Mesmar S, et al. - The physicians examined the null hypothesis (H0) that material and surface treatment combinations did not affect interfacial fracture toughness (K_IC) of a self-cured adhesive resin cement [RelyX Ultimate (RXU)] to resin composite blocks (RCB) or ceramic blocks (CB), under nonaged and aged conditions. At 24 hours, interfacial K_IC of LUS-RXU and LUR-RXU was superior to EMP-RXU and EN-RXU under the conditions of this study. At 37°C, aging in water did not affect interfacial K_IC of Enamic (EN)-RXU but adversely influenced K_IC of RXU and the other interfacial K_IC.