Advancements in the development of aesthetic porcelains have lead to their use in applications that may be contra-indicated by the manufacturer. Objective: The objective of this study was to analyze the fracture resistance of two veneering ceramics bonded to substrates with different elastic moduli. Methods: Porcelain discs (16.9mmx1.5mm,n=40) were made from ^IPSd.sign (D) ceramic (Ivoclar North America, Inc., Amherst, NY) and Ceramco II (C) ceramic (Ceramco, Burlington, NJ) according to the manufacturers instructions. Specimens were polished through 1µm Al₂O₃. Two epoxy resins with different elastic moduli, Epoxofix Resin (ER) (Struers, A/S Denmark) (n=20) and blue Die Epoxy (EB) (American Dental Supply, Easton,PA) (n=20) were selected as substrate resins. Each disc was bonded using Variolink cement (Vivadent, Schaan, Liechtenstein) to substrates of similar dimensions under a static load of 22.5N. Each of 10 specimens in one of four groups, D/ER, D/EB, C/ER, C/EB, was loaded to failure at a crosshead speed of 0.5mm/min. A dynamic modulus testing unit (Ultran Labs/Nuson Inc., Boalsburg, PA) was used to measure the elastic moduli (E). Results: ANOVA revealed a significant difference among mean failure loads for the two ceramic groups F(3,36)=209.5, p=0.00. The mean failure loads (and standard deviation values) of the groups were; D/EB=38.1 N (6.9); D/ER=68.6 N (15.3); C/EB=197.2 N (37.6); C/ER=534.4 N (90.4). E for each material was D=66.5 GPa; C=67.1 GPa; EB=11.8 GPa; ER=5.2 GPa. Tukey's HSD indicates there was no significant difference in the mean failure load for ceramic D on either substrate (p=0.524), however there was a significant difference for group C ceramic specimens (p=0.05). Conclusion: The results of this study indicate that the mean fracture resistance of ceramic D was significantly lower than that of ceramic C, although the mean failure load of ceramic C was affected by the elastic modulus of the substrate. Supported by NIH/NIDCR DE06672.

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