The Effect of the Shade of Indirect Restorations on the Microtensile Bond Strength of Dual-curing Resin Cements Using a Touch-cure System to Dentin

<p> Purpose: Recently, dual-curing resin cements and self-etch adhesives have been increasingly used for indirect esthetic restorations to ensure optimal polymerization of resin cements and adhesives. However, attenuated light irradiation intensity may lead to severe clinical problems, because the polymerization of dual-curing resin cements and self-etch adhesives is greatly affected by the light-curing method. Some resin cement systems include catalysts both in resin cements and adhesives and the chemical copolymerization is facilitated when the adhesive comes in contact with the corresponding resin cement (touch-curing system), in order to improve the copolymerization of resin cements and adhesives. The purpose of this study was to evaluate the effects of the shade of indirect restorations on microtensile bond strengths (μTBSs) of resin cements using a touch-curing system to dentin.</p><p> Methods: Twenty-four extracted human molars were randomly assigned to four experimental groups according to the four resin cements used in this study, which were PANAVIA V5 (PV) and Rely X Ultimate Adhesive Resin Cement (RU) as dual-curing resin cements using a touch-curing system, ESTECEM (EC) as a self-curing resin cement, and Rely X Veneer Cement (RV) as a light-curing resin cement. Indirect restorations were fabricated from resin composites (Pearl Este, shade DA2 and ODA2). After applying the corresponding adhesive of each resin cement to flat dentin surfaces and corresponding primer to resin discs, the resin discs were bonded to the dentin using each resin cement, and cured using a halogen light-curing unit. After storage in distilled deionized water at 37°C for 24 h, the specimens were sectioned into approximately 0.7×0.7 mm² pieces. Following that, each specimen was subjected to the μTBS test and the results were statistically analyzed using a t-test with Bonferroni correction (α=0.05). After testing, the fracture modes were determined and statistically analyzed using the Chi-square test (α=0.05).</p><p> Results: In only the RV, which is a light-curing resin cement, there was a significant difference between the μTBSs of the DA2 and ODA2 groups. In both shade groups, the μTBS of PV, which uses a touch-curing system, was significantly higher than that of the other resin cements, and the μTBS of RV was significantly lower than that of EC and RU. The Chi-square test revealed no significant differences between the fracture modes of the DA2 and ODA2 groups in all resin cements.</p><p> Conclusion: Within the limitations of this study, the shade of indirect restorations does not affect the dentin bond strength of dual-curing resin cements using the touch-curing system. This suggests that the touch-curing system may achieve adequate polymerization of dual-curing resin cements by attenuated light irradiation.</p>