Dental age estimation: development and testing of a reference data set for Qatari children, adolescents, and young adults aged between 5 and 25 years

The purpose of this study is to establish and test a reference data set of dental development of Qatari subjects aged between 5 and 25 years. Radiographs of individuals aged between 5 and 25 years were re-used to establish a reference data set (RDS). A scheme comprising 8 tooth development stages (TDS) was used to assess all the teeth on the left side of the maxilla and mandible. The accuracy of dental age estimation (DAE) was tested with a separate sample of radiographs – the validation sample (VS) comprised 50 females and 50 males of known chronological age (CA). Dental panoramic tomographs (DPT) of 1,597 Qataris were assessed. The summary data for the individual TDS comprising the number (n-tds), mean (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{\mathrm{x} }$$\end{document}x¯-tds), standard deviation (sd-tds), 0th%-ile (the minimum), 25th%-ile, 50th%-ile (the median), 75th%-ile, and 100th%-ile (the maximum) were used to estimate the age of the VS subjects using the simple average method (SAM). There is a significant difference in dental age of 4.8 months in the female group when compared to the CA. The difference in the male group is 4.5 months. This shows similar differences to assessments of other ancestral or ethnic groups.


Introduction
There has been a significant increase in illegal migration during the last 20 years.Many migrants do not have identification documents or a record of their date of birth.Age estimation (AE) is important for legal, social, forensic, and archaeological purposes.
Dental age estimation offers a biological state that mimics chronological age thus enabling the following: 1. Estimation of the chronological age (CA) of an individual with unknown date of birth or missing identification documents.In addition to the point estimate of age, it is important to indicate the uncertainty associated with the estimate.Age estimation of these individuals is necessary to establish eligibility for civil rights, education, or social benefits.

A further need for AE is in criminal proceedings
where the judicial process is determined by the age of the accused.3. To provide reference standards for different ethnic, ancestral, racial, and identifiable human groups.
The United Nations Convention on the Rights of the Child (UNCRC 1989) [1] is a widely recognised international treaty that has changed and improved the way children are perceived across the globe.Young people aged less than 18 years are cared for under regulations pertaining to minors.There are large numbers of refugees of uncertain age who do not have birth records.Age estimation is necessary to ensure that social care, healthcare, and education are appropriately provided.There is also a safeguarding issue because adult asylum seekers who are over 18 years but claiming to be under 18 years of age should not be domiciled in the same accommodation as minors.DAE may assist in cases of child trafficking.Underage girls have been forced into marriage, and in these cases, traffickers claim that the children are older than they appear.
Age estimation may be important in criminal proceedings as some criminals, to avoid being punished as adults, claim to be younger than they look.This is so these young adults serve a sentence under the juvenile penal code.In Qatar, the age of criminal responsibility for children is between 7 and 17 years of age.This is stipulated by the Supreme Judiciary Council in Qatar.
There have been many attempts to devise schemes to estimate the age of children [2,3] In a paper published in 1973 [2] it was stated that " … it should be remembered that the sample on which they are based is of entirely French-Canadian origin.The dental maturity scores for a given chronological age may well be greater or less in other populations …" This is an important and often overlooked statement.
The purpose of this study is to use extant dental panoramic tomographs (DPT) to prepare a reference data set (RDS) for Qatari children, adolescents, and young adults to create an ethnic-specific dataset to enable assessment of dental maturity in Qatari subjects and from this to estimate dental age (DA) with the associated range of uncertainty.

Reference data set
The RDS comprised 1600 DPTs of female and male Qatari children, adolescents, and young adults.The DPTs were retrieved from the radiological archives of Rumailah Hospital and Al-Wakra Hospital outpatient departments as well as an orthodontic office.The chronological age of each subject was calculated using the date of birth and the date of radiographic exposure of the DPT.Digital copies of the DPTs were transferred from Qatar using a portable password protected storage device.This was to ensure and protect anonymity.

