• Restorative Dentistry and Endodontics
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• v.45 no.4
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• pp.52.1-52.11
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• 2020

Objectives: Yttria-stabilized tetragonal phase zirconia has been used as a dental restorative material for over a decade. While it is still the strongest and toughest ceramic, its translucency remains as a significant drawback. To overcome this, stabilizing the translucency zirconia to a significant cubic crystalline phase by increasing the yttria content to more than 8 mol% (8YTZP). However, the biocompatibility of a high amount of yttria is still an important topic that needs to be investigated. Materials and Methods: Commercially available 8YTZP plates were used. To enhance cell adhesion, proliferation, and differentiation, the surface of the 8YTZP is sequentially polished with a SiC-coated abrasive paper and surface coating with type I collagen. Fibroblast-like cells L929 used for cell adherence and cell proliferation analysis, and mouse bone marrow-derived mesenchymal stem cells (BMSC) used for cell differentiation analysis. Results: The results revealed that all samples, regardless of the surface treatment, are hydrophilic and showed a strong affinity for water. Even the cell culture results indicate that simple surface polishing and coating can affect cellular behavior by enhancing cell adhesion and proliferation. Both L929 cells and BMSC were nicely adhered to and proliferated in all conditions. Conclusions: The results demonstrate the biocompatibility of the cubic phase zirconia with 8 mol% yttria and suggest that yttria with a higher zirconia content are not toxic to the cells, support a strong adhesion of cells on their surfaces, and promote cell proliferation and differentiation. All these confirm its potential use in tissue engineering.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.04b
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• pp.23-27
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• 1995

In sawing operation of synthetic jewelry, the performance of diamond cutter blade is very dependent on the blade variables. This investigation presents ecperimental results which show the effects of the blade variables such as types of diamond abrasives, grain size of diamond, concentration, and bond materials on the beavior of te blades. Based on the experimental results an optimum blade condition for the sawing of cubic zirconia was recommended.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.10
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• pp.3621-3625
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• 2010

Colored cubic-zirconia specimens made by skull melt process were annealed in vacuum at the temperature of $1200^{\circ}{\sim}1400^{\circ}C$ for 10~60 minutes to enhance the color. The three different colored specimens become darker and eventually are black as annealing temperature and time increase. Conventional gem stone grading method and XPS were employed to quantify the property change and to reveal the mechanism of the color change. Color was changed apparently but the hardness and apparent density did not vary with annealing. Based on XPS result, we concluded that the main cause of the color change in cubic zirconia might be the change of Y-O bonding energy state of $Y2_O_3$ phase-stabilizer by vacuum annealing.

• Journal of the Korean Ceramic Society
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• v.38 no.9
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• pp.834-838
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• 2001

Attempts were made to improve mechanical properties of zirconia-based electrolyte by preparing yttria-stabilized cubic zirconia/alumina composite. It was performed by precipitating Yag precursor in aqueous m-zirconia slurry. The powder was separated and then followed by heat treatment with expecting yttria to react with m-$ZrO_2$ to give yttria stabilized zirconia and alumina to be dispersed homogeneously. When 17.8wt% Yag(6.3mol% $Y_2O_3$) was used, fracture toughness and strength were substantially improved from 1.44MPa${\cdot}m^{1/2}$ and 270Mpa for YZ8Y to 3.62MPa${\cdot}m^{1/2}$ and 447MPa respectively, but electrical conductivity at $^{\circ}$C in air was decreased from 0.126 to 0.057${\Omega}^{-1}cm^{-1}$. It seemed due to the presence of small amount of tetragonal zirconia. But when 21.58wt% Yag(8.0mol% $Y_2O_3$) was added, fracture toughness of 2.93MPa${\cdot}m^{1/2}$ and flexural strength of 388MPa were obtained with electrical conductivity of ${\Omega}^{-1}cm^{-1}$.

• The Journal of Korean Academy of Prosthodontics
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• v.57 no.3
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• pp.263-270
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• 2019

Current trends in restorative dentistry focus on improving the esthetics and keeping the sound dental tissues as long as possible. The aims of this case report were to describe the successful outcome of cubic-phase zirconia laminate veneers for a patient with isolated microdontia by using a digital workflow, and to describe their clinical implications. A 15-year-old female who had isolated microdontia in combination with spacing visited Ajou University Dental Hospital for esthetic treatment. In this case, 6 maxillary anterior teeth were restored with cubic-phase zirconia laminate veneers without tooth structure removal by using a digital impression, computer-aided design (CAD) software, and computer-aided manufacturing (CAM) procedures. At 6-month follow-up, no distinct mechanical and biological complications were detected and the prostheses exhibited satisfactory esthetics and functions. Due to its favorable tissue responses and enhanced translucency, cubic-phase zirconia can be a suitable strategy for a noninvasive esthetic approach.

