Radiographic evaluation of third molars development in relation to chronological age among children and youth in Aden city

The only tool available to estimate the age of individuals is the third molar after puberty, which plays an important role in forensic science. This research aims at assessing an individual's chronological age based on the third molar's stage of dental growth according to Demirjian's model. A comprehensive cross-sectional sample of 950 orthopantomorgrams consisting of 530 with known age and sex and ranging from 16 to 23 years of age, was obtained from a Diagnostic Medical Center in Aden City/Yemen, between 2017 2018. The mean age at the early stage of development (A&D) was lower for males than females. Later growth in females in maxillary molars was the stage (E&G), but later in mandibular molars in males. Earlier in the four molars, the complete eruption of the third molar (H) stage was in females. There was a strong association between the developmental stages of maxillary molars in females and lower (right and left) molars and third molars in females between upper (right and left). As the results show that, in the case of completion of the roots of the third molars in stage (H), the likelihood of an adult being over 18 years of age in the case of full development wisdom is 100% in females when one molar or more was found, but it is 66.7% in males when one molar is present, and 100% when two or more molars are present. We concluded that the third stage of molar development is one of the few tools we can use to evaluate the age when the development is close to completion and it can be assumed that individuals with complete x-ray calcification of the third molar at (G – H) stages are over 18 years, while those at the (E-F) stages are probably under 18 years of age.


Introduction:
Estimation of forensic age is one of the key areas of forensic medicine and odontology science (30) . The number of unidentified corpses and human remains as well as the number of cases without age determination have increased over the past decade (10) . Various categories of biological have been identified (skeletal age, morphological age, secondary sexual age and dental age (25) ).
Age estimation is one of the most important factors used to determine an individual's identity, which is necessary not only in living cases but also in deaths for civil and criminal cases and is carried out for various reasons such as mass disasters, eg.fire accidents and crashes. In a living person, determining the age is vital in individuals without birth certificate, who are getting married, attending school, joining the army, employment and also in the determination of criminal liability such as in incidents, eg. rape, kidnapping, illegal immigration, premature births, orthodontic malocclusion, and pediatric endocrinopathy (22) .
The estimation of the actual age of individuals is one of the main challenges of forensic science. Various methods used today have been developed and tested to determine the age of young people and can be categorized into either non-medical procedures, including personal examination and identification documents, or medical procedures, including physical and radiological examinations or those having Medical procedures that include or combine physical and radiological assessments (11) . The physical exams involve anthropometric measurements, skeletal maturation, Univ. Aden J. Nat. and Appl. Sc. Vol. 24 No.1 -April 2020 estimate of dental age, combination of dental growth and anthropometric measurements and combination of skeletal and tooth eruption (30) .
Age estimation is one of the important responsibilities of medico-legal officers in recent times as crimes of a varied nature and age is an important factor in the determination of punishment in all these cases and age is inseparably linked in all these matters (13) ; such need exists, for instance, if no confirmed information is available on the age of a person suspected of having committed a criminal offence; the criminal law question at issue is whether the person concerned has exceeded the age of criminal responsibility and whether the general criminal law applicable to older minors or adults is to be extended (29) .
Estimation methods for dental age can be widely categorized based on the methodology used to assess the age and on the methods used to estimate the age as visual, radiographic, chemical and histological methods (28) . The teeth have long been recognized in the hands of a medico-legal expert as a valuable tool for personal establishment and identification, so the dental age is an indication of adolescent biological maturity. Demirjian first identified a method for determining dental age and is widely used and accepted mainly due to its ability to compare different ethnic groups (4) methodologies used to determine dental age are still the most sensitive means today (19) .
After about 14 years and since all the permanent teeth appeared, age estimation is difficult, except the third molars that would have completed their production making them the only reference used to measure their age (13) . The main criteria for determining the dental age of living individuals involved in criminal proceedings are the eruption and radiological analysis of the mineralization of third molars (2) .
Wisdom teeth development takes place within a certain period of time. The association between the growth of wisdom teeth and chronological age has often been used for several reasons such as beginning orthodontic treatment, age estimates or legal and anthropological purposes (6) .
Among young children, the dental age can be measured with greater accuracy. This is because most teeth are currently being formed and calcified. Nevertheless, after the early tens of most teeth have calcified and erupted except for the third molars, this makes the third molar growth the most appropriate option for age assessment from the late tens to the early twenties, thus making the third molars the most useful when it is necessary to determine an individual's juvenile or adult status when there is no clear report with the age reported (13) .
The third molars differ in position, morphology and timing of development, and sometimes they do not exist at all and can be larger than the 1st and 2nd molars with roots fused and delineated by vertical grooves. The maxillary molars generally consist of 3 cusps, whereas some show 4 cusps but in the mandible, the variation is around 4 and 5 cusps, and it is noted that the formation and eruption of the third molars occur faster in males than in females, contrary to the development of the other teeth in which girls mature earlier.
It was also noticed that the third molar maxillary appears to grow a little faster than its mandibular counterparts (16) .
In the age range of 16 -23 years, the wisdom teeth are the only teeth still in development and thus very critical for the assessment of dental age; but due to considerable variability in conception, position morphology and formation time, the reliability is questionable (8) .
The purpose of this analysis is to assess an individual's chronological age based on the third molar's dental development stages.