Exclusion criteria
• Non-Qatari subjects • Poor quality DPTs • Subjects with a medical condition that may affect dental maturation

Tooth development stages
These were assessed using the 8 stage system described by Demirjian, Goldstein, and Tanner in 1973 (Fig. 1 and Table 1) [2].The date of birth and sex was blinded from the assessor at the time of the assessment.The TDS were recorded on a specially designed form and then entered into a Microsoft Access database.The assessment included all the teeth on the left side of both the maxilla and mandible.Teeth that were fully developed (stage H) were recorded but excluded from calculations for DAE (Fig. 2).

Observer agreement
The primary investigator (NAO) recorded the TDSs on the left side of 10 DPTs, comprising 160 assessments.These DPTs were separate from the main study.The assessments were on 2 occasions 2 weeks apart to determine within observer agreement (WOA).A second observer (VSL) assessed the same DPTs to determine between observer agreement (BOA).Both the WOA and the BOA were calculated using Cohen's kappa [4], and the outcome index was assessed according to the categories suggested by Landis and Koch in 1977 [5].

Data processing
The major part of the study was to establish a RDS for the young Qatari population.The TDSs (A through H) of each tooth present on a sample radiograph were entered into a Microsoft Access database.To extract data from the database, queries were created which included the following information: ID number, ethnicity, sex, and age at assessment (AaA) of each TDS.
These queries were exported to Excel and a small worksheet was created for each TDS for both females and males, for example, UL8Gf [Upper Left Third molar, Stage G, female].Each of these queries comprised the dataset for that specific stage from which the number (n-tds), the mean ( x − tds ), standard deviation (sd-tds), 0th%-ile (minimum), 25th%-ile, 50th%-ile (median), 75th%-ile, and the 100th%ile (maximum) were calculated.

Validation study
The second part of this work was to assess the accuracy of the method of DAE when utilizing the Qatari RDS.The 1 3 Fig. 1 The 8 stages of dental development described by the Anglo-Canadian research team.These descriptions should be used when viewing dental panoramic tomographs to determine the stage of development from A to H validation sample (VS) comprised 100 DPTs of Qatari children and adolescents.There were 50 females and 50 males with known date of birth and date of radiographic exposure.These data were blinded from the assessor.The radiographs were separate from the RDS.The TDS from each tooth on the left side was entered into an Excel worksheet which semi-automatically looked up the n-tds, x − tds, and sd − tds , from the RDS to calculate the DA to enable comparison of the CA with the DA for each VS subject [6].When the 50 female and 50 male subjects had been assessed, CA and DA were compared using Student's t test.

A
In both uniradicular and multiradicular teeth, a beginning of calcification is seen at the superior level of the crypt in the form of an inverted cone or cones.There is no fusion of these calcified points B Fusion of the calcified points forms one or several cusps, which unite to give a regularly outlined occlusal surface C a. Enamel formation is complete at the occlusal surface.Its extension and convergence toward the cervical region is seen b.The beginning of a dentine deposit is seen c.The outline of the pulp shape has a curved shape at the occlusal border The distribution of individual TDS for subject 47f, gives the estimated DA with the variation of the individual TDS (Fig. 3).In addition to this formal statistical test, Bland-Altman graphs were used to show the variation of the difference between CA and DA around the line of no difference (Figs. 4 and 5) [7].

Sample distribution
The number of female and male subjects by 1 year age bands is shown in Table 2.

Observer agreement
The WOA score for TDS was 0.9203 and the BOA score for TDS was 0.8401 demonstrating an almost perfect agreement [5].

Reference data set
Radiographs of 1597 Qatari children, adolescents, and young adults age between 5 and 25 years were assessed by the main investigator (NAO) to create the RDS.The data for females and males across the whole range of the age are shown in Table 3 comprising normal distribution summary statistics and percentile distribution summary statistics.

Worked example
The detailed procedure for the computer-assisted procedure to estimate individual DA is detailed in a paper published in 2018 [6].

Validation study
The data extracted for each subject are illustrated in the worked example (Table 4).The VS of 100 subjects comprise 50 females and 50 males age between 5 and 25 years with known date of birth and date of radiographic exposure.The results from the calculations for the whole of the VS are shown separately for females (Fig. 4) and males (Fig. 5).
The mean CA for females was 10.8 years, sd 1.74 years, the lower confidence limit was 10.31 years, and the upper confidence limit was 11.29 years.
The mean difference between CA and estimated DA is 0.40 years or an overestimate of 4.84 months (Table 5).
The mean CA for males was 10.89 years, sd 1.82 years, the lower confidence limit was 10.37 years, and the upper confidence limit was 11.41 years.
The mean difference between CA and DA for males is an overestimate of 0.38 years or 4.55 months (Table 6).

