© 2015 American Dental Association. Background The purpose of this study was to determine the presence of a correlation between flexural strength and simulated crown strength; a correlation between crown strength and mode of fracture; an effect of aging on the flexural strength; and an effect of aging on the crown strength. Methods Two hundred forty zirconia specimens were fabricated with 2 different designs, fully contoured crown shape specimens (n = 120) and rectangular coupons (n = 120), to provide 10 specimens each of 6 brands of zirconia (Lava Plus High Translucency [3M ESPE], Argen HT [Argen Corp], Zirlux [Ardent], BruxZir [Glidewell Laboratories], ZenoStar [Wieland Dental], and DDBioZX2 [Dental Direkt]). One-half of each sample type was given a severe, simulated low-temperature aging treatment. The coupons were tested by 3-point flexural strength, and crowns were tested after luting to metallic abutments using resin cement. Statistical significance was evaluated by 2-factor analysis of variance (P =.05). Results Aging increased the mean (standard deviation [SD]) flexural strength for the following groups: Argen HT (995  megapascals versus 677  MPa before aging), Zirlux (939  MPa versus 826  MPa before aging), and ZenoStar (954  MPa versus 764  MPa before aging). There were statistical differences for the mean (SD) crown strengths for the following aged crowns: DDBioZX2 had higher magnitudes (9,755 [1,095] MPa) than ZenoStar (8,864  MPa), whereas Lava Plus High Translucency crowns had higher magnitudes (9,871  MPa) than ZenoStar (8,864  MPa). There was no effect of aging on the crown strength. There were statistical differences in the mode of fracture for the zirconia crowns between the following groups: nonaged and aged BruxZir (P =.014), nonaged and aged ZenoStar (P =.0226), and nonaged and aged Lava Plus High Translucency (P <.0001). There was no correlation between flexural strength and crown strength. Conclusions There was no direct correlation between ranking of flexural strength and crown strength in the range of properties exhibited by these dental zirconias. Practical Implications Flexural strength does not predict simulated clinical strengths for crowns.