Effect of Thermal and Mechanical Aging on Flexural Strength of Zirkonzahn and Mamut Zirconia Ceramics

  Objective: Despite the high strength of zirconia restorations, aging in the oral environment and masticatory loading may result in transformation of tetragonal to monoclinic phase and decrease their strength. Statements in this regard are controversial. This study sought to compare the flexural strength (FS) of Zirkonzahn (ZirkonZahn, Cercon, Ceramill) and Mamut (Dubai Medical Equipment LLC, Dubai, UAE) zirconia ceramics and assess the effect of thermal and mechanical aging on their FS.   Methods: In this in vitro experimental study, 40 bar-shaped specimens measuring 20×5×2 mm were cut from Zirkonzahn and Mamut zirconia blocks and polished. Specimens in the aging groups were subjected to thermocycling (12,000 cycles, 5-55°C, dwell time of 20 seconds). Next, they were subjected to mechanical stress in a chewing simulator (40,000 cycles, 200N force). The three-point flexural strength (TPFS) was determined in megapascal (MPa) using a Universal Testing Machine at a crosshead speed of 0.5 mm/min. Data was analyzed using two-way ANOVA.   Results: The mean and standard deviation (SD) of TPFS of Zirkonzahn and Mamut specimens in the no aging group was 809.57 (205.95) and 708.53 (158.72) MPa, respectively. These values were 810.53 (158.96) and 839.06 (217.49) MPa for the Zirkonzahn and Mamut specimens subjected to aging, respectively. Type of zirconia (Zirkonzahn or Mamut) and exposure to aging process (p=0.27) had no significant effect on TPFS of specimens.   Conclusion: Within the limitations of this study, the results showed that the process of aging did not decrease the TPFS of Zirkonzahn and Mamut specimens. Thus, these ceramics may be successfully used in the clinical setting.