RESUMEN
Extracated human molars were used for the study, flat dentinal surfaces were prepared on the occlusal surfaces, and then 4th and 5th generation dentin bonding agents were used in dry and moist conditions to bond composite resin onto the flat dentin surfaces. Shear Bond Strength was measured using Instron Universal Testing machine. Failures were recorded as adhesive, cohesive and mixed. Bond strength was highest in moist condition, because the moist surface permits more porous collagen network and hence greater infiltration of adhesive monomers, than do surfaces that are air dried. Moreover, those dentin bonding agents whose primers are based on acetone show improved bond strength, because acetone aggressively pursues and displaces water in the substrate, resulting in the primer resin being carried into tissue channels and porosities. When the dentin is air dried, the water that is supporting the collagen network evaporates causing the collagen network to collapse network is greatly reduced, which in turn decreases the premeability of intertubular dentin to adhesive resin and as a result causes decrease in bond strength. 5th generation dentin bonding agent showed significant improvement in the moist dentin bond strength.