Effect of Intermediate Adhesive Resin and Flowable Resin Application on the Interfacial Adhesion of Resin Composite to Pre-impregnated Unidirectional S2-Glass Fiber Bundles

Purpose: This study evaluated the effect of either an intermediate application of adhesive resin or flowable resin application on the adhesion of particulate filler composite (PFC) to glass fiber-reinforced composite (FRC). Materials and Methods: Unidirectional, pre-impregnated S2-glass fiber bundles (Dentapreg) (length: 40 mm; thickness: 0.5 mm) were obtained (N = 30, n = 10 per group) and secured in translucent silicone material with the adhesion surface exposed and photopolymerized. They were randomly divided into 3 groups for the following adhesion sequence: A) FRC+PFC, B) FRC+intermediate adhesive resin+PFC, C) FRC+flowable resin+PFC. The PFC was applied in a polyethylene mold onto the FRC and photopolymerized. PFCs were debonded from the FRC surface using shear bond test in a universal testing machine (1 mm/min). After debonding, all specimens were analyzed using scanning electron microscopy to categorize the failure modes. The data were statistically analyzed using one-way ANOVA and Tukey's tests (α = 0.05). Results: A significant difference was observed between the groups (p 0.05). The highest mean bond strength value was obtained with the application of an intermediate layer of adhesive resin (group B: 19.4 ± 1.1 MPa) (p 0.05) followed by group A (14.1 ± 0.6 MPa) and group C (10.4 ± 0.8 MPa), which were also significantly different from one another (p 0.05). Group A exclusively presented a combination of partial cohesive failure in the PFC and adhesive failure between the FRC and PFC. While group B showed large cohesive defects in the FRC, in group C, only small cohesive failures were observed in the FRC. Conclusion: Based on the highest mean bond strength and the large cohesive failures within the FRC, application of an intermediate layer of adhesive resin on the S2-glass FRC surface prior to incremental build up of the PFC seems to be compulsory. Keywords: adhesion, bonding agent, bond strength, dental materials, intermediate adhesive resin, fiber-reinforced composites, flowable resin