Low temperature degradation of yttria stabilized tetragonal zirconia polycrystalline ceramics (Y-TZP)
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Objectives To evaluate effect of water and surface treatments on strength and microstructure of Tosoh Y-TZPs Materials and methods Three types of Tosoh Y-TZP powders (Tosoh Corporation, Japan) were used: TZ-3YSB-E(Standard), TZ-PX242A(Zpex) and TZ-PX418(Zpex smile). All powders were pressed uniaxially in a 19 mm diameter steel mold @ 78 MPa (11 ksi) and then isostatically pressed at 138 MPa (20 ksi). The bIocks were then sintered to approximately 50% theoretical density and sliced to produce discs. Discs were sintered at 1500[degrees]C forTZ-3YSB-E and 1450[degrees]C forTZ-PX242A and TZ-PX418 to full density following manufacturer’s firing schedules using a Vita ZYrcomatT furnace (Vita Zahnfabrik). Final dimensions of each disc were about 15 mm diameter and 1.2 mm thick. Water treatments Specimens were divided into 8 groups for each type of Y-TZP; as sintered and 7 groups were exposed to water vapor for various times. The specimens were separated from water by steel wool then kept at 134[degrees]C and 2 atm for 15 minutes 1, 2, 5, 10, 24 and 168 hours to simulate steam aging process. (N=10/group) Surface treatments 5 groups were as sintered, treated by 50 micron sandblasting, grinding with 35, 125 and 240 [mu]m diamond wheels. (N=10/group) Monoclinic content analysis was done using D8 Bruker diffractometer. BiaxiaI flexural strength was determined using a ball on three ball apparatus at a cross head speed of 1 mm/min. Statistical analysis was performed using ANOVA and Tukey posthoc test for multiple comparison. Results Mean biaxial flexural strengths of were TZ-3YSB-E 1161.7 [plus or minus] 87.10,TZ-PX242A 1067.1 [plus or minus] 100.42 and TZ-PX418 817.5 [plus or minus] 73.67 MPa. After steam exposure, there was no significant change in mean biaxial flexural strength. Sandblasting increased biaxial flexural strength of TZ-3YSB-E 27% and TZ-PX242A 37% and decreased biaxial flexural strength of TZ-PX418 by 57%. Grinding with 35, 125 and 240 [mu]m diamond had no significant effect on biaxial flexural strength of TZ-3YSB-E but did increase biaxial flexural strength of TZ-PX242A by 18.55-22.21%. Grinding with 35 [mu]m diamond had no significant effect on biaxial flexural strength of TZ-PX418, but grinding with 125 and 240 [mu]m diamond decreased biaxial flexural strength 43.70% and 62.42% respectively. Artificial steam aging had a significant role in increasing monoclinic phase of Tosoh 3Y-TZP (TZ-3YSB-E and TZ-PX242A) over time, but not 5Y-TZP (TZ-PX418). All surface treatments had a significant role in increasing a small amount of monoclinic phase of Tosoh 3Y-TZP (TZ-3YSB-E and TZ-PX242A) but not 5Y-TZP (TZ-PX418). Conclusions There were some significant differences in biaxial flexural strength values between different Tosoh Y-TZP ceramics. Artificial steam aging had no significant effects on biaxial flexural strength of all Tosoh Y-TZP, whereas, surface treatment had a significant effect on biaxial flexural strength of Tosoh Y-TZP. AII steam and surface treatments had a role in increasing monoclinic phase of Tosoh 3Y-TZP (TZ-3YSB-E and TZ-PX242A) but not 5Y-TZP (TZ-PX418).
PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact email@example.com.Thesis (DScD) --Boston University, Henry M. Goldman School of Dental Medicine, 2015 (Department of Restorative Sciences and Biomaterials).Includes bibliography: leaves 126-131.
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