ABSTRACT
The stresses at the tooth/resin interface induced by polymerization shrinkage can weaken the bond strength and can cause gaps at the tooth/restoration interface, which will lead to microleakage around the restoration. The purpose of this study was to evaluate the bond strength of hybrid and microfilled resin composites polymerized by the 2-step technique, and to compare the results with those of the same material polymerized with the standard method of visible light polymerization A total of 60 extracted teeth were used in this study, and divided to 4 groups of 15, one control group and one test group for each resin. In the control groups, the resin samples were polymerized for 60 seconds using the standard technique at light intensity of 700 mW/cm[2]. In the experimental groups, the resin samples were polymerized using the 2-step technique at light intensity of 150 mW/cm2 for the first 10 seconds and 700 mW/cm[2] for the remaining 50 seconds. After thermo-cycling, an Instron testing machine was used for the shear bond test. To conclude based on the findings of this study, the 2-step technique helps in reducing the polymerization shrinkage stresses. But other factors that affect the flow of the material should be considered. The chance of decreasing the shrinkage stresses by the 2-step curing technique increases as the total shrinkage increases