The bond strength of light-curing composite resin to finally polymerized and aged glass fiber-reinforced composite substrate

OBJECTIVE: This study examines the shear bond strength of visible light-curing composite resin (VCR) to aged glass fiber-reinforced composite (FRC) substrate with multi-phase polymer matrix. METHODS: Linear polymethyl methacrylate and dimethacrylate monomer preimpregnated unidirectional glass fiber reinforcement was used as an adhesion substrate for low-viscosity diacrylate veneering composite resin and restorative composite resin. A total of 60 test specimens were divided into three groups according to the brand and the use of an intermediate monomer resin (IMR). The used IMRs were either BisGMA-HEMA-resin, BisGMA-TEGDMA resin or the controls were left without the IMR treatment. Dry- and water-stored FRC-substrates were used for adhering the VCR with or without the IMR. The shear bond strength of the VCR to the substrate was measured for dry and thermocycled specimens and the results were analyzed with multi-variate ANOVA. RESULTS: The highest mean shear bond strength (23.9 +/- 4.8 MPa) was achieved with FRC/BisGMA-HEMA/VCR combination when the FRC substrate was water stored and the test specimen was thermocycled. FRC/BisGMA-TEGDMA/VCR combination resulted in 15.7 +/- 6.0 MPa with the water-stored FRC substrate and after thermocycling of the test specimens. The lowest shear bond strength (1.0 +/- 0.5 MPa) was obtained with FRC/VCR combination with water-stored substrate and after thermocycling of the test specimens. Significant differences were found between the mean values of three groups according to the use of IMR (p<0.001). The storage conditions of the FRC substrate were related to brand of the IMR or the composite (p<0.001). High mean values of the shear bond strength after thermocycling fatigue were related to the type of IMR (p<0.001). SIGNIFICANCE: The results suggest that the IMRs used in this study greatly influence the mean shear bond strength values when the test specimens are thermocycled.