Forensic age estimation based on magnetic resonance imaging of third molars: converting 2D staging into 3D staging

Abstract

Background: Established methods to stage development of third molars for forensic age estimation are based on the evaluation of radiographs, which show a 2D projection. It has not been investigated whether these methods require any adjustments in order to apply them to stage third molars on magnetic resonance imaging (MRI), which shows 3D information.

Aim: To prospectively study root stage assessment of third molars in age estimation using 3 Tesla MRI and to compare this with panoramic radiographs, in order to provide considerations for converting 2D staging into 3D staging and to determine the decisive root.

Subjects and methods: All third molars were evaluated in 52 healthy participants aged 14–26 years using MRI in three planes. Three staging methods were investigated by two observers. In sixteen of the participants, MRI findings were compared with findings on panoramic radiographs.

Results: Decisive roots were palatal in upper third molars and distal in lower third molars. Fifty-seven per cent of upper third molars were not assessable on the radiograph, while 96.9% were on MRI. Upper third molars were more difficult to evaluate on radiographs than on MRI (p < .001). Lower third molars were equally assessable on both imaging techniques (93.8% MRI, 98.4% radiograph), with no difference in level of difficulty (p = .375). Inter- and intra-observer agreement for evaluation was higher in MRI than in radiographs. In both imaging techniques lower third molars showed greater inter- and intra-observer agreement compared to upper third molars. MR images in the sagittal plane proved to be essential for staging.

Conclusion: In age estimation, 3T MRI of third molars could be valuable. Some considerations are, however, necessary to transfer known staging methods to this 3D technique.

Keywords:

• Third molar root
• panoramic radiograph
• surface head coil
• sub-adult

Acknowledgements

The authors wish to thank all the participants and everybody who helped with the recruitment. We are very grateful to Dr. Helen Liversidge for discussing stage assessment and comparing 2D with 3D images. Moreover, she provided invaluable language advice. We wish to thank the dentists who allowed us access to their patient records software in order to retrieve the panoramic radiographs. With special thanks to Rik Jamaels for enabling the gathering of these radiographs. We are pleased to acknowledge the organizational and administrative help given by Katrien Saegerman. Also the critical appraisal of the document by Inès Phlypo is appreciated. Finally we express our gratitude to Professor Dr. Marc Kunnen for his help with processing of the images in this paper. Results described in this manuscript were partly presented at the symposium on age estimation of the Society for the Study of Human Biology (SSHB) in association with the British Association for Biological Anthropology and Osteoarchaeology (BABAO) in Oxford, United Kingdom on 9–11 December 2014.

Disclosure statement

Funding for this research was entirely provided by the department of Radiology and Nuclear Medicine at Ghent University. The authors report no conflicts of interest.