In vitro investigation and evaluation of dentin bonding agents.

The development of dentin bonding agents has made the adhesion between composite restorative resins and dentin possible. Laboratory studies involving microleakage and bond strength tests are carried out to predict the longevity of composite resin restorations in the clinical situation. Microleakage at the restoration/tooth interface may result in breakdown at the margins of restorations, the development of secondary caries at the restoration/tooth interface and pulp pathology. The methods to evaluate microleakage and marginal gap formation at the dentin/ restoration interface in laboratory studies are reviewed. The effects of polymerization shrinkage, differences in the coefficients of thermal expansion, and restorative techniques on these parameters are discussed. Tensile and/or shear bond strength tests are usually performed to predict the retention of composite restorations clinically. Some of these test methods routinely used in our laboratory are described. The shear bond strengths of dentin bonding agents to dentin are dependent on the test methodology. Both the laboratory microleakage and shear bond strength test vary tremendously. An appeal is made for the standardization of these test methods. Attempts should be made to establish a correlation between in vitro and in vivo evaluations.