Medical age estimation through evaluation of wisdom teeth on

panoramic radiographs, a literature study

Authors: Judith Ayele, Mona Sabet Motlagh

Tutor: Jan Ahlqvist (oral and maxillofacial radiologist)

Number of words in abstract: 250

Number of words in abstract and text: 3330

Number of tables and figures: 4

Number of references: 32

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ABSTRACT

Due to lack of identification documents or uncertainty in regard to past life stories

asylum-seeking individuals in Sweden are offered medical age estimation by The

Swedish Migration Agency to determine if the person is ≥18 years old. The age

estimation process consists of two examinations; panoramic examinations of the

lower wisdom teeth and magnetic resonance imaging (MR) of the thigh bone.

Dentists and medical radiologist assess the radiographs according to a probability

scale made by The Swedish National Board of Forensic Medicine and provide

separate age assessment that are used to determine whether or not the person of

interest is of legal age. The purpose of this review was to evaluate studies that have

analyzed wisdom teeth development in panoramic radiographs for medical age

estimations and assess if it is a reliable method. Searching the databases PubMed

and Web of Science identified included articles. The search resulted in 97 findings.

After abstract and full text review 25 studies were included. 13 studies present

mean age and standard deviation at different root development stages. Based on

this information the proportion of individuals <18 years old presenting fully and

not fully developed lower wisdom teeth was compiled. As a mean, a relative small

portion of individuals <18 years old presented fully developed roots, though with

large spread. Given there are few alternatives, using fully developed lower wisdom

teeth as an indicator of age ≥18 years is a reasonably reliable method due to a low

risk of assessing someone as adult when minor.

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INTRODUCTION

The number of asylum-seeking individuals in Sweden has increased during the last decade. The

majority of these people come from unprivileged and war-torn developing countries, such as

Syria and Iraq(Migrationsverket, statistics 2018). Due to lack of identification documents or

uncertainty in regards to past life stories The Swedish Migration Agency (“Migrationsverket”)

occasionally offer medical age estimation to individuals claiming to be minors (<18 years old in

Sweden. To determine if a person has reached legal age (≥18 years old), a combination of two

examinations are done- panoramic x-rays of the lower wisdom teeth which together with the

maxillary wisdom teeth are the only ones developing during this chronological period, and

magnetic resonance imaging (MR) of the thigh bone. After the radiographs have been analyzed

by dentists and medical radiologists, age estimation is done with the help of a probability scale

made by The Swedish National Board of Forensic Medicine (“Rättsmedicinalverket”). The

maturity estimation of the wisdom teeth is made by two different dentists who are independent of

one another, meaning that they are unaware of each other’s results. The dentists evaluate if

complete root closure has occurred in one of the lower wisdom teeth blindly, meaning they do not

have access to information regarding the person of interest (such as ethnicity, age, gender etc.). If

the radiograph is not possible to evaluate according to the probability scale due to poor x-ray

quality or missing lower wisdom teeth, the individual is considered to be “not assessible”. If both

dentists consider the individual to be “not accessible” the MR will by itself compose the

foundation of the age estimation, and the same applies for situations when the thigh-bone cannot

be evaluated. However, if only one of the dentists consider the radiograph to be “not assessible” a

third party, consisting of a forensic odontologist at The Swedish National Board of Forensic

Medicine, will make the final decision. When the thigh bone is examined with MR the growth

zone of its lower part is assessed to evaluate if complete maturity has occurred, meaning that the

person of interest is ≥18 years old. The same process applies here, regarding the evaluation being

performed blinded, the assessors being independent of each other and a third party, a medical

radiologist, assessing the radiograph when one party considers it to be “not assessible”. In order

for the final age estimation to state that the person of interest is ≥18 years old, the maturity-scale

for both the wisdom teeth and lower thigh bone have to be evaluated as completely matured. In

cases where there are disagreements between the assessing doctors and dentists the person of

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interest is estimated to be a minor. (Phone contact with The Swedish Migration Agency

Migrationsverket, Asylum department. 2017-10-11).

There are several ways to evaluate the development of wisdom teeth. The most common method

is mineralization classification according the Demirjian´s system. This method is based on the

development of the wisdom tooth being divided into eight stages. The second last stage, G-stage,

is defined as; ”The walls of the root canal being parallel and its apical end still partially open”.

