Objectives This study evaluated the effects of light exposure through simulated indirect ceramic restorations (SICR) on hardness (KHN) of dual-cured resin cements (RCs), immediately after light-activation and 24 h later. KHN analysis immediately and 24 h after light-activation. The data obtained at the 2 2 evaluation intervals were submitted to 2-way ANOVA repeated measures and Tukeys test (pre-set alpha of 5%). Results Lower KHN was observed when light-activation was performed through SICRs for eco-Link at all evaluation intervals and for Rely X ARC 24 h later. For Panavia F, no significant difference in KHN was observed between control and experimental groups, regardless of evaluation interval. Most groups exhibited higher KHN after 24 h than immediately after light-activation, with the exception Jatrorrhizine Hydrochloride of Rely X ARC light-activated through SICR, as no significant difference in KHN was found between evaluation intervals. Conclusion Light overexposure did not compensate for light intensity attenuation due to the presence of SICR when Rely X Jatrorrhizine Hydrochloride and eco-Link were used. Although hardness of such RCs increased over a 24-h interval, the RCs subjected to light overexposure did not reach the hardness values exhibited after direct light exposure. Keywords: Dual-curing of resin cements, Hardness, Ceramics INTRODUCTION Indirect ceramic restorations have been chosen as better options than direct resin composite restorations to restore wide dental cavities, such as large inlay and onlay restorations24,30. The main advantages of indirect ceramic over direct resin composite restorations are the better wear resistance, lower stain susceptibility and the ability to simulate enamel aesthetical Mouse monoclonal to BNP features13. For this reason, indirect ceramic restorations became one of the most important and popular clinical procedures in the last few years24. Adhesion of most types of glass ceramic restorations to tooth structure can be obtained by the use of resin cements (RCs)16, as they show a reliable bonding to the tooth substrates, low solubility, and optimal aesthetics13,18,22,23. Furthermore, when compared to glass ionomer and zinc phosphate cements, resinous materials provide higher fracture strength values to fatigue when used to bond metalfree ceramic crowns, ceramic inlays and onlays to the Jatrorrhizine Hydrochloride prepared tooth14. Dual-cured RCs were developed in an attempt to combine the desirable physical properties obtained from chemical and light polymerization6, and to allow proper monomer conversion at deep areas where the activation light is usually attenuated or totally absent20. Ceballos, et al.6 (2007) demonstrated that dualcured RCs present better mechanical properties than self- and light-cured RCs. However, some authors have reported that dual-cured RCs cannot achieve proper polymerization and acceptable mechanical properties when they rely solely around the self-curing mode15,28. An optimal monomer conversion of RCs is crucial to assure the ideal physical properties and durable clinical performance of the indirect ceramic restoration on the tooth19. Conversely, poor polymerization impairs the cement physical properties, Jatrorrhizine Hydrochloride so low bond strength, high water absorption and compromised shade stability are expected as a consequence19. In addition, low monomer conversion allows the release of toxic substances from the polymer to the pulp due to the poor polymeric chain formation8,10,20. Low monomer conversion of dual-cured RCs has also been observed when activation light is usually attenuated by the presence of indirect ceramic restorations as the self-curing components are not able to compensate for the low light intensity that reaches the resinous material4,15. For this reason, light-activation of dual-cured RCs through ceramic discs with thickness ranging from 1 to 5 mm results in lower cement hardness, which has been considered an indirect assessment of monomer conversion5,8,10. The authors also observed that this decrease in hardness was more evident when the ceramic restorations were thicker than 4 mm. Therefore, the authors concluded that the thickness of the indirect ceramic restoration is related to the decrease in cement hardness. Polymerization in deep cavities located Jatrorrhizine Hydrochloride on mesial and distal areas, where indirect ceramic restorations are thicker, deserves more concern as the activation light is usually transmitted through at least 4 mm of indirect restoration to reach the RC layer, so the RC relies mostly upon the self-curing mode9. Based on such issue, manufacturers recommend to lightactivate the RC not only from the occlusal surface, but also from buccal and lingual surfaces. However, most studies.