Influence of primers on the properties of the adhesive interface between resin composite luting cement and fiber-reinforced composite

Objectives: The purpose of this study was to characterize the adhesive interface formed due to the dissolving capability of 4 primer systems into pre-polymerized semi-interpenetrating polymer network (semi-IPN)-based fiber-reinforced composite (FRC) and luting cement. Materials and methods: Semi-IPN FRC (everStick C&B, StickTech) prepregs stored for various durations (at 4 degrees C; 1, 1.5, and 3 years) were used to fabricate the specimens. FRC specimens (n = 10) were light-cured and treated with primers before adhering a luting cement onto them. Each age group was divided into four subgroups according to the primer used: no priming, a dimethacrylate adhesive primer, universal primer, and primer intended for composite surfaces. The degree of monomer conversion (DC%) of the luting cement; nanohardness, elastic modulus and structural information of the luting cement FRC adhesive interface were measured. Results: According to analysis of variance (P <= 0.05), no statistical difference was observed in the DC% among the tested groups. However, both universal and composite primers showed increased nanohardness in 1- and 1.5-year-aged groups. The highest nanohardness (0.55 +/- 0.21 GPa) and elastic modulus (14.27 +/- 5.19 GPa) were observed in specimens of 1-year-aged FRC primed with the application of universal primer. Raman spectroscopy and scanning electron microscopy examination confirmed the presence of poly(methyl methacrylate) at the interface when the FRC prepregs were aged for 3 years before use. Conclusion: Both primers improved diffusion of monomers of composite luting cement into the polymerized semi-IPN polymer structure and possible covalent binding with pendant methacrylate groups in the polymer matrix of FRC. The diffusing capability of universal and composite primers might increase the opportunity to form solid adhesive interface bonding between the FRC and composite luting cement.