Third molar MRI in Forensic Age Estimation: protocol Development and considerations for use

Established dental age estimation methods in sub-adults mainly study the development of third molar root apices on radiographs.1,2 In living individuals, however, avoiding ionizing radiation is expedient. Studying dental development with magnetic resonance imaging (MRI) complies with this requirement, adding the advantage of imaging in three dimensions. Several studies investigated the use of MRI for dental age estimation.3-5 However, none of these studies discussed the differences between staging on radiographs and on MRI. Firstly, this study aims to elaborate the development of a 3 Tesla MRI protocol to visualize all third molar positions for forensic age estimation. Particular attention will be given to the development of the third molar root apices.6 Secondly, this study aims to prospectively study root stage assessment of third molars using MRI. In order to provide considerations for 2D staging into 3D staging, MRI will be compared with panoramic radiographs.7 To develop a clinically feasible MRI protocol visualizing all third molars for age estimation, ex vivo scans of porcine jaws and in vivo scans of ten volunteers aged 17-25 years were performed. Studied parameters were T1 versus T2 weighting, ultrashort echo time (UTE), fat suppression, in plane resolution, slice thickness, 3D imaging, signal-to-noise ratio, and acquisition time. A bilateral four-channel flexible surface coil was used. Two observers evaluated the suitability of the images. To compare third molar staging on MRI with staging on panoramic radiographs, all third molars were evaluated in 16 participants aged between 14 and 26 years. Three staging techniques were studied by two observers.8-10 T2-weighted images were preferred to T1-weighted images. To clearly distinguish root apices in (almost) fully developed third molars an in plane resolution of 0.33 x 0.33 mm² was deemed necessary. Taking acquisition time limits into account, only a T2 FSE sequence with slice thickness of 2mm generated images with sufficient resolution and contrast. UTE, thinner slice T2 FSE and T2 3D FSE sequences could not generate the desired resolution within 6.5 minutes. Lower third molars were equally assessable on both imaging techniques (93.8% MRI, 98.4% radiograph). Upper third molars were more difficult to evaluate on radiographs than on MRI (96.9% MRI, 43% radiograph). Inter- and intra-observer agreement for staging was higher in MRI than in radiographs. In both imaging techniques lower third molar staging showed higher inter- and intra observer agreement compared to upper third molar staging. MR images in the sagittal plane proved to be essential for third molar staging. Most decisive roots were the palatal in upper third molars and the distal in lower third molars. Three Tesla MRI of the third molars is a feasible technique for age estimation, in which a T2 FSE sequence can provide the desired in plane resolution within a clinically acceptable Proposal Id: 170949 Short Title: Third Molar MRI in Forensic Age Estimation [For Reference Purposes acquisition time. Several considerations are necessary to transfer known radiographical 2D staging methods to this 3D MRI application.status: publishe