Ethnic variations in dental maturity have been established and several investigators have expressed the need for ethnic specific standards for age estimation [15, 16]. This study has demonstrated that the southern Chinese reference data is the most accurate reference standard for estimating the age of children in Hong Kong. The accuracy can be attributed to the population specific reference standards; both the reference data and the study sample belong to the population group. The UK Caucasian and southern Chinese RDS were used to estimate the age of subjects in all of the age ranges. By contrast, only 60% of the subject’s ages were estimated using the Demirjian French-Canadian dataset. The maturation factors corresponding to the development of third molars were not included in the Demirjian analysis and hence it is impossible to perform age assessments for children above the age of 16 years . The subjects included in this study belonged to southern Chinese ethnicity and this information was obtained from the data in the well documented hospital files. The subjects’ ethnicity was further confirmed from the names of the subjects that were specific to southern Chinese ancestry. The subjects whose parents were from southern China were alone included in the study but any ethnic admixtures exceeding two generations could not be clearly verified.
Age difference (CA-DA) calculated from the methods employed in the current study demonstrated a specific pattern of distribution. The UK Caucasian RDS underestimated the age of male and female children below 5 years of age by one year. A minor difference was observed in the 6- to 16-year age range. Overestimation of the age of about 2.40 years was seen in the young adults aged 17 years and older. The French-Canadian dataset was able to estimate the age of most of the children within a range of one year; however, overestimation of age was observed in the adolescents. The southern Chinese reference dataset consistently estimated the age of children within one year of difference. Nevertheless, some variations were observed in female adolescents. The major differences in the estimated age were found in males and females aged 18 years and older.
Both UK Caucasian and the French-Canadian datasets were unable to estimate the age of southern Chinese subjects accurately hence necessitating to develop population specific reference data. This was eventually developed from 2306 subjects aged 2 to 25 years and validated for accuracy in the same age group. The overall difference between CA and DA from the validation study was 0.05 years for males and 0.03 years for females . The DPTs of subjects used in the earlier study were re-used in the current study for two reasons; firstly, to reconfirm the validity of the southern Chinese dataset and secondly, to identify differences in the estimated age using the same sample, but on three different datasets [9, 10]. In the current study, the difference between the CA and DA using southern Chinese dataset was − 0.02 years for both males and females and the difference was statistically insignificant proving that the dataset was more accurate than the UK Caucasian and French-Canadian datasets. This finding is consistent with the validation study [11, 17]. Although the total number of subjects included in the analysis was 266 with equal number of subjects in each age range (14 subjects in 19 age ranges), age could not be estimated for all subjects. The French-Canadian dataset does not include data for 3rd molars and hence could not be applied to estimate age of subjects over 16 years. Likewise, age of few subjects in the older age ranges could not be estimated due to difference in the timing of closure of root apices of third molars. For this reason, age could not be estimated for 12 subjects using the southern Chinese dataset and 14 subjects using the UK Caucasian dataset (Table 1).
The overall difference between CA and DA may be misleading at times since the extreme variations at certain age ranges may still produce result close to zero . Hence, it is imperative to report the findings using a scatter plot to demonstrate variations in the age at different age ranges. However, when confronted in legal scenarios, a question commonly raised is “how accurate is the method?”. To answer this, we have reported frequency data to indicate the percentage accuracy of the estimated age at different time intervals starting from 3 months to 30 months. Using the southern Chinese dataset, the age of 65% of the subjects could be estimated within a range of 6 months and 80% within 12 months. The remaining 18% subjects could be estimated within 24 months interval, sparing just 2% beyond 2 years. The results are in conjunction with a study that tested the application of UK Caucasian dataset on the UK subjects with 42% of age estimates within a range of 6 months and 68% of age estimates within a range of one year .
Most of the methods of dental age calculation that have been reported in the literature were based on staging the degree of dental development, or the measurement of the apices of the roots. These data are then used to construct a reference standard for age assessments [19, 20]. The French-Canadian method utilizes correspondence analysis of the data to each stage of tooth development. The overall maturity score is then compared to the chart values to establish the dental age. By contrast, the UK Caucasian dataset contains data values as mean age or average AoA for each tooth development stage. This is a simple and effective method to estimate dental age compared to Demirjian’s system that requires multiple calculations. In addition to the average AoA, UK Caucasian dataset also contains the standard deviation for each stage of dental development which in turn permits weighted age calculations to be performed. In the validation study on southern Chinese subjects, meta-analysis computation was employed to calculate the dental age, which takes into account different weightings, i.e., number, mean age, standard deviation and standard error in the analysis. In this study, we have used the simple average of the mean ages corresponding to each TDS . However, a study on multiple weighted average methods could provide us further information of the influence of weighting factors in age estimation for southern Chinese subjects.