The final stage, H-stage is defined as ”The apical end of the root canal being completely closed

and the periodontal membrane having a uniform width around the root and the

apex”.(Metodbeskrivning för Rättsmedicinalverkets medicinska åldersbedömningar, 2017).

The purpose of this systematic review was to establish if medical age estimation through

analyzing wisdom teeth development with panoramic radiographs is a reliable method. This is of

importance in order to minimize mainly the group of individuals that are wrongly classified as

adults when minors, but also adults that are assessed as minors since it can have negative

consequences in an individual's life.

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MATERIALS AND METHODS

The protocol for this review was the PRISMA 2009 checklist (available at www.prisma-

statement.org).

Relevant keywords were chosen in order to search for articles regarding medical age estimation

using panoramic radiographs in different databases. The following three combinations of words

were used;

1. age estimation, lower third molar, panoramic radiographs

2. third molar development, chronological age, panoramic radiography

3. radiography panoramic, root development, age estimation, lower third molar

Articles were identified by searching the databases PubMed and Web of Science, last searched

September 2017 and December 2017. Duplicates were excluded and each author analyzed the

remaining articles separately by reading the abstracts to determine if they fulfilled the criteria to

be included in the systematic review. The study selection processes is presented in a flow

diagram (Figure 1). Database searching showed 97 findings. After abstract and full text review 25

studies were included. Included studies needed to present the age of individuals with complete

root-closure of third molars on panoramic radiographs, separate results for females and males as

well as an appropriate age span (around legal age). When there was any uncertainty regarding

which articles should be excluded, the two authors discussed the content in order to reach a

mutual agreement. Publications were excluded due to reasons such as foreign language other than

English and Swedish, inappropriate age spans, use of other x-rays than panoramic radiographs

and age evaluations where root mineralization was not assessed. Remaining eligible articles were

assessed thoroughly by both authors, and those fulfilling the desired criteria were accommodated.

The 23 included studies are presented in table 1, featuring study characteristics, results of

individual studies and additional analysis with the use of an evidence-based method for reporting

systematic reviews called Preferred Reporting Items for Systematic Reviews and Meta- Analyses

(PRISMA). In cases where calculations were needed, for instance when mean age was not

presented but sufficient information was provided in the study, it was calculated individually by

each author and finally recalculated together to minimize the risk of error. 13 of the included

studies present mean age and standard deviation at different root development stages and was

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used to calculate the proportion of an individual being over/under 18 years of age through a

binomial distribution formula, results are presented in table 2. Normal distribution curves for the

G- and H-stage at different chronological ages, illustrating the information in table 2, was

constructed through Microsoft Excel and presented in figure 2. Mean values for the proportion of

individuals <18 years of age presenting H-stage in relation to the overall number of people under

legal age in both stages, for men and women were calculated from the available data to get an

idea of how often H-stage appears in minors.

Information regarding medical age estimation performed in Sweden was obtained through

personal telephone communication with The Swedish Migration Agency and through a document

presenting the process that was provided by Ann Lemne, development- and project manager at

The Swedish National Board of Forensic Medicine.

Ethical considerations: The Ethics Forum at the Department of Odontology, in Umeå, Sweden,

made an ethical evaluation of the planned study. Approval to execute the systematic review was

received on 9th of May 2017. The Ethics Forum concluded; “appropriate ethics considerations

have been integrated into this degree project”.

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RESULTS

Table 1 presents the 25 included studies in this systematic review. Relevant characteristics such

as the number of female and male participants, their ethnicity along with age span, number of

observers evaluating radiographs, region of interest, exclusion- and inclusion criteria, additional

analysis as well as represented ages when in G- respectively H-stage is featured in the table. 13 of

the included studies do not state the number of participating observers nor if all radiographs have

been examined by the mentioned assessors. Eight of these articles do not mention exclusion

criteria and a total of 14 articles do not incorporate inclusion criteria. 17 studies use both the

upper and the lower wisdom teeth to evaluate the root development.

