Purpose: To evaluate the effect of hydrothermal aging on the load to failure and number of cycles to failure of implant-supported monolithic zirconia molar crowns under cyclic loading.

Materials and methods: Twenty identical implant-supported monolithic zirconia crowns with molar morphology were produced. Half of the crowns were aged according to ISO standard 13356 to simulate 5 years in vivo. The non-aged crowns served as a control group. All crowns were subjected to cyclic loading with increasing increments of load until failure. The load to failure, the number of cycles to failure, and the failure pattern were determined for each crown.

Results: The load to failure values were 3,630 N (SD: 547.8 N) and 3,640 N (SD: 389.3 N) for the non-aged and aged crowns, respectively. The non-aged crowns failed after 33,480.1 cycles (SD: 23,138.4 cycles), and the aged crowns failed after 28,456.1 cycles (SD: 10,158.7 cycles). There was no significant difference between the two groups for the load to failure or number of cycles to failure. The predominant form of failure was catastrophic crown fracture, which was observed for all the non-aged crowns and 9 of the aged crowns.

Conclusion: Within the limitations of this study, aging of the implant-supported monolithic zirconia crowns with molar morphology did not affect the load to failure or the number of cycles to failure under cyclic loading. Since all the crowns failed at much higher loads than the expected physiologic loads, clinical application of implant-supported monolithic zirconia crowns to replace missing molars seems reasonable.