Magnetic resonance imaging of third molars in forensic age estimation: comparison of the Ghent and Graz protocols focusing on apical closure
To compare the Ghent and Graz magnetic resonance imaging (MRI) protocols for third molars, focusing on the assessment of apical closure. To study the influence of (1) voxel size and (2) head fixation using a bite bar. To compare both protocols with a ground truth of apical development.
Materials and methods
In 11 healthy volunteers, 3T MRI was conducted, including four Ghent sequences and two Graz sequences, with and without bite bar. After removal, 39 third molars were scanned with 7T μMRI and μCT to establish the ground truth of apical development. Three observers in consensus evaluated assessability and allocated developmental stages.
The Ghent T2 FSE sequence (0.33 × 0.33 × 2 mm3) was more assessable than the Graz T1 3D FSE sequence (0.59 × 0.59 × 1 mm3). Comparing assessability in both sequences with bite bar rendered P = 0.02, whereas comparing those without bite bar rendered P < 0.001. Within the same sequence, the bite bar increased assessability, with P = 0.03 for the Ghent T2 FSE and P = 0.07 for the Graz T1 3D FSE. Considering μCT as ground truth for staging, allocated stages on MRI were most frequently equal or higher. Among in vivo protocols, the allocated stages did not differ significantly.
Imaging modality-specific and MRI sequence-specific reference data are needed in age estimation. A higher in-plane resolution and a bite bar increase assessability of apical closure, whereas they do not affect stage allocation of assessable apices.
KeywordsAge determination by teeth Third molar Adolescent Adult Magnetic resonance imaging
Intra-class correlation coefficient
Micro computed tomography
Micro magnetic resonance imaging
Constructive interference in steady state
Fast spin echo
Specific absorption rate
Zero echo time
We are very grateful to all participants and everybody who helped with recruitment. We wish to express our most sincere gratitude and appreciation to Martin Urschler for making the exact parameters of the Graz protocol available for our research and for his critical appraisal of the manuscript. We also want to thank Dominique Neyts for her critical review of the manuscript. Lastly, we gratefully acknowledge the contribution of Geert Dermout and Louis Simoen in the production of the figures.
This study has received funding by the American Society of Forensic Odontology (ASFO) in form of its Research Grant 2017.
Compliance with ethical standards
This project was approved by the Ghent University Hospital Ethics Committee.Written informed consent was obtained from all volunteers, and in case of minors, from their parents.
Conflict of interest
Sara Neyt declares a relationship with the following company: MOLECUBES NV (Gent, Belgium). The μCT scans for the current study were performed free of charge by this company.
The other authors of this manuscript declare no relationships with any companies, whose products or services may be related to the subject matter of the article.
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