Hindawi Publishing Corporation ISRN Biomaterials Volume 2013, Article ID 253761, 15 pages http://dx.doi.org/10.5402/2013/253761 Research Article Mechanical Properties of Enamel Nanocomposite Nilormi Biswas, 1 Arjun Dey, 2 Saugata Kundu, 3 Himel Chakraborty, 4 and Anoop K. Mukhopadhyay 1 1 CSIR-Central Glass and Ceramic Research Institute, Kolkata 700032, India 2 Termal Systems Group, ISRO Satellite Centre, Vimanapura, Bangalore 560 017, India 3 IBM India Pvt. Ltd., Rajarhat, Kolkata 700156, India 4 School of Materials Science and Engineering, Bengal Engineering and Science University, Shibpur, Howrah 711103, India Correspondence should be addressed to Anoop K. Mukhopadhyay; anoopmukherjee@cgcri.res.in Received 10 December 2012; Accepted 9 January 2013 Academic Editors: S. M. Cer´ e, J. Toppari, and X. Wang Copyright © 2013 Nilormi Biswas et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. For adult Indian premolar teeth, we report for the frst time ever the simultaneous evaluations of nanohardness, Young’s modulus, and fracture toughness of the enamel nanocomposite. Te nanohardness and Young’s moduli were evaluated from near the beginning of the middle enamel region to within ∼10 m of the dentino-enamel junction (DEJ) and in the dentin region using the nanoindentation technique. Te fracture toughness from near the middle of the enamel region to near the DEJ zone was measured using the microindentation technique. Te deformation was studied using scanning electron microscopy (SEM) and feld emission scanning electron microscopy (FESEM). Te relative diferences in the extents of biomineralization in the enamel and dentin regions were studied by the energy dispersive X-ray (EDS) technique. Te variations of the toughness of the enamel as a function of the toughness of the protein matrix phase have been analyzed which showed that the predicted value of the toughness of the protein present in the nanocomposite was comparable to that of other bioproteins reported in the literature. Further, the work of fracture estimated from the measured value of toughness of the enamel nanocomposite agreed well with the experimental data reported in the literature. 1. Introduction Tooth is a microscopically functionally graded calcium phos- phate based natural biocomposite material (Figure 1). Fur- thermore, tooth has also a hierarchical architecture, for exam- ple, from macrostructure to microstructure to nanostructure (Figure 1). Te tooth is composed of mainly the hard enamel, the more ductile dentin, and a sof connective tissue, the den- tal pulp. Enamel is the hardest structure in the human body with approximately 95 wt% hydroxyapatite (HAP). On the other hand, dentine possesses a porous structure and is made up of ∼70% inorganic material (i.e., HAP), ∼20% organic materials (i.e., collagen fber), and ∼10% water by weight. Te enamel microstructure shows diferent orientations of closely packed enamel prisms or rods. Tese rods are encapsulated by an organic protein called enamel sheath. Further, the prisms or rods consist of nanosize inorganic HAP crystals with diferent orientations inside. On the other hand, the dentine has a collagen matrix reinforced with HAP nanocrystal retained as layer by layer. Te composite bed of dentine also has dentine tubules and channel-like microstructures which supply the nutrition from the pulp region to the crown part of the teeth. In contrast, the interface between the enamel and dentin junction (DEJ) is arranged with dome-shaped excavations. Terefore, the irregular interface interlocks the two tissues, for example, enamel and dentine. Te denti- noenamel nanocomposite junction (DEJ) surface is highly scalloped and has pits into which the shallow depressions of the dentin ft the circular projection of the hard enamel nanocomposite, thus making the enamel nanocomposite cap hold frmly on the dentin [1]. As a result of mastication, the occlusal enamel nanocomposite region and the proximal contact points experience changing loading rates. During high occlusal loading, cracks may be generated in the enamel nanocomposite region, but they rarely propagate across the DEJ into dentin to fracture the entire tooth. Te DEJ is