The permeability properties of dentin can have a significant influence on how teeth respond to restorative procedures and to materials. As further advances in tissue engineering are made, it is likely that a number of growth factors and other therapeutic agents will be applied to intact dentin to elicit a specific pulpal response. This may be followed by creating a surface seal with adhesive resins to prevent back-diffusion of these agents and to prevent any intratubular fluid shifts that might irritate differentiating or de-differentiating cells and the pulpodentin border. The more we understand the permeability characteristics of dentin, the more we can manipulate it for therapeutic advantage.