Correlation of flexural strength of coupons versus strength of crowns fabricated with different zirconia materials with and without aging

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 DDBioZX(2) [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 [140] megapascals versus 677 [121] MPa before aging), Zirlux (939 [101] MPa versus 826 [169] MPa before aging), and ZenoStar (954 [81] MPa versus 764 [77] 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 [976] MPa), whereas Lava Plus High Translucency crowns had higher magnitudes (9,871 [942] MPa) than ZenoStar (8,864 [976] 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.