s method as applied to different populations, and the sensitivity and specificity of the I3M cut-off value (0.08) in discriminating adults and minors.
Methods
A critical literature review was conducted independently by two examiners. Studies evaluating the accuracy of Cameriere’s I3M method 17 were derived from the following electronic databases: PubMed, Scopus, ISI Web of Science and System for information on Grey Literature in Europe (SIGLE).
Exclusion criteria were studies not having primary data (editorials, literature reviews, commentaries, case reports, letters), studies where I3M was compared to other age estimation methods, studies not reporting data on sensitivity and specificity of the I3M cut-off value and studies not in English. No filters were applied for the date of publication.
Two examiners independently provided an initial selection of articles to determine whether they might potentially fit the inclusion criteria. Disagreements were solved between the two examiners; if no agreement could be reached, it was resolved using a third co-author as a reviewer.
A data extraction sheet was developed and for each selected study, and the following items were recorded: first author’s name, year of publication, study’s country, sample size (overall, male and female), age range, sensitivity, specificity and accuracy (overall, male and female when available).
Results
The search of PubMed, Scopus, ISI Web of Science and SIGLE databases provided a total of 973 articles. Of these, 951 studies were discarded because they did not meet the inclusion criteria following review (studies in English with primary data on sensitivity and specificity of the I3M cut-off value).
A total of 22 research studies were identified and were included in the critical literature review.2,12,16,19,21–38 In Table 1, the main findings of the 22 studies are summarised, including country, sample size (male and female), age range, sensitivity, specificity and data accuracy according to sex and 95% confidence interval.
Data from selected articles showing sensitivity, specificity and accuracy.
The 22 studies cover a huge population, from five continents of the world, including Africa, Asia, Australia, Europe and South America. The three great human races (white, black and Asian) are also represented, including some ethnical subgroups such as Latino Americans,25,29,30 black and white Africans,22,26,28 Saudi Arabians, 21 Indians, 2 Chinese 27 and Japanese. 38
The total number of individuals recruited in the analysed studies was 12,286 (5723 males and 6563 females) mostly with an age range of 14–24 years. The geographical distribution of the individuals was: 6324 from European countries (Albania, Croatia, France, Italy, Sardinia, Kosovo, Montenegro, Netherlands, Poland and Serbia), 1554 from South America (Brazil, Chile and Colombia), 1830 from Asia (China, India, Saudi Arabia, Turkey and Japan), 2434 from Africa (Botswana, Libya and South Africa) and 143 from Australia.
The dental maturity of the above study group assessed by the I3M showed an overall sensitivity for both the male and female samples ranging from 51.8% (Saudi Arabia) 21 to 93.4% (Colombia) 29 and a specificity ranging from 86.2% (Brazil) 30 to 100% (Libya and Turkey).28,32 Regarding the proportion of individuals correctly classified as ≥18 years of age (I3M <0.08), it is worth mentioning that the second lowest value of sensitivity after the one reported in the Saudi Arabia population (51.8%) 21 was found in Chile (70.5%). 25 The overall proportion of correctly classified individuals was between 74% (Saudi Arabia) 21 and 95% (Turkey). 32
In Figure 1, the distribution of sensitivity, specificity and accuracy calculated for each country is represented by histograms.

Distribution of sensitivity, specificity and accuracy by country.
In terms of sex, for the male sample only, the sensitivity ranged from 52.3% (Saudi Arabia) 21 to 96.2% (Kossovo) 33 and the specificity from 85% (Australia) 31 to 100% (Saudi Arabia, Libya and Turkey).21,28,32 For the female sample, the sensitivity was between 51.3% (Saudi Arabia) 21 and 95.1% (Colombia), 29 and the specificity was between 67.2% (Brazil) 30 and 100% (Libya and Turkey).28,32 Unfortunately, three studies did not provide data according to sex analysis, and they were from South Africa, 22 Chile 25 and Italy.12,35
In terms of geographical distribution, for the European population, the lowest sensitivity value was 78.3% found in Holland, 19 while the highest was 91% reported in Serbia. 36 The minimum and maximum values of specificity were 92.1% in Poland 34 and 98.3% in Kossovo, 33 respectively. The overall proportion of individuals correctly classified (accuracy) ranged between 85.1% (Sardinia) 35 and 93% (Serbia). 36 For the African countries, the minimum and maximum values of sensitivity were 80% in South Africa 22 and 90.7% in Libya, respectively. 28 The specificity range was between 95% (Botswana and South Africa)22,26 and 100% (Libya), 28 while the accuracy ranged between 90% (South Africa) 22 and 94.8% (Libya). 28 For the Asian population, the sensitivity ranged from 51.8% (Saudi Arabia) 21 to 90.2% (Turkey), 32 the specificity from 94.5% (Japan) 38 to 100% (Turkey) 32 and the proportion of individuals correctly classified from 74% (Saudi Arabia) 21 to 95% (Turkey). 32 In Latin American populations, the sensitivity ranged from 70.5% (Chile) 25 to 93.4% (Colombia), 29 the specificity from 86.2% (Brazil) 30 to 92.2% (Colombia) 29 and the accuracy from 83% (Chile) 25 to 92.4% (Colombia). 29
Discussion
