Project I is designed to be a systematic study of changes induced in the structure and properties of dentin as a result of storage conditions after tooth extraction and from methods used to study it. Dentin is a wet, partially organic, partially inorganic composite material that undergoes changes in structure and properties during in vitro studies, which are dependent on storage time and media, and the particular analytical method used in its analysis. Many of the most powerful analytical characterization techniques require that the dentin be under a vacuum, i.e., far from its condition in vivo, making it necessary to gauge the effects of the vacuum and desiccation on dentin characterization as well as the effects of time and of storage conditions. The hypothesis to be tested in this project is that dentin structure and properties may be substantially altered by storage conditions and analytical methods used in its study and these effects must be clarified prior to understanding the fundamental variations of the anisotropic structure itself. The specific aims are: 1) to determine the effects of various stages of dryness and vacuum on chemical, mechanical and structural characteristics of dentin; and 2) measure the effects of storage media and storage time on the physical, chemical, mechanical and structural characteristics of the dentin. We have chosen a variety of microstructural techniques and properties that should be sensitive to significant changes that might occur as a result of the main variables: time between extraction and sterilization by gamma irradiation; storage time; storage solution; drying condition. As structural electron microscopy to provide a spectrum of information relating to crystal structure, chemistry and microstructure of the dentin material. The properties measured as a function of each variable include permeability, since it relates to fluid perfusion of the dentin; microhardness, since it is a simple measure of changes in mechanical properties; and bond strength of restorative resin to dentin, since it is related to the characteristics of the restored dentin-material interface that we seek to understand and improve.