Bland-Altman graphs
These graphs [7] explore the agreement between CA and DA for both female and male subjects.The graphs (Figs. 4  and 5) demonstrate the difference between the CA and DA within the female and male VS groups.The horizontal dotted line is located at the mean difference between the CA and DA whilst the continuous line represents the "no difference" value between CA and DA.In both the female and male groups, the mean difference was statistically significant.

Discussion
The aim of DAE is to estimate the chronological age of an individual with unknown date of birth.It may be used for clinical, legal, civil, criminal, and forensic purposes.An important consideration is the error of the method.The preferred term is the uncertainty associated with the estimate.This is easily and reliably achieved using Draft Quicksheets [6].
In the present study, only the tooth development stages, which comprise the first part of the Demirjian, Goldstein, and Tanner method [2], were employed.This is because the mathematical procedures leading to the maturity score cannot be unravelled [8].In the SAM procedure, all the developing teeth on the left side including third molars were used.This has increased the number of assessed teeth and therefore likely to lead to an improvement in the accuracy or reliability of the estimated age as it uses the maximum information available.This is born out to a considerable extent by the relatively small CA minus DA differences shown in the results of the validation study.In addition, the inclusion of third molars up to and including stage G makes the method suitable for older subjects aged 16 years or more.Stage H is not used as it is unbounded in its upper border for each tooth.This will be the subject of a further communication because the age of apex closure cannot be identified without censoring [8].Also, the mean value for stage H cannot be used in simple mathematical procedures such as averaging the AaA of TDSs present in a subject.Therefore stage H is excluded from any calculations in SAM.
Each ethnicity or ancestral group has its own characteristics including with DAE.Many studies investigate the validity of using the French-Canadian standards on other populations [9][10][11].However, it was found that  age at attainment is the term often used in DAE research reports.This is logically inconsistent as the age at which a stage has been attained cannot be ascertained from a single "snapshot" radiograph of developing teeth.Age at assessment (AaA) is the logical and better understood term.
The data collection was limited to Qatari subjects and partitioned by sex.The large number of DPTs results in a sufficiently large number in each 1 year age span and consequently for the individual TDS to ensure a narrow range of the CI of the differences between females and males.In practice, over 73% of the AaA values for the individual TDS were earlier in females.This emphasizes the importance of sex-specific data in addition to the need for ethnic specific data.

Conclusion
A reference data set for the mean age at assessment of the different TDS for the Qatari population has been established.The average difference between CA and DA for female and male subjects was 4.8 months and 4.5 months, respectively.

Fig. 2
Fig. 2 DPT for subject ID 47 female showing the TDS assessed for this subject.Teeth on the left side only are used.The tooth development stages are indicated in the upper case type on the image

Fig. 3
Fig. 3 Forest plot showing the variation around the median value for DA using the 25th to 50th percentiles

Table 1
Written guide of morphologically related descriptions of Demirjian's TDS

Table 2
Numbers of subjects contributing radiographs by 1 year age spans A total of 1,597 subjects spread fairly evenly between females and males comprised the DPT from subjects resident in Qatar

Table 4
Worked example.Data extracted for subject 47.The Demirjian TDS are indicated as B, E, F, G, H.The data for these stages are extracted from the RDS (Table 3).AaA, age at assessment Dental age = 9.61 years; sd = 0.98; chronological age = 10.41 years Bland-Altman plot demonstrating that the spread of DA values is evenly distributed around the mean value of the CA (for females) 2. Training and careful management of the WOA and BOA supports the use of the 8 stage TDS system.3. A validation set was used to test the accuracy of the RDS when used to estimate the dental age of Qatari children, adolescents, and young adults.
1.A large reference data set has been established for Qatari subjects.2. There is a clear difference between Age at Assessment for females and males as regards Tooth Development Stages. 3. The Simple Average Method provides age estimation within 5 months of the Chronological Age.