The fracture strengths of four types of all-ceramic premolar crowns (conventional Vita-Dur, In-Ceram, Dicor, and IPS-Empress) were compared after a preload cycling in aqueous atmosphere. Preload cycling significantly decreased the strength of Vita-Dur crowns. Fracture strength of Vita-Dur crowns was improved when they were luted with either polyalkenoate or adhesive resin cement. The average (standard deviation) of load to fracture of ceramic crowns luted using zinc phosphate cement and after applied preload cycling in distilled water were: Vita Dur, 770 (237) N; Vita In-Ceram, 1060 (341) N; Dicor, 840 (226) N; and IPS-Empress: 891 (185) N. The In-Ceram crowns fractured in two modes: complete fractures at 1276 (207) N; and fractures with the core remaining intact at 808 (292) N.