OBJECTIVES: Objectives of this study were to evaluate and compare the failure load and mode of failure of aged (4 years) monolithic and veneered Y-TZP and glass ceramic subjected to static loading, cyclic loading, and thermo-cycling. MATERIALS AND METHODS: 2 ceramic materials were used: Vita In-Ceram YZ and IPS e. max CAD. Each material was designed into 60 veneered copings and 30 monolithic crowns (180 specimens). 10 specimens per group were loaded under compression using an Instron universal testing machine at a rate of 0.5 mm/minute until fracture. Another 10 specimens were subjected to cyclic loading (chewing simulation) in a water bath for 50,000 cycles at a frequency of 1 Hz at 30% of the mean failure load, and then were loaded under compression to fracture. Another 10 specimens were subjected to a thermo-cycling test, then loaded under compression to fracture. Data were analyzed using the ANOVA test at α=0.05. RESULTS: The mean failure load (standard deviation) values for veneered zirconia and e.max CAD copings and monolithic zirconia and e.max CAD crowns under static loading were: In-Ceram YZ 14830 N (2494), VM9 2491 N (1047), PM9 3909 N (783), IPS e.max CAD 4197 N (1011), IPS e. max Ceram 1206 N (296), IPS e.max press 2949 N (710). The values for veneered standard zirconia and e.max CAD copings and monolithic zirconia and e.max CAD crowns after cyclic fatigue were: In-Ceram YZ 11039 N (2720), VM9 2849 N (840), PM9 3170 N (1156), IPS e.max CAD 3539 N (526), IPS e. max Ceram 1291 N (1051), IPS e.max press 3093 N (742). For veneered standard zirconia and e.max CAD copings and monolithic zirconia and e.max CAD crowns after thermo- cycling: In-Ceram YZ 15695 N (1517), VM9 3177 N (816), PM9 2860 N (783), IPS e.max CAD 4265 N (681), IPS e. max Ceram 1149 N (375), IPS e.max press 2832 N (717). There was a significant difference in failure load between veneered and monolithic ceramic crowns subjected to static loading, cyclic loading, and thermo-cycling, and a significant difference in the mode of failure between veneered or monolithic crowns. CONCLUSIONS: 1. There was a significant difference in the static failure load of different veneered (Hand layered and pressed-on) YTZP zirconia and e.max CAD copings, monolithic YTZP zirconia, and e.max CAD Crowns, (p < 0.05). 2. The highest static failure loads were shown by high strength monolithic (In-Ceram YZ) material, which were more resistant to cyclic loading compared to other veneered and monolithic systems. 3. The failure load of IPS e.max ceram group was significantly the lowest compared to all other groups. 4. The failure load data for IPS e.max CAD and Vita In-Ceram YZ structures revealed a significant difference in the effect of these structures on the failure loads (p < 0.05). Comparing structures, monolithic Vita In-Ceram YZ crowns showed the highest failure load. 5. There was a significant difference in failure mode among various veneered and monolithic systems (p < 0.05). Only the variable treatment had no impact on the mode of failure of various veneered and monolithic systems (p > 0.05). / 2020-10-24T00:00:00Z