“…The HAp crystal has an anisotropic elastic modulus, as determined by a technique based on elastic wave propagation (Gardner et al, 1992) and by nano-indentation measurements (Zamiri and De, 2011). The mechanical properties of macroscopic enamel tissue are strongly dependent on the alignment and orientation of the HAp crystals, as found from elastic modulus (Habelitz et al, 2001) and fatigue toughness (Bajaj et al, 2008) measurements. The strain behavior of HAp in mineralized tissue has been extensively studied using synchrotron X-ray sources that generate high-brightness X-rays for bone tissue Stock, 2005, 2007;Gupta et al, 2006aGupta et al, , 2006b) and for tooth dentin and tooth enamel (Almer and Stock, 2010).…”