The accuracy of estimating chronological age from Demirjian and Nolla methods in a Portuguese and Spanish sample

Age determination has great importance in many clinical decisions, being commonly used in pediatrics, legal medicine, forensic sciences, anthropology, odontopediatrics and orthodontics [1, 2, 12, 13, 15, 16, 29, 31, 41, 42]. Increased immigration and mixing of populations, due to the globalized economy resulting from the increased migratory flow, sets legal problems of various orders, with increasing importance of determining the chronological age of children, youths and young adults. So estimating chronological age is important in assessing the legal adult age of people without documents for judicial purposes, in determining growth and somatic development, in orthodontic treatment and in the area of anthropology to estimate the age of past populations from immature skeletal remains [1, 2, 5, 6, 12, 13, 15, 16, 29, 31, 49].

Dental and bone age have been assessed to determine to what extent they are correlated for diagnostic purposes. Considering that states of dental mineralization are much less affected by environmental [2, 11, 46] and hormonal [2, 23, 28] variations than states of bone mineralization, dental development provides more reliable indications of chronological age than bone development [2, 13, 30]. Various methods have been proposed to calculate chronological age through dental maturity and mineralization, among which we highlight those proposed by Nolla in 1960 [43] and by Demirjian et al. in 1973 [11].

The Demirjian method [11] is one of the most frequently used in estimating chronological age due to its simplicity, intra-examiner agreement, ease of standardization and ability to be reproduced, having been used and tested across a wide range of populations (e.g. [13, 15‐17, 20, 29, 34, 38, 42, 50]. Various studies described in the literature have found the need for the method to be adapted to the populations in which it has been studied [36]. Rózelo-Kalinowska et al. [45] compared the dental age of 994 healthy Polish children from 6 to 16 years old with the development patterns proposed by Demirjian, finding that the method overestimated chronological age, with overestimation being more evident in 11-12-year-old girls and 13-year-old boys. Chen et al. [8] assessed the applicability of the method in 445 Chinese children between 8 and 16 years old, also finding overestimation of age. Qudeimat and Behbehani [44] tested the method with 509 healthy Kuwaiti children, finding they showed a delay in relation to the French-Canadian children used in the original study by Demirjian et al. [11]. Bagherpour et al. [1] tested the accuracy of the method with 170 girls and 114 boys in Iran, finding overestimation of age in boys of 0.34 years and 0.25 years in that of girls, despite concluding the method was appropriate for estimating age, especially in the 9 to 13-year-old sample. Then Jayaraman et al. [28] concluded that the method underestimated age by 0.24 years in a sample of 266 Chinese orthopantomographs. More recently, Sarkar et al. [46] analyzed the effectiveness of the method with a sample of 100 Indians between 5 and 24 years old, finding underestimation of age of 1.63 years in boys and 1.54 years in girls. Djukic et al. [13] assessed the accuracy of the Demirjian and Willems methods with 686 Serbian children between 4 and 15 years old, finding that both methods showed a discrepancy in relation to chronological age, although the Demirjian method was less accurate than that of Willems. Khorate et al. [30] found an underestimation of around 2 years of chronological age in a sample of 500 orthopantomographs of individuals between 4 and 22 years old in the State of Goa (India).

Besides the Demirjian method, this study analyzes the predictive capacities of the Nolla method [43] as it has shown itself to be very accurate with a sample of Spanish and Portuguese participants [48]. The Nolla [43] method has been one of the least frequently used and tested across populations, despite its effectiveness [4, 24, 47, 48]. This method has already been tested with children between 3 and 15 years old in Sweden [24], Finland [47], and Andalusia [4], giving a high correlation using a limited number of teeth (teeth 21, 46 and 43 for boys and 21, 47 and 46 for girls under 10 years of age). Holtgrave, Kretschmer, and Müller [27] also found high accuracy of the method, finding no significant differences between dental age and chronological age in girls (in boys the method overestimated chronological age). The study by Bolanos et al. [4] showed that the most reliable teeth for estimating chronological age through the Nolla method varied between boys and girls. Caro and Contreras [7] found greater reliability using this method in determining dental age in permanent teeth, in comparison to three other methods. With a sample of children of Bangladeshi and British Caucasian origin between 3 and 17 years of age, Maber et al. [38] found underestimation in all age groups, although more pronounced for girls and increasing particularly after 10 years old. Miloglu et al. [40] also found underestimation of chronological age in Turkish boys and girls from 6 to 18 years old, although more evident in girls, concluding that the method was only accurate for boys.

More recently, Kirzioglu and Ceyhan [31] compared the Nolla and Demirjian methods with a sample of 425 Turkish children between 7 and 13 years old, from the same socio-economic class and the same ethnic group. An underestimation of −0.53 years was found for boys and −0.57 for girls with the Nolla method, this method being more accurate between 9 and 11 years in both sexes and in the group of 13-year-old girls. On the other hand, the Demirjian method overestimated boys’ age by +0.52 and girls’ age by + 0.75. Kirzioglu and Ceyhan [31] concluded that these methods are not totally suitable, with it being necessary to assess specific tables for this population.

Far from presenting consensual results, the research carried out led us to the need to test the applicability and credibility of the Nolla and Demirjian methods with a sample of the Portuguese and Spanish population. Substituting in the corresponding equation the Nolla [43] or Demirjan et al. [11] value, the resulting forecast is accurate, forming a useful instrument for diagnosis and treatment planning. The seven teeth considered by the Demirjian method were able to predict 47.5% of the chronological age of participants and the Nolla method predicted 64.4%. In our sample, therefore, the Nolla method was a more significant predictor.