The demand for forensic age determination in living individuals is growing all over the world. According to the 2017 Global Trends Report, by the end of the 2017, 68.5 million individuals had been identified as having been forcibly displaced throughout the world as a result of feared persecution, internal conflicts or generalised violence. 39 About 3.1 million people asylum seekers are still waiting for a decision on their application, and 173,800 are unaccompanied minors. 39 Moreover, in developing countries, only half of children younger than five years of age have birth certificates. 40 For individuals with no valid proof of birth date (also known as legal age), age estimation is therefore crucial, and it represents one of the main requests made by police and judicial authorities. 19 There is wide agreement in the literature that the most appropriate approach to legal age estimation of a living person must include the assessment of somatic and sexual maturity as well as of skeletal and dental maturity by radiographic examinations.3–5,41,42 Dental growth and emergence have long been recognised as the most useful criteria, especially in adolescents and young adults, and several methods are available.8,15,16 Unfortunately, the margin of error can be substantial, even when using combined methods.3,43 In fact, no method is able to estimate age 100% precisely. 32 An error in estimating legal age can result in a child being treated as an adult, or an adult as a child. 44 According to the FASE and AGFAD recommendations, the estimates should necessarily refer to the margin of error or the possible range of variation around the mean associated with the particular method adopted. 3 Cameriere’s method provides such a margin of error for males and females according to their geographical distribution. In this regard, the I3M can provide reliable support for chronological age assessment.14,19 The proportion of individuals correctly classified as ≥18 years of age (I3M <0.08) is >70.5% in all countries, except for the Saudi Arabia sample (51.8%). 21 This can be considered as poor sensitivity if compared to the higher specificity of the I3M cut-off value ranging from 86.2% (Brazil) 30 to 100% (Libya and Turkey).28,32 However, this is a relevant result considering that, based on the present critical review, the high proportion of subjects correctly classified as <18 years of age (based on I3M >0.08) is fully consistent with the principles of medical ethics. It has been emphasised 16 that from a forensic perspective, the discrimination performance of any age estimation method should have better specificity than sensitivity, reducing the risk of overestimating the chronological age of adolescence. Based on inaccurate estimates, authorities could incarcerate minors in adult detention centres, which are unsafe and inappropriate for children, not protecting children from child labour or early marriage.10,41 Minors must be treated as children, with the full benefit of safeguarding through being children in care. 18 Therefore, within a forensic context, it is ethically better to underestimate the age of an individual because of the judicial implications involving a possible adult.
The overall results show a lower sensitivity of 84.3% and higher specificity of 94.4% compared to a previous meta-analysis (94.6% and 88.8%, respectively) that did not include nine recently published research studies19,22,23,25,33–35,37,38 dealing with the application of the I3M to other ethnical subgroups (e.g. Chinese, Japanese, South African and Chilean people). Of course, the I3M has some limitations mainly related to its variation in position, morphology and development.6,7,9 Such limitations should be underlined in any expert opinion in order to protect the person from the risk of overestimation.
The results of this meta-analysis show that Cameriere’s I3M is easy to use and practical for forensic practitioners, with a slight risk of under-estimation in both sexes. The I3M method also shows good reliability and reproducibility in the main ethnic groups and different subgroups according to their geographical distribution. In fact, the cut-off value (0.08) is a reliable and valuable threshold for discriminating adults and minors (high specificity in both sexes for every population studied), even in geographically isolated populations. It is worth mentioning that positive results of reliability and reproducibility were also found in a unique population such as Sardinians, known as one of the most extreme in its relative lack of heterogeneity. 35
Actually, it is not fully understood how ethnic origin can influence tooth development. A comparative study of wisdom tooth mineralisation has been carried in white, Asian and African populations on the basis of Demirjian’s stages. 45 Based on their results, the authors recommended the use of population-specific standards in order to enhance the accuracy of forensic age estimation. 45 In this regard, the I3M method can be applied all over the world, according to the margin of error of living subjects correctly classified as minor (specificity) or adults (sensitivity) found in each country for males and females.
Conclusion
Forensic science evidence is closely linked to the rates at which examiners make errors.46,47 The I3M provides such error rates for males and females according to the geographical distribution of population spread across five continents. The risk of overestimating the legal age of adolescence is pretty low using the I3M method, but inaccurate estimates of chronological age cannot be excluded according to the overall results of sensibility and specificity. Although the I3M is a suitable method in forensic settings, examiners must be careful in any legal age assessment, keeping in mind the known rate of error of such evidence and its probative value.
Footnotes
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.
Funding
The authors received no financial support for the research, authorship and/or publication of this article.
