The effect of low temperature aging on the mechanical property & phase stability of Y-TZP ceramics

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Kim, Hyung-Tae; Han, Jung-Suk; Yang, Jae-Ho; Lee, Jai-Bong; Kim, Sung-Hun

Issue Date
The Korean Academy of Prosthodonitics
J Adv Prosthodont 2009;1:113-7
Low temperature agingY-TZP ceramicPhase transformationMechanical property
STATEMENT OF PROBLEM. Recently Yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) has been introduced due to superior flexural
strength and fracture toughness compared to other dental ceramic systems. Although zirconia has outstanding mechanical properties, the
phenomenon of decrease in the life-time of zirconia resulted from degradation in flexural strength after low temperature aging has been reported.
PURPOSE. The objective of this study was to investigate degradation of flexural strength of Y-TZP ceramics after various low temperature
aging treatments and to evaluate the phase stability and micro-structural change after aging by using X-ray diffraction analysis and a scanning
electron microscope (SEM). MATERIAL AND METHODS. Y-TZP blocks of Vita In-Ceram YZ (Vita Zahnfabrik, Bad Sa ¨ckingen,
Germany) were prepared in 40 mm (length) x 4 mm (width) x 3 mm (height) samples. Specimens were artificially aged in distilled water by heattreatment
at a temperature of 75, 100, 125, 150, 175, 200, and 225℃ for 10 hours, in order to induce the phase transformation at the surface.
To measure the mechanical property, the specimens were subjected to a four-point bending test using a universal testing machine (Instron model
3365; Instron, Canton, Mass, USA). In addition, X-ray diffraction analysis (DMAX 2500; Rigaku, Tokyo, Japan) and SEM (Hitachi s4700; Jeol
Ltd, Tokyo, Japan) were performed to estimate the phase transformation. The statistical analysis was done using SAS 9.1.3 (SAS institute,
USA). The flexural strength data of the experimental groups were analyzed by one-way analysis of variance and to detect statistically significant
differences (α= .05). RESULTS. The mean flexural strength of sintered Vita In-Ceram YZ without autoclaving was 798 MPa. When applied
aging temperature at below 125℃ for 10 hours, the flexural strength of Vita In-Ceram YZ increased up to 1,161 MPa. However, at above 150℃,
the flexural strength started to decrease. Although low temperature aging caused the tetragonal-to-monoclinic phase transformation related
to temperature, the minimum flexural strength was above 700 MPa. CONCLUSION. The monoclinic phase started to appear after aging treatment
above 100℃. With the higher aging temperature, the fraction of monoclinic phase increased. The ratio of monoclinic/tetragonal + monoclinic
phase reached a plateau value, circa 75% above 175℃. The point of monoclinic concentration at which the flexural strength begins to
decrease was between 12% and 54%.
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College of Dentistry/School of Dentistry (치과대학/치의학대학원)Dept. of Dentistry (치의학과)Journal Papers (저널논문_치의학과)
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