The accuracy of both methods varied between the sexes and age groups. Both methods were found to be more precise with males. Estimation of chronological age for four age-groups defined from the cluster analysis showed that as the age-group increases, the predictive capacities of both methods diminish. The Nolla method was more accurate than the Demirjian method in early and late childhood for both sexes. Neither method could predict chronological age in adults. For girls, the Nolla method was more significant up to late childhood and the Demirjian method from this age up to 18 years old. Since the sex variable influenced the predictive capacities of both methods, we conclude that equations to estimate chronological age should use specific coefficients for males and females. Indeed, it is a fact that teeth appear in females before males [13, 25]. The dental maturity process also presents sex differences, and mineralization is also earlier in females than in males [13, 25, 37]. The earliest phases of dental maturity are very similar in both sexes up to the first onset of menstruation, greater development occurring beyond that period in girls [3].

We found the Demirjian method tends to overestimate the real age of participants and the Nolla method tends to underestimate it. Using Demirjian led systematically to overestimation of chronological age. Among others, overestimation was found in the studies by Frucht et al. [21], Willems et al. [50], Eid et al. [14], Foti et al. [20], Maber [38], Chen et al. [8], Galic et al. [22], Lee et al. [33], Nik-Hussein et al. [42], Lee et al. [34], Feijóo et al. [15, 16], Kirzioglu and Ceyhan [31], Flood et al. [18], Jayaraman et al. [29] and Djukic et al. [13]. Among the studies finding overestimation, we should mention those of Khorate et al. [30] with individuals in Goa, India, Sarkar et al. [46] with Indian individuals, Cruz-Ladeira et al. [10] with Venezuelan individuals and Chen et al. [8] with Chinese children. More recently, Jayaraman et al. [29] performed a meta-analysis of 274 studies where the Demirjian method was used. The authors recorded average overestimation of chronological age in all the studies (of 0.60 years for boys and 0.65 years for girls), except in a Chinese sample of boys and a Venezuelan one with boys and girls.

Few studies have investigated use of the Nolla method in different populations. One of the most recent studies was made by Kirzioglu and Ceyhan in 2012 [31]. The authors compared the methods of Nolla [43], Havikko [24] and Demirjian et al. [11] with a sample of healthy Turkish children between 7 and 13 years old, from the same socio-economic status and the same ethnic group. Underestimation of dental age was found with the Nolla method, being more accurate for chronological age between 9 and 11 years in both sexes and in the group of 13-year-old girls. Kirzioglu and Ceyhan [31] concluded that, despite the Nolla method being more accurate than those of Havikko and Demirjian, these three methods are not completely adjusted, it being necessary to define specific tables for that population. Bolanos et al. [4] used the Nolla method with a Spanish sample, finding high accuracy for boys and girls up to 10 years old, results which are in agreement with ours. Caro and Contreras [7] also found higher accuracy in the Nolla method than in the other methods they tested.

One of the possible explanations we point out for the Nolla method showing itself to be a more significant predictor may be related to the fact this method presents more inter-stage sub-divisions, allowing greater inter-stage differentiation of dental maturity. Another explanation could be because in the Demirjian method, the Second Premolar and the First Premolar were not significant in predicting participants’ chronological age and the Canine was a weak predictor. However, for the Nolla method, only the Lateral Incisor was not significant in predicting chronological age, all the other teeth being good predictors.

The exclusion of insignificant teeth increased the predictive capacity of the Demirjian method to 57.7% and that of Nolla to 74.5%. The better predictive capacities of Nolla compared to Demirjian is therefore demonstrated in a more heterogeneous sample regarding age (4–35 years), whether using the Nolla value [43] or the Demirjian et al. [11] global one, or when considering the specific influence of each tooth. Our results are in line with studies indicating the existence of inaccuracies in estimating chronological age, above all in the Demirjian method – Frucht et al. [21], Willems et al. [50], Eid et al. [14], Foti et al. [20], Maber [38], Chen et al. [8], Liversidge [36], Cruz-Ladeira et al. [10], Galic et al. [22], Lee et al. [33], Nik-Hussein et al. [42], Feijóo et al. [15, 16], Kirzioglu and Ceyhan [31], Flood et al. [18], Djukic et al. [13], Sarkar et al. [46], and Khorate et al. [30].

In all the studies which found significant differences between chronological age and dental age using the various methods, the authors have suggested using correction factors. According to Nik-Hussein et al. [42], the discrepancies between chronological age and dental age can be due to a positive secular general tendency in which growth and somatic development could contribute to earlier dental eruption and mineralization.

Our results agree with previous studies carried out in a variety of geographical locations, ethnic groups, nutritional and socio-economic conditions, which arrived at different results in relation to the original populations that gave rise to the methods, with the need to elaborate forecasting equations appropriate for each population [1, 32, 47].

We can estimate accurately the chronological age for early and late childhood using the Nolla and Demirjian et al. methods. Including adults leads to reducing the predictive capacities of both methods, and especially that of Demirjian.

The Nolla method showed greater predictive capacities than the Demirjian one in samples with more heterogeneous ages. The predictive capacity of both methods was significantly higher for boys and girls up to 10 years old, diminishing progressively up to 18 years old and ceasing to be significant beyond that age. Of all the age segments, the most favorable with the Demirjian method was up to 8 years old, and with the Nolla method it was up to 10 years, for both sexes. The Demirjian method tends to overestimate chronological age and the Nolla method tended to underestimate it, although the differences were less in relation to real age. It is therefore important to elaborate regression equations adapted to the populations studied.

Participants’ sex affected the magnitude of predictive capacities in both methods. The Nolla method was more accurate than the Demirjian method in early and late childhood for both sexes. For girls, the Nolla method was more significant up to late childhood and the Demirjian method from this age up to 18 years old compared to that of Nolla. It is therefore important to elaborate regression equations adapted to the populations studied, differentiating by sex and age-group.