Abstract— The dentine-enamel junction (DEJ) is an important internal interface with strong and durable bonding between the hard outer layer (enamel) and the soft inner tooth core (dentine). This study investigated the microstructure of the DEJ by X-ray imaging method and synchrotron X-ray scattering techniques. Further high resolution elastic modulus mapping indicates that the DEJ is a band with a graded mechanical property rather than a discrete interface. The microstructure-property relationship is also illustrated. The knowledge of the architecture and properties of the natural DEJ will help in the biomimetic development of dental restorations and novel replacement materials and application techniques. Index Terms—dentine-enamel junction, mechanical property, synchrotron X-ray scattering, microscopy I. INTRODUCTION OR many decades now, the continued demand for improved dental treatment and prosthetics has driven the advancement of understanding of the micro-architecture of human teeth. The dentine-enamel junction (DEJ) is an important internal interface between the highly mineralized hard outer layer (enamel) and the softer tooth core (dentine). Unless diseased, this interface never fails by fracture or collapse, despite the extreme thermo-mechanical loading it Manuscript received April 8 th , 2014; revised April 11 th , 2014. This work was supported in part by UK EPSRC through grants EP/I020691 “Multi - disciplinary Centre for In-situ Processing Studies (CIPS)”, EP/G004676 “Micromechanical Modelling and Experimentation”, and EP/H003215 “New Dimensions of Engineering Science at Large Facilities”. Diamond Light Source is acknowledged for providing the beam time. Tan Sui is doctoral student in the Department of Engineering Science, University of Oxford, OX1 3PJ, UK (e-mail: tan.sui@eng.ox.ac.uk). Tao Li is postdoctoral research assistant in the Department of Mechanical Engineering, National University of Singapore, Singapore, 117576 (e-mail: peach.fish.b@gmail.com) Michael A. Sandholzer is doctoral student at the School of Dentistry, University of Birmingham, B4 6NN, UK, (e-mail: MXS142@bham.ac.uk). Eric Le Bourhis is Professor of Institut P’,CNRS UPR 3346, University of Poitiers, SP2MI, BP 30179, F86962 Futuroscope Chasseneuil Cedex, France (e-mail: eric.le.bourhis@univ-poitiers.fr). Kaiyang Zneg is Associate Professor of the Department of Mechanical Engineering, National University of Singapore, Singapore, 117576 (e-mail: mpezk@nus.edu.sg) Gabriel Landini is Professor of Analytical Pathology at the School of Dentistry, University of Birmingham, UK, B4 6NN (e-mail: G.Landini@bham.ac.uk ). * Alexander M. Korsunsky is Professor of the Department of Engineering Science at the University of Oxford, OX1 3PJ, UK (corresponding author, tel: +44-18652-73043; fax: +44-18652-73010; (e-mail: alexander.korsunsky@eng.ox.ac.uk). experiences in the oral cavity. This stands in stark contrast to the interfaces between artificial dental restorative materials (fillings) and dentine [1]. The DEJ thus constitutes a superb lesson from nature on how to achieve strong, durable bonding between significantly dissimilar materials: the hard, brittle outer layer of enamel and the softer, but tougher dentine. In this study a range of experimental techniques was employed for the purpose of structure-property analysis of this naturally engineered interface. The microstructure of the DEJ was firstly investigated by Micro-Computed Tomography (Micro-CT). Two modern high-resolution X- ray synchrotron scattering analysis techniques (SAXS/WAXS) were then applied in the undisturbed state to visualize the spatial distribution of HAp crystallites across the DEJ. The insight obtained into the thermal response of DEJ is briefly discussed in the end. The systematic experimental work reported here can be used to improve the understanding of the DEJ function in terms of its complex microstructure. The knowledge of the architecture and properties of the natural DEJ will benefit the biomimetic engineering of superior dental restorations and prosthetics, and the development of novel materials to emulate the DEJ. II. STRUCTURE CHARACTERIZATION A. Micro-CT reconstruction Please check with your editor on whether to submit your The microstructure of the DEJ was firstly investigated by Micro-Computed Tomography (Micro-CT) and Environmental Scanning Electron Microscopy (ESEM) (see Fig. 1 a). The micro-CT system (SkyScan 1172 scanner, Kontich, Belgium) was used to obtain 3-D information about the tooth sample (including dentine, enamel and the DEJ). The high resolution scan was carried out at 0.6 μm resolution using 40kV voltage, 120uA current and a 0.5mm aluminium filter. The resulting 3-D slices were reconstructed with SkyScan NRECON package and were shown in Fig. 1 b. the DEJ appears to form a complex shaped interface at the micrometer scale as observed in the 3-D reconstruction and also the 2-D topography contrast image (Fig.1 c). The contrast between dentine and enamel from Fig. 1 c indicates that the interface is not sharp [2]. This visualization further approves the micro- structural feature of the DEJ that is with a series of 25–100 μm diameter scallops [3] (see Fig. 1 d). The observation from micro-CT is important in establishing Structure-Property Characterization of the Dentine-Enamel Junction (DEJ) Tan Sui, Tao Li, Michael A. Sandholzer, Eric Le Bourhis, Kaiyang Zeng, Gabriel Landini, and Alexander M. Korsunsky * F Proceedings of the World Congress on Engineering 2014 Vol II, WCE 2014, July 2 - 4, 2014, London, U.K. ISBN: 978-988-19253-5-0 ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online) WCE 2014