Validity of Demirjian 8 Teeth Method for Age Estimation by Orthopantomogram

The estimation of age is an important aspect in medico-legal practice. The need for age estimation has certain important reasons at certain specific age groups in the Indian context:

1. 12 years: children below this age are not liable for certain offences;
2. 14 years: a child cannot be employed below 14 years;
3. 18 years: determines the status of majority and the legally permissible age for marriage in females;
4. 21 years: the legally permissible age of marriage in males.

In 1973, Demirijian et al , introduced the method of age estimation based on the radiological appearance of the 7 teeth on the left side of the mandible. The demirijian method is widely used to estimate chronological age due to its simplicity, reproducibility and ease of standardization. The estimation of age is based on the developmental stages of teeth, taking into consideration associated calcification process. Moreover, tooth maturation is a better indicator of dental age than tooth eruption which is influenced by various exogenous factors such as infection, extraction, crowding and ankylosis.

The original Demirjian’s method excluded the third molar due to the variability in its development, eruption and anatomy. 4 However, the pitfall of its exclusion was that the age prediction by the original Demirjian’s method is not feasible after about 16 years of age, since by this age all the permanent teeth , except the third molar , would have completed their development. Therefore, the third molar offers the only reliable radiological parameter for age determination in the age group of 16–23 years. 5

In a study carried out by Mincer et al., it was concluded that the third molar may provide reasonable accuracy for the prediction that a person is at least 18 years of age, rather than giving the exact chronological age, due to the absence of any other marker in the late adolescence.

Chaillet and Demirjian modified their method to incorporate the third molar and developed a new maturity score based on a French population. Another major modification made in this study was that the stages of teeth were modified to include two additional stages of non-formation of tooth (Stage “0”) and crypt development (Stage “1”); furthermore, the stage of development were assigned numerals which were designated as 0–9 for easier calculation and developed a multiple regression formula based on cubic function which gave better reliability when the third molar was incorporated into the study. 6 In the present study , modified demirijian method showed positive correlation between mean chronological ( 16.1224 + 1.6025 yrs ) and dental age ( 15.2112 + 2.2654 yrs ) , although chronological age of males ( 16.3333 ± 1.41421 yrs ) was observed to be slightly more than females ( 16.000 ± 1.71270 yrs ).

Indian studies have shown overestimation ranging from 2 months to over 3 years.7,8 A meta analysis of 12 studies by Jayaraman et al., which employed the Demirjian’s method, found an average overestimation of age of patients by more than 6 months and suggested that this dataset should be used with caution in global populations.9 Consequently, the method’s adaptation to the local population was considered essential for optimal age prediction. Genetic influences, socioeconomic status, nutritional conditions, and dietary habits have been reported as the possible reasons for variations in skeletal and dental maturity among different populations and ethnic groups and different groups within the same population.

Acharya et al (2011) , who derived the formula which was used in the present study for age assessment, had deduced a MAE of 1.43 years, with 44% of samples within ± 1 year, 36% within ± 1.1 to ± 2 years, and 20% beyond ± 2 years , the sample size being 597. 2 In the present study, MAE (0.9114 years) for the overall sample was similar to the original study, with 30.61% subjects within 1 year of chronological age and 24.48% subjects beyond 2 years of the chronological age.

In the study conducted by Jayanth Kumar et al (2011), with a sample size of 121, the MAE for 58 % sample was within ± 1 year, and that for 10.75 % beyond ± 2 years 1 .CH Sai Kiran et al in their study (2015) conducted on 250 subjects found an error of 2 yrs in 20 % of the sample. 10 Rath H et al (2017) found that the MAE was 2yr error in 23.6 % in their study with a sample size of 106. 11 The MAE in the previous studies by Jayanth Kumar et al (2011) , CH Sai Kiran et al (2015) and Rath H et al (2017) was found to be 1.18 yrs , 0.83 yrs and 1.3 yrs respectively , which when compared to our study results (MAE = 0.9114 yrs) , proves that Demirijian method is a reliable and accurate method for age estimation of individuals in 16-18 years age group.

To conclude, the Indian formula was reliable in approximately 30% of our cases with the mean absolute error of the total sample being less than 1 year. The accuracy of age estimation was found to be better in 16-18 year age group as compared to younger age group, probably because of the better development of the third molar by this age. The drawback of our study was the comparatively small sample size.

The reasonably good results obtained in the present study assert the use of Demirjian’s 8 teeth method with Indian cubic functions in the local population. It is a worthwhile exercise to apply the Indian formulas locally within specific regions, possibly in larger samples. This would in future lead to the development of regional database in various populations.