The theme of this program is to use structural information of bones and teeth as a basis for better understanding of formation processes and mechanical function. Two key aspects of the lamellar structure of bone will be addressed: the orientation of the crystal layers with a newly defined lamellar unit and the 3-dimensional structure of the lamellar boundary. Transmission electron microscopy (TEM), including 3-dimensional tomography, will be used for this purpose. The long term objective of developing a high resolution (+/- 50 Angstroms) cryoimmunochemical mapping technique using TEM for locating the non-collagenous proteins in bone will be pursued with the target of first mapping the distribution of bone sialoprotein. Ongoing crystal growth in bone adversely affects its fracture properties. The structural basis for this phenomenon is not well understood. With the recent advent of widespread use of the bisphosphonate, alendronate, for osteoporosis treatment, this aspect of bone structure-function relations has immediate health implications. This problem will be addressed by studying the micromechanical elastic and fracture properties of circumferential lamellar bone mineralized to different degrees in relation to its structure. Teeth are composed of a stiff outer layer (enamel) and a relatively stiff inner layer of crown dentin with its prominent peritubular dentin component. The hypothesis to be explored is that between these two layers is a softer """"""""cushion"""""""" that absorbs much of the applied stress on the tooth during normal use. Detailed maps of microhardness, as well as local strain values using Moire fringes, will be produced and then related back to tooth structure.
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