Third molar development in a contemporary Danish 13–25 year old population
Introduction
When assessing the age in living individuals with an unknown or undocumented age, The Study Group on Forensic Age Diagnostics recommends a combination of: (1) physical examination; (2) radiological examination of the left hand and, if indicated, examination of the clavicles; and (3) radiological examination of the dentition. In most countries, the chronological age of 18 years marks the difference between being a minor or child as opposed to an adult [1].
For assessing age by the left hand bones, the atlas method by Greulich and Pyle (GP) [2] is the most widely used, although scoring methods by Tanner and Whitehouse (TW) [3] and Roche et al. (FELS) [4] probably also fulfil the demands of forensic practice. If bone maturation is completed, the GP method indicates an estimated chronological age of 19 years or above in males and 18 years or above in females.
The ossification of the medial clavicular epiphyseal cartilage can be assessed in both conventional radiographs and in Computed Tomography (CT) scans [5], [6], and the final developmental stage for both sexes appears to be reached when an individual is more than 20 years of age. The clavicle is thus a valid indicator for assessing whether an individual has passed the age of 18 years. Radiation dose may be an issue because of the proximity of major internal organs such as the thyroid; currently, studies are being carried out to assess whether magnetic resonance imaging can be used to assess the bones [7], [8].
This means that evaluation of the third molar, which is still developing in the late teens, will arguably continue to be the best available indicator for estimating chronological age around 18–20 years of age [9], [10]. Furthermore, several studies have described the development of the third molar [11], [12], [13], [14], [15], [16], and third molar development in different ethnic groups has been described at a global level [15], [17], [18], [19], [20], [21], [22], [23]. To our knowledge, no published articles have yet described the development of third molars in a Danish population and related this to chronological age. The evaluation of third molar mineralization is to a certain degree based upon a subjective assessment of stages of tooth development. High reproducibility is therefore crucial in minimizing observer bias inherent in the method [24]. The primary aim of this study was to describe the development of third molars within the age range 13–25 years in a contemporary Danish population, and hence to add to the existing body of data regarding global variation. The secondary aim was to assess inter- and intra-observer reproducibility of the scoring method.
Section snippets
Material
In this retrospective cross-sectional study, we assembled 1302 digital dental panoramic images (PANs), recorded during the years 2001–2015, of individuals between 13 and 25 years of age (633 males and 669 females) from their files at the Department of Dentistry and Oral Health, Section of Oral Radiology, Aarhus University, Denmark. There was no information available regarding ethnic origin in the patient files. The PANs were recorded for various diagnostic tasks. Half of the patients (51%) were
Methods
The assessment of third molar development was performed according to the method of Gleiser and Hunt (GH) [25], but with the modifications made by Kohler et al. [26]. With this method, third molar development is categorized into 10 developmental stages. Each stage corresponds to a particular developmental score, ranging from 1 to 10. For every PAN, each third molar present was given a score of 1–10, corresponding to the developmental stage. Examples of the scores in PANs are given in Fig. 1,
Inter- and intra-observer agreement
Of the 195 maxillary third molars included in the assessment, 19 were assessed as not eligible for scoring due to poor sharpness and contrast in the PAN, either by Observer 1, Observer 2, or by both, on either the first or second observation. These 19 scores were excluded from further analysis. None of the mandibular third molars were assessed as not eligible for scoring. Thus, the inter- and intra-observer analyses were based upon a total of 176 maxillary and 192 mandibular third molars, each
Discussion
Tooth formation is a continuous process and may be classified into stages. Different systems are available for classifying stages of tooth development. They differ with regard to number of stages and presentation and definition of each stage. While some classification systems are defined by changes in tooth and root form, e.g., the method developed by Demirjian et al. (DM) [9], other classification systems base stage definition on estimates of future root development, e.g., the method developed
Conclusions
Inter- and intra-observer variability analysis showed high reproducibility for the assessment of developmental third molar stages. We found that in when there was a difference in the developmental stages of the mandibular third molars roots, the mesial root was generally more advanced in development than was the distal root. There was no difference in the developmental stages between the left and right sides. In this study maxillary third molars were generally more advanced in developmental
Acknowledgements
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
We declare that there is no source of external funding, no disclaimers and no conflict of interest.
Part of the information has been presented as a poster at the triennial meeting of IOFOS (International Organisation of Forensic OdontoStomatology) in Leuven, Belgium September 13th–15th 2017.
References (46)
- et al.
Forensic age estimation from the clavicle using 1.0T MRI—preliminary results
Forensic Sci. Int.
(2014) - et al.
Third molar root development in relation to chronological age: a large sample sized retrospective study
Forensic Sci. Int.
(2003) - et al.
Die entwicklung des weisheitszahnes als kriterium der lebensaltersbestimmung
Ann. Anat.
(1994) - et al.
Studies on the progress of third-molar mineralisation in a Black African population
Homo
(2006) - et al.
Third molar development according to chronological age in populations from Spanish and Magrebian origin
Forensic Sci. Int.
(2008) - et al.
The chronology of third molar mineralization in the Austrian population—a contribution to forensic age estimation
Forensic Sci. Int.
(2007) - et al.
Demirjian’s stages and Cameriere’s third molar maturity index to estimate legal adult age in Peruvian population
Leg. Med. (Tokyo)
(2017) - et al.
Development of wisdom teeth as a criterion of age determination
Ann. Anat.
(1994) - et al.
Reproducibility of radiographic stage assessment of third molars
Forensic Sci. Int.
(2006) - et al.
Third molar root development in relation to chronological age: a large sample sized retrospective study
Forensic Sci. Int.
(2003)