Marginal adaptation and microtensile bond strength of composite indirect restorations bonded to dentin treated with adhesive and low-viscosity composite

Abstract Objectives This study evaluated the marginal adaptation of composite indirect restorations bonded with dual curing resin cement after different strategies to seal dentin. Different bonding techniques associated or not with a low-viscosity composite resin (LVCR) were utilized. In addition, the bond strength between composite resin and pre-sealed dentin was evaluated in the buccal and pulpal walls of class I cavities, prepared for indirect restorations. Methods Thirty-three freshly extracted human molars were used for this study, divided into three groups ( n = 11) representing different techniques to seal dentin—(Group 1) Conventional technique: the adhesive system was applied and polymerized just before the cementation of the indirect restoration; (Group 2) Dual bonding technique: a first layer of the adhesive system was applied and polymerized just after preparation, and a second layer just before the final cementation; (Group 3) Resin coating technique: a LVCR was applied and polymerized after the first layer of the adhesive system, and before the impression. A further application of the adhesive system was performed before the placement of the restoration. The restorations were polished and a solution of acid red propylene–glycol was dropped on each specimen's occlusal surface for 10 s. The dye penetrations were captured under stereoscopic lens and the images were transferred to a computer with a measurement program, in order to determine the extension of the dye penetration. The microtensile bond strength test (μTBS) was applied on pulpal (P) and buccal (B) walls of the restorations for Groups 1–3. The subgroups for μTBS were: Group 1P ( n = 13); Group 1B ( n = 7); Group 2P ( n = 6); Group 2B ( n = 14); Group 3P ( n = 14); Group 3B ( n = 15). All specimens were sectioned to obtain an area of 0.8 mm2 . The specimens were mounted on a microtensile device and fractured using a universal testing machine at a cross-head speed of 1 mm/min. Failure modes were analyzed by SEM. One-way ANOVA and multiple-comparison Tukey's test were used for statistical analysis of the marginal adaptation scores and μTBS test. Non-parametrical Kruskal–Wallis test was used for failure mode analysis. Results Group 3 showed a significantly higher mean value of marginal dye penetration (45.59) when compared to Groups 1 (8.44) and 2 (18.92). For pulpal walls, Group 1P showed significantly higher mean μTBS (25.93 ± 2.27) when compared to Groups 2P (14.71 ± 1.78) and 3P (16.0