The permeability properties od dentin are central to clinical problems such as dentin sensitivity and the pulpal reactions to caries, microleakage, dental procedures and materials. Most of our previous work has been confined to studies of occlusal dentin in young, unerupted third molars. We propose to use the same methodology to study the permeability of erupted teeth as a function of age. Occlusal, buccal, proximal and root dentin permeabilities will be compared and correlated with SEM studies of these specimens. The pulpal surfaces of coronal and root dentin will receive various treatments prior to bonding to try to optimize the bond strengths of Gluma or Superbond treated surfaces. Endodontically treated teeth may be strengthened by internal dentin bonding. During these studies, we will attempt to develop simple clinically applicable methods of estimating dentin permeability in vivo using dyes and by measuring the electrical resistance of dentin. The smear layer occupies the critical interface between materials and tooth structure. We will extend our studies of the structure and function of the smear layer by characterizing the permeability, SEM appearance practice. The microleakage of class 2 restorations will be evaluated using methods already applied to Class 1 restorations as a function of finishing procedures, post-insertion time and thermal cycling. We have recently discovered that storage of bonded specimens under a simulated physiological pulpal pressure causes the bond strength to fall 50%. These studies will be extended to include various pressures, time intervals and fluid composition in vitro and well as in vivo. We will collect smear layers for SEM and particle size analysis as well as examine the longevity of in vivo smear layers. Our previous work indicates that endogenous fibrinogen can leak from irritated pulpal blood vessels into dentinal tubules thereby decreasing dentin permeability. This hypothesis will be tested by examining the distribution of radioactive fibrinogen in vitro and in vivo in dogs using light microscopic radioautography as a function of time after cavity preparation in superficial vs deep cavity preparations before and after premedicating the dogs with dexamethasone to block the inflammatory response.