Third molar development according to chronological age in populations from Spanish and Magrebian origin

Abstract

Spain is frequently the entrance country into the European Union for undocumented immigrants, especially those from the Magreb (Northern Africa). Forensic age estimates for these persons are difficult because systematic studies of dental maturity are lacking. Three different populations were analyzed to determine the pattern of development of third molars as a tool for age estimation in people of different ethnic and geographic origin. Orthopantomograms from two different populations of Spanish origin (Galicia in northwestern continental Spain, and Ceuta, a Spanish province in Northern Africa) were compared to radiographs of molars from a Magrebian population (Northern Africa) resident in Ceuta. Orthopantomograms were obtained from a private dental clinic (n = 344) in Galicia and from the Public Oral Health Services (n = 228) in Ceuta. We looked for differences in third molar mineralization (determined with the Demirjian scale) that might serve as age indicators (older versus younger than 18 years). Differences in maturation patterns were found between sexes and populations of origin. Mineralization of tooth 38 was more advanced in males than females among subjects 18 years of age and older in all three populations. Moreover, mineralization of tooth 38 in subjects aged 18 years and older was significantly slower in the Spanish-Galicia population than in the Magrebian-Ceuta population. We found no significant differences between Magrebian and Spanish individuals from Ceuta. We conclude that differences in tooth 38 mineralization may be related more with socio-geographical than ethnic origin (ancestry), and thus constitute evidence of the relevance of socio-geographic rather than genetic factors in third molar development. We used ROC analysis to determine the accuracy of the examiner's ability to correctly estimate age as younger or older than 18 years. The results suggest that Demirjian stage for tooth 38 can be considered a good indicator of age in all three populations.

Introduction

The fight against illegal immigration is one of the main problems affecting European Union (EU) border and immigration policies, especially since most European countries signed the Schengen treaty to eliminate internal border checkpoints and controls. Efforts to control illegal immigration need to strike a balance between decisions to deny the entry into the EU of citizens from non-Schengen countries, and the obligation to ensure the rights of those genuinely in need of international protection. For different reasons, including the strategic geographic location of Spain (the region of Andalusia is only 14 km from the northern coast of Africa, and the Canary Islands are close to its northwestern coast), Spain is frequently the entrance country into the EU for undocumented immigrants, especially those from the Magreb (North of Africa) and Sub-Saharan Africa. Some immigrants are minors subject to special Spanish and European Community regulations that differ from those applicable to subjects over 18 years old. Undocumented immigrants under 18 years old and without relatives in Spain are also subject to Spanish administrative regulations which place these minors under the guardianship of the Spanish authorities.

According to Spanish criminal law, subjects under 14 years old are exempt from criminal liability, minors between 14 and 18 years old are subject to special criminal standards and, in specific circumstances, persons over 18 but under 21 might be subject to the criminal standards applicable to minors under 18 according to the Spanish Minor Law [1]. In all such cases and according to Spanish criminal or administrative laws, the prosecutor or corresponding administrative authority has the obligation to establish the age of the purported minor. In these cases the assistance of a specialist in Legal Medicine may be required to help establish the biological age of the unidentified or undocumented person. Therefore, both in clinical settings and in the specific field of forensic medicine, there is a growing demand by the courts for appropriate medical tests aimed at estimating the approximate age of undocumented, presumed minors.

Forensic age diagnosis should comprise a physical examination, including anthropometric data, signs of sexual maturation, and potentially age-relevant developmental disorders, an X-ray examination of the left hand, and a dental examination which records dentition status and evaluates an orthopantomogram [2], [3], [4]. Moreover, X-ray examination of the medial clavicular epiphyseal cartilage [3], [4], [5] is of use to check whether the chronological age is over or under 21. Dental development correlates with different morphological stages of mineralization that can be observed in X-rays, comprises a more uniform and gradual set of changes than eruption, and may be less influenced by external factors (such as malnutrition, disease and mental stress) than other measurable criteria of maturity [6], [7]. However, the reliability of age estimates based on dental development is not uniform from birth to adulthood. After the age of 14 years, when most of the teeth are in the process of completing apical formation [8], dental age estimation becomes more difficult. The only teeth still growing after that age are the third molars, which are highly variable in their pattern of formation: agenesis is frequent, and the age of complete mineralization varies widely [8], [9], [10].

Several studies that explored the usefulness of the third molar as a reliable age indicator [4], [8], [11], [12], [13], [14], [15], [16], [17], [18], [19] have shown that dental development varies slightly between different populations [4], [11], [12], [13], [14], [15], [16], [17], [18], [19], making population-specific studies necessary. Features of the reference population such as genetic, nutritional and geographical factors must be taken into account in benchmark development; therefore, population-specific standards would enhance the accuracy of forensic age estimates based on maturation of the third molars in living subjects.

Some research in dental mineralization has been done in populations of Spanish origin [10], [14], [15]. However, most undocumented illegal immigrants in Spain are of Magrebian origin (North of Africa), and forensic age estimates for these persons are difficult because systematic studies of dental maturity in Magrebian populations are lacking, and accurate methods to assess chronological age are unavailable for this population [16]. Dental age estimates for these immigrants must be assumed to be of questionable accuracy, since until now they have been based on data for the Spanish population. To identify differences in the pattern of development of third molars between populations of different geographic and ethnic origin, we compared orthopantomograms from two populations of Spanish origin (Galicia and Ceuta) against radiographs from a Magrebian population resident in Spain (Ceuta). We also evaluated the ability of the age estimation method to identify individuals 18 years of age or older.