PERMEABILITY CHARACTERISTICS OF DENTIN

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DESCRIPTION (Adapted from the investigator's Abstract): Dentin bonding generally involves the use of acid conditioners to remove the smear layer and demineralize the dentin surface to expose the underlying collagen fibers of the intertubular dentin matrix. This demineralized matrix has such a low modulus of elasticity that it can collapse if allowed to air-dry, a common clinical procedure. As it collapses, the spaces between the collagen fibers are thought to become progressively smaller and presumably less permeable, yet it is through these channels that resins must diffuse during resin bonding. If the modulus of elasticity of the demineralized matrix can be increased above a critical value, the network may not collapse when air dried, thereby remaining permeable to resin monomers. A variety of procedures will be evaluated for the ability to stiffen demineralized dentin matrix. Thus far, no one has developed quantitative methods to measure the permeation of resin into demineralized dentin. The permeability of demineralized dentin to resins in wet versus dry matrices will be measured. Dry collapsed fiber networks are thought to be less permeable to resin monomers than wet, expanded networks. The proposed studies will test that hypothesis. The effects of different acid conditioners on the permeability, tensile properties, dimensions and solubility of collagen will be tested on both demineralized dentin and tendon as examples of insoluble collagen matrices. Several different salt additives to the acidic conditioners will be evaluated to see which ones best protect collagen from denaturation. Little is known about the stability of demineralized dentin matrix over time in water. The long-term stability of demineralized dentin matrix, with or without resin infiltration, in aqueous and nonaqueous solutions, will evaluate concerns about possible hydrolytic degradation of the matrix and loss of tensile properties over time. These macroscopic results will be re-examined at the microscopic level using both SEM and an atomic force microscope modified to measure modulus of elasticity. The results of these studies will provide new information on improved formulations of acidic conditioners, how demineralized dentin should be treated with primers, how well primer resins penetrate collapsed or expanded demineralized dentin, and how well they seal and protect the collagen fibers. The results will also provide data for modeling the permeability characteristics of intertubular as well as tubular dentin.