IADR Abstract Archives
Influence of Water in Accelerated Degradation of 3Y-TZP Powder
Objectives: Tetragonal zirconia polycrystal doped with 3mol.% yttria (3Y-TZP) gradually degrades at lower temperatures to a more brittle monoclinic phase, and, thus, the longevity of 3Y-TZP restorations may be compromised. Typically, the low-temperature-degradation (LTD) of 3Y-TZP is investigated using accelerated tests in an autoclave at elevated temperatures. In this study, we examined the influence of water on LTD of 3Y-TZP powder at 134oC using synchrotron X-ray diffraction.
Methods: 3Y-TZP powder (Zpex, Tosoh) was heat treated at 1580oC for 2.5hr. Test specimens were prepared by packing powder in 1mm quartz tubing under 20 bar using compressed air. Deionized water was added to the tubing while the specimen was heated to 134oC for ~19hr to create hydrothermal conditions. To examine the influence of water, another aging test was conducted without adding water. The crystallographic structures of the zirconia powders were determined using synchrotron X-ray diffraction (51 keV) at Argonne National Laboratory. The spectra were analyzed using the Rietveld method with GSASII software.
Results: After annealing at 1580oC, the powder specimens were predominantly comprised of the tetragonal phase with no discernible monoclinic phase. The aging without added water for ~19hr resulted in ~5wt.% monoclinic phase. In contrast, the hydrothermal condition remarkably accelerated the degradation process. After ~19hr of ageing in water, a large amount of monoclinic phase was generated, as evinced by strong diffraction peaks associated with the monoclinic phase. Rietveld analysis showed that ~32wt.% tetragonal phase was transformed into the monoclinic phase while the tetragonal phase was reduced to ~68wt.%.
Conclusions: Water molecules played a critical role in the degradation of 3Y-TZP at 134oC. According to ISO 13356-2008, the monoclinic phase in dental restorations should not exceed 25%. It is not fully understood how phase transformation under hydrothermal conditions at 134oC correlates to the degradation process that occurs in a patients’ mouth.
Methods: 3Y-TZP powder (Zpex, Tosoh) was heat treated at 1580oC for 2.5hr. Test specimens were prepared by packing powder in 1mm quartz tubing under 20 bar using compressed air. Deionized water was added to the tubing while the specimen was heated to 134oC for ~19hr to create hydrothermal conditions. To examine the influence of water, another aging test was conducted without adding water. The crystallographic structures of the zirconia powders were determined using synchrotron X-ray diffraction (51 keV) at Argonne National Laboratory. The spectra were analyzed using the Rietveld method with GSASII software.
Results: After annealing at 1580oC, the powder specimens were predominantly comprised of the tetragonal phase with no discernible monoclinic phase. The aging without added water for ~19hr resulted in ~5wt.% monoclinic phase. In contrast, the hydrothermal condition remarkably accelerated the degradation process. After ~19hr of ageing in water, a large amount of monoclinic phase was generated, as evinced by strong diffraction peaks associated with the monoclinic phase. Rietveld analysis showed that ~32wt.% tetragonal phase was transformed into the monoclinic phase while the tetragonal phase was reduced to ~68wt.%.
Conclusions: Water molecules played a critical role in the degradation of 3Y-TZP at 134oC. According to ISO 13356-2008, the monoclinic phase in dental restorations should not exceed 25%. It is not fully understood how phase transformation under hydrothermal conditions at 134oC correlates to the degradation process that occurs in a patients’ mouth.