Table 2 demonstrates calculations of the proportions of individuals being <18 years of age and

presenting the G-stage or the H-stage for men and women. The calculations are based on the 13

studies that present mean age and standard deviation for ages in the G- and H-stage. In reality the

numerical values presented for stage H illustrates the distribution of participants in the study

rather than different ages it occurs in, as for the G-stage, this is due to it being a final and

permanent stage in root development. Table 2 also presents mean values for the proportion of

individuals <18 years of age presenting H-stage in relation to the overall number of people under

legal age in both stages. The size of these proportion varies largely between the different studies,

with a mean of 12,1% (Max 33,1 %, min 1,0%) for men and 8,7 % (Max 18,3 %, min 0,3%) for

women.

Figure 2 demonstrates normal distribution curves based on mean and standard deviations for ages

in the G- and H-stage presented in the same 13 studies as in table 2. The 18-year threshold is

marked with a vertical line. Diagrams for male and females are presented separately.

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DISCUSSION

The accuracy of a diagnostic test has two aspects to it, sensitivity and specificity. Sensitivity in

this case is rather low since a relative large amount of people with open apices are older than 18

years. Specificity is in this case defined by the proportion who demonstrate open apices (G-stage)

when <18 years of age. A high specificity implies a low number of false positive results, in this

case meaning that the diagnostic test rarely assess someone to be adult when being minor. Both

sensitivity and specificity depend on the cut of value, which in this case is; whether or not root

closure has occurred(Demirjian. A, 1973). Root closure can be regarded as a high cut of value,

leading to high specificity. From a tests sensitivity and specificity, positive and negative

predictive values can be determined. In this case positive predictive value is the probability that a

person presenting complete root closure on x-rays is ≥18 years of age. Based on the analyzed

studies the method has a high positive predictive value. Positive predictive value is, however,

highly dependent on the prevalence which is unknown when performing age estimation.

A problem with assessing age based on root closure (H-stage) is that it has happened prior to the

x-ray being taken. Another important fact is that the H-stage is not transitional but permanent.

The age span of the H-stage is in other words “open” e.g. with increasing age, the root apex will

remain closed. Therefore the relation between the periods in time at which the H-stage starts to

appear in relation to the G-stage (and stages before) is important for a reasonable correct

determination of a person being ≥ 18 year of age. Root closure seems to occur around late

teens/early twenties. The time for root closure is presumably normal distributed. Radiographic

examinations do, however, not reveal when root closure happens but if closure exists or not.

Therefore the H-stage cannot be described by a Gaussian curve. In 13 studies figures for mean

values and standard deviations for the H-stadium are presented and were used in this study to

perform the calculations in table 2 and illustrations in figure 2. The mean values and standard

deviations for the H-stage are, however, based on the age at which apex appeared closed in the x-

ray images and not when the apices closed. An inclusion criterion for the studies in this review

was that the participants should be in the age span around legal age. Therefore the illustrations in

Figure 2 show the supposed distribution of the age span and composition of the study materials

rather than when apices close. The calculations in table 2 are performed with that presumption

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and uses the Gaussian curves to estimate the proportion of persons being <18 years of age

presenting the H-stage. This approach is not adequate since the number of persons in different

age groups varies and the calculated figures should in no way be regarded as reliable. The fact

that there are people also presenting the F-stage just below the 18-year limit should e.g. also be

addressed in order to avoid overestimating the proportion of persons presenting the H-stage. The

calculations do, however, indicate that the proportion of people <18 years of age presenting the

H-stage is relative small. The opposite problem that the participants would be determined

younger than their actual age when presenting stage G is much larger as seen by the proportion of

persons above the 18-year limit presenting the G-stage.

Ethnicity is often included as a component in the discussions in the various studies. According to

English Oxford Living Dictionaries, ethnicity is defined as the fact or state of belonging to a

social group that has a common national or cultural tradition(Beth Dawson-Saunders, Robert G.

Trapp, 1994). Since ethnicity does not have to be biologically linked and is not defined by any

evident criteria it can be very difficult to establish what ethnicity a person belongs to. An

individual's ethnicity can vary depending on self-identity and one's own interpretation of the

word. In some cases, a person can even be considered to have multiple ethnicities. Uncertainty

revolving around the definition of the word makes it difficult to distinguish ethnical attributes in

regard to root development. In addition, the obtained material in this systematic review is not

sufficient to assess any sort of ethnical differences.

