Creep mechanisms in bone and dentin via high-energy x-ray diffraction

Bone and dentin are highly complex, hierarchical composite materials with exceptional properties due to their unique composition and structure. They are essentially the same material with varied structural organization. They are three phase composites made up of a ceramic component, hydroxyapatite (HAP), a polymeric or proteinaceous component, collagen, and fluid filled porosity. A number of macroscopic studies have shown that both dentin [1-6] and bone [7-9] undergo visco-elastic, creep deformation and stress-relaxation behaviors. The problem with these bulk experiments is that they do not give information about which phase is contributing to the macroscopic creep or how. Some of these inquiries have suggested that the collagen is not responsible [9] and that creep in hard biological materials is primarily due to dislocations in the HAP mineral. On the other hand, others have said that collagen is completely responsible for the creep [8, 10]. These uncertainties make it essential to use techniques that allow for the study of the behavior of these very different components simultaneously during loading, determining their participation in creep. One such technique is synchrotron diffraction.