Imaging the nanostructure of bone and dentin through small- and wide-angle X-ray scattering

X-ray scattering is a powerful nondestructive experimental method that is well suited to study biomineralized tissues such as bone. Small-angle X-ray scattering (SAXS) gives information about the size, shape, and predominant orientation of the nanometer-sized mineral particles in the bone. Wide-angle X-ray diffraction (WAXD) allows the characterization of structural parameters, describing size and orientation of the hydroxyapatite crystals. Furthermore, scanning an area with nano- or micrometer-sized X-ray beams allows one to extend this local information to map large bone or dentin sections. Therefore, this method contributes to obtaining information on several length scales simultaneously. Combining results from scanning SAXS and WAXD with those from other position-sensitive methods such as backscattered electron imaging or X-ray fluorescence spectroscopy of the same bone sections allows the exploration of complex biological processes. The method is described and illustrated by a few examples, including the mapping of a complete tooth and the effect of osteoporosis treatment on the bone mineral.