Material and Methods:
Cross-sectional description of 950 panoramic dental radiographs (orthopantomogram "OPG") was analyzed consisting of 530 males and 420 females obtained from Yemeni population with known age and sex attending the Diagnostic Medical Center (DMC) in Aden city / Yemen, for medical purposes (orthodontic treatment) during the period from January 2017 to December 2018. This panoramic radiographs was examined uniformly by dentistry and radiology doctors using an x-ray screen, as shown in Figure (1).
The inclusion criteria in the Yemen study individuals belong to the age group 16-23 years with age proof in the form of birth certificate. No history of clinical or surgical disease that could influence the existence and growth of third molars, while exclusion criteria were; history of injury or malnutrition, image deformity affecting vision of third molars, OPG showing clear dental pathology.
The study was based on the assessment of the third molar development stage proposed by the Demirjian, Goldstein and Tanners method (24) , which is the most popular and widely used method for evaluating the third molar mineralization (calcification) phases. According to the classification of the above method, 8 stages of (A-H), four stages of crown (A-D) and four stages of root development (E-H) were distinguished, as illustrated in Table (A) and Figure (2) (18,24) .
Each subject was registered with the identification number, gender, date of birth, and OPG. exam date; and the third molar eruption stages were determined. The chronological age has been determined from the date of birth and OPG in each individual student. The maturation stage of third molars (maxillary & mandibular) was obtained through OPG analysis. In addition, the upper and lower third molars were correlated with the radiographic appearances of the stage of the third molars. Both data were reported for statistical analysis by computer facility using the Statistical Package for Social Sciences (SPSS), descriptive statistics of the investigated variables presented in frequency and percentage mean, standard deviations (SD±), whereas the Pearson correlation test was used to determine the relationship between third molar calcification and age, and the statistical significance rate was taken as P <0.05, all data were presented in statistical tables.

Ethical consideration
Ethical approval has been taken from the Committee of Ethics in the Faculty of medicine and Health Sciences, University of Aden.

Results:
This study was conducted to detect the chronological age of an individual based on the third molar tooth development , Table (1) shows 950 Panoramic dental radiographs analyzed, of which 530 (55.8%) were males and 420 (44.2%) were females, of age between 16 to 23 years.   Table (3) displays the results of correlation between developmental stages of different molar teeth. There were significant positive correlation coefficients between different variables, particularly, between contralateral molars than antimeres. The highest coefficients of correlation were found in females (r=0.902) between right and upper eft third molars. Strong correlation was also found in females (r=0.855) the lower right and lower left third. In addition, there was a significant (relation between upper left and lower left molars in females (r=0.830) and right molars in females = 0.807) and upper right and upper left molars in males (r=0.806), the lowest coefficients between upper right and lower left molars in males was (r=0.561).

Discussion:
Age estimation by teeth growth has been used over a long period of time, which is a reliable statistical age indicator that tends to be independent of exogenous factors such as malnutrition or disease. However. Age estimation, based on dental method, has deficiencies, particularly during adolescence when the third molar is the only variable dental indicator left. A great variation in position, morphology and time of eruption exist. Some important deficiencies are the variations within population, different methodologies, and the difference between observers (10) .
In this study, the phase suggested by the method of Demirjian introduced a distinction separating eight stages of crown and root development in order to address some of these deficiencies. The method avoids any numerical identification of stages and is characterized by shape changes in panoramic views; thus irrespective of theoretical length estimates. This category seemed to be the most suitable for this study, while other studies dealing with age estimation were scarce as age predictors (19) .
In this study, in relation to (A-D) developmental stages of right maxillary and both mandibular molars and negligible earlier development of left maxillary molar in males than females , gender impact on the development of third molar has expressed a trend for significant earlier development in males than in females. On the other hand, males showed negligible earlier development of both mandibular third molars at the developmental stage (E-G) compared to females, while the opposite was observed in both maxillary molars in females showing negligible earlier development than males. This finding is in line with others studies of populations from Japan, Germany and Cauca's. Therefore, this result seems to be a unique finding for third molars, since for the other permanent teeth the root growth rate is faster in female. Concerning the stage of complete eruption (H) stage, significant earlier eruption of all molars was found in females than males. The present finding is in contrast with that obtained by Gunst et al. (10) who expressed earlier development in males than females, this disparity may have to do with different population and genetic factors (10) . Certain studies showed no significant variations at all stages of development in the third molar growth between males and females (1,13,23) , while others reported by different studies done in Iran, India, China and Turkey showed that the third molars erupts earlier in females than males (9,21,26,27) .
Leftright similarity in the third molars development age, represented by the correlation coefficient, was found to be higher in both maxilla and mandible, particularly in females where the highest correlation coefficient was observed between maxillary molars and both mandibular molars respectively, whereas males showed left to right maxillary symmetry only. This finding may be due to coincident development of the right and left sides of the arch that and is bilateral symmetry and is in harmony with that obtained by Sandra et al., Solari and Abramovitch, Wilershausen et al., (21,27,31,32) , this is in agreement with other studies which found no significant differences were revealed in third molars development between left and right side in all stage of development where both third molars were scorable and the development of third molars is faster in maxilla as compared to mandible (3,9,13) but others study done in Iran and Saudi population showed a significant difference between maxillary and mandibular teeth development which the mandibular third molars is more reliable than maxillary (17,27) .
For several possible combinations of fully developed wisdom teeth, the probability for a person older than 18 years was measured. Considering the location of wisdom teeth, 100% likelihood was observed in males for both upper right and lower right molars and in females for all molars. However, if the number of fully developed wisdom teeth is considered, 100% probability of an individual being older than 18 years was found in both sexes. The present finding, therefore, answers the question of whether a person is already 18 years of age by high degree confidence and considered as an adult. This finding is substantiated by Garamendi et al. (7) and another study done in Portugal that found females and males reach the age 18 years in stages (G) and (H) respectively (14) , in other studies done in Turkey and Japan, the mineralization of third molars are the same in both sexes (12,20,21) , wereas other studies on population from China, Saudi Arabia, Australia and Indonesia showed that the age 18 years is reached in stage (H) in males earlier than females (5,9,15,26,32) .