The crystallographic influence of hydroxyapatite (HA) on dissolution was investigated by X-ray diffraction (XRD) and X-ray pole figure (XPF). All HA disks were sintered at 1200 degrees C for 2 h in air with moisture protection and were immersed in 40 ml of pH 7.4 distilled water at 37 degrees C. In addition to the surface dissolution at grain boundaries, grains themselves were degraded in a specific direction showing the aligned crystallites. XRD analysis showed that the peak intensity of (300) was maintained relatively during immersion compared with the rest of the peaks. XPF analysis revealed that the contour lines of (211) and (112) decreased after immersion, whereas the (300) contour line remained similar before and after immersion. This means that the (300) plane of HA could be relatively stable in a liquid environment. Therefore, it may be concluded that the direction of crystal alignment should be associated with the susceptibility of certain ceramic grains to dissolution.

Keywords: hydroxyapatite; crystal alignment; dissolution; X-ray pole figure