In vitro evaluation of the bond strength of composite resin foundation materials to dentin

Statement of problem. Achieving adequate bonding of composite resin foundation materials to dentin can be a challenge. Bonding can be affected by the type of bonding material and method used. Purpose. The purpose of this in vitro study was to test the bond strengths of selected dual-polymerizing composite resin foundation materials to dentin using light, chemical, or dual-polymerized adhesive systems. Material and methods. Eighty freshly extracted human third molars were sectioned vertically into mesial and distal halves and embedded in acrylic resin using a copper cylinder. Specimens were divided into 16 groups. Each group received a resin foundation that was bonded to dentin according to each manufacturer's instructions. All tested foundations were dual polymerized except Tetric Ceram, which was light polymerized. BisCore, Build-it, CompCore, CoreRestore, and FluoroCore resin foundation materials were bonded to dentin with the use of the corresponding adhesives in 3 different bonding methods: adhesive was light polymerized; adhesive was chemically polymerized; and adhesive was dual polymerized. Each specimen was seated in a custom shear test device, and a load was applied with the descending rod of the jig from a mechanical testing machine with a perpendicular force to the dentin-adhesive interface. Statistical analysis was performed using 2-way ANOVA and post hoc pairwise comparison with Tukey test when statistically significant differences were found (alpha=.05). Results. Resin foundation materials bonded to dentin with light-polymerized adhesives produced significantly higher bond strengths than when bonded with chemically or dual-polymerized adhesives. No significant difference was found between the single-component and multiple-components adhesives used with Tetric Ceram and BisCore foundations (P=.083). However, BisCore used with All-Bond 2 adhesive (multiple components) produced significantly lower bond strengths than when used with One-Step (P=.024). Adhesive failure was the most common failure location. Cohesive failures occurred mostly in specimens bonded with light-polymerized adhesives. Conclusions. The light-polymerized adhesives tested produced significantly higher bond strengths when used without chemical activators. The dual-polymerized core foundations produced better bond strengths to dentin when used with light-polymerized adhesives without chemical activators. In comparing single-component with multiple-component adhesive systems with their respective core resins, no difference was found in bond strengths to dentin.