Do different time intervals in placement of restorative materials over calcium silicate cements, affect interface microhardness of different restorative materials?

Objectives: The type of materials and application time of final restorations on calcium silicate cements (CSCs) are important factors which influence the interfacial properties. The aim of this study was to investigate the effect of different placement time of RMGI (Resin Modified Glass Ionomer), composite resin and amalgam over different CSCs on the surface microhardness of these restorative materials.Methods: Each CSCs material (Biodentine, MTA, CEM cement) was mixed and carried into a hole (6mm diameter ×4 mm thickness) in the center of 270 molds (n=90 /each CSC). Then these molds were randomly divided into three main experimental groups (n=30) in regard of restorative materials (Amalgam, RMGI, Composite) that were placed in the other molds with the same hole size to make restorative materials and CSCs in contact together. Afterwards, each experimental group was divided into three subgroups according to the time interval of restoration placement that was immediately, after 24h and after 72h (n=10). Two molds were separated from each other after one week storage in incubator with 100% humidity in 37 °C, in order to evaluate the Vickers microhardness of restorative materials in CSC-restorative material interface. Statistical analysis included two-way Anova followed by Post hoc Dunnett T3 in cases with lack of homogeneity and Tukey HSD in cases with homogeneity.(p=0.05)Results: The microhardness of all restorative materials was neither significantly influenced by the CSCs materials (p>0.05) nor by the timing of final restoration (p>0.05) except in RMGI in immediate contact with CEM cement. (p<0.001)Conclusion: Restorative materials hardness in interface with studied CSCs may not affect. This in vitro study found no evidence against immediate definitive restoration over CSCs.