Variations in root development between sexes were noticed in all included studies. In general

females reach the G-stage later than men, ranging from a couple of months up to a year for most

wisdom teeth. In some articles this phase occurred simultaneously between the sexes or some

months earlier in men. Females present an overall higher age at the G-stage. However, the gender

variations cannot be related to specific teeth but rather illustrate a random variation, therefore no

conclusion can be made regarding gender differences for specific teeth. Age difference between

sexes after root closure has occurred is similar to those seen at the G-stage. As mentioned

previously it is self-evident that root closure has occurred prior to the day of the H-stage

evaluated x-ray was taken which can make the results misleading.

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Possible sources of error in this review are insufficient information provided in the reviewed

articles and/or inaccurate calculations made by the authors of this article. 13 of the 23 included

studies do not state the number of participating observers nor if all radiographs have been

examined by the mentioned assessors and, if so, what happened when disagreements occurred

between different observers regarding root development stages. Another piece of information that

is missing in several of the studies are inclusion/exclusion criteria that can affect the obtained

result in a negative way, like local pathology, systemic disease or genetically linked syndromes

that can influence the development of wisdom teeth. The manually calculations made by the

authors could also be a source of error due to human factors. The same applies to interpretation

and conversion of numerical results. All of these potential errors could have contributed to

inaccuracies in the obtained outcome. However, these possible sources of error are not considered

to be of great importance in the overall result.

When it comes to age estimation by accessing root development there is, always a risk that a

child is mistaken for an adult (≥ 18 years old), which is an ethical dilemma. According to The

Swedish Migrations Agency (information obtained through telephone communication)

individuals who claims to be minors but are later assessed as adults through radiographic

evaluation will not be given a specific age, but rather classified as an adult (≥ 18 years old)

regardless of the alleged age, that will be kept. The consequence of being assessed as an adult

when minor is being deprived of rights such as going to school, free health- and dental care or

receiving a guardian when asylum seeking unaccompanied by adults, which is of national law in

Sweden as well as a part of the United Nations Convention on the Rights of the Child. Several of

the reviewed articles demonstrate individuals with complete root closure of wisdom teeth under

the age of 18, which according to the evaluation criteria submitted by The Swedish Migrations

Agency would lead to a minor wrongly being assessed as an adult. Even though it is possible for

a teenager to be mistakenly classified as an adult it is important to take into consideration that the

age estimation processes is performed only when there is uncertainty in regards to adultness.

Therefore, someone with a clear childlike appearance will most likely not be perceived as an

adult in the first place. The main problem revolves around differentiating individuals that has

entered puberty and exhibit masculine/womanly features such as facial hair, deep voices and

adult like physique from actual adults when root closure has occurred. There is also a risk that an

adult is assessed as a minor, also known as a false-negative, even though this is not considered as

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big issue due to the consequences not being as severe and the cut off value reducing the

probability of this occurring. Wrongly being classified as < 18 years old causes temporary

repercussions such as being deprived of the right to obtain a driver's license, buy alcoholic

beverages, laws and regulations regarding prison sentences and voting in general elections.

The purpose of this study was to determine if age estimation through assessing root development

on wisdom teeth is a reliable method in order to evaluate if a person is of legal age or not. After

reviewing relevant articles concerning this topic it is clear that the age when root closure has

occurred vary between different studies, whereof several exhibit minors when complete apex root

closure has occurred. Since it is not possible to determine if any of the included articles are

trustworthier than others, all of them contribute equally. This in turn brings up the question

regarding the definition of reliability, which in many cases is a question of interpretation. In

short, according to The English Oxford Living Dictionaries the definition of reliability is “quality

dimension of a system that reflects its ability to function satisfactorily with minimum

disturbance, errors and repairs”. According to the findings in this systematic review, age

estimation through assessing root development can, based on the relative small proportion of

people presenting H-stadium at an age < 18, and given there are few or no alternatives, be

regarded as a reasonable satisfactorily reliable method.

ACKNOWLEDGMENT

We would like to express our gratitude to our supervisor and dental radiologist Jan Ahlqvist for

mentoring and supporting us through this project.

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Figure 1, demonstrating the study selection process through a PRISMA flowdiagram.

Table 1, presenting the 23 included studies in the systematic review and their characteristics.

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Table 2, presenting the probability of an individual being <18 years of age before and after root closure.

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Figure 2, normal distribution curves created from mean values and standard deviations presented in 13 papers, demonstrating the

probability for different ages when presenting tooth development in G- and H-stage.

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