• Journal of the Korean Ceramic Society
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• v.29 no.7
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• pp.544-550
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• 1992

Zirconia gel fibers could be made by drawing from polyester sol containing zirconyl oxychloride during the reaction between ethylen glycol and citric acid. In this case, the critical mole ratio of zirconyl oxychloride to citric acid was about 4 and by adding CaCl2 and calcining the gel fiber in the air, cubic stabilized zirconia fibers having much micropores at surface could be obtained.

• Journal of the Mineralogical Society of Korea
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• v.14 no.2
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• pp.99-110
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• 2001

A gem-quality yttria-stabilized zirconium oxide crystals were synthesized by the skull-melting method, using the RF electrical apparatus. Principal raw materials used were $ZrO_2$and 25 wt.% $Y_2O_3$as stabilizer and 0.03~0.05 wt.% $Nd_2O_3$decolorizing agent were added to it. The single crystals were approximately 20$\times$63 mm in size with chemical composition $Zr_{0.73}$ $Y_{0.27}$ $O_{1.87}$ . The crystals are isotropic with no appreciable anisotropism under a polarizing microscope. Their refractive indices are in the range of 2.15~2.18, specific gravity 5.85, Mohs' hardness 8~8.5, and reflectivity 13.47%. The zirconia crystals were confirmed to have cubic structure with Face-centered lattice(Z=4), space group Fm3m ($CaF_2$-type structure) and unit cell parameters are a=5.157 $\AA$. The optimal growing conditions for yttria-stabilized zirconia are 50 kW, 2.94 MHz in power and to use a crucible with 105 mm $\times$ 135 mm in size. When the lowering speed of the crucible was set 16mm/hr gave the best yield, 42%. Since the refractive index(2.15~2.18) of cubic zirconia is smaller than that of diamond, the angle between crown and pavilion should be fashioned to make it smaller than $40.5^{\circ}$ to show the maximum brilliancy and fire.

• Journal of Dental Rehabilitation and Applied Science
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• v.34 no.4
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• pp.306-316
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• 2018

Monolithic zirconia has been widely used in fixed partial dentures due to high strength and fracture toughness. Nevertheless, the usage of monolithic zirconia in anterior restoration was limited because of opacity. Recently, esthetic monolithic zirconia blocks are developed by improving translucency and using various shading systems. Manufacturer introduces 3M $Lava^{TM}$ Esthetic with increased cubic phase and fluorescent ingredients is more esthetic than previous monolithic zirconia. This case report describes favorable anterior restorations using translucent monolithic zirconia.

• Journal of the Korean Ceramic Society
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• v.29 no.11
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• pp.851-854
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• 1992

It was grown ZrO2:10 mol% Y2O3 single crystals doped with 1 wt% of rare earth metal ion (Ce, Pr, Nd, Er, Eu) by Skull Method. Grown crystals showed Ce:orange-red, Pr:golden-yellow, Nd:lilac, Er:pink, Eu:light pink due to dopant effect. It was examined color centers in light absorption pattern of visible region (λ= 300~700 nm); in as grown samples, absorption by Ce4+, (Pr4+, Pr3+), Nd3+, Er3+, Eu3+ ions were important, and in samples after vacuum annealing, decrease of absorption by Pr4+ ion and increase of absorption by Pr3+ ion was important, and absorption by Ce3+, Eu2+ was important due to reduction of activator.

• Korean Journal of Materials Research
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• v.24 no.12
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• pp.677-681
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• 2014

To increase the mechanical property of zirconia, we have investigated the phase change and the resulting hardness of zirconia ceramics by hydroxyapatite (HA) powder bed sintering. It was observed using X-ray diffraction that the cubic zirconia phase, which has a higher hardness value than that of the tetragonal phase, was obtained at the surface of 3 mol% $Y_2O_3$ doped tetragonal zirconia polycrystal (3Y-TZP) ceramics during the sintering process; in our experimental conditions, the phase change at the surface increased as the sintering time increased. We believe that the observed crystalline phase change originated from the decomposition of HA and the diffusion of CaO, as follows. CaO, which was derived from the decomposition of HA at high temperature ($1400^{\circ}C$), diffused into the surface of 3Y-TZP and acted as a stabilizer. As a result, the Vickers hardness value of the treated specimens was higher than that of the non-treated specimen due to the formation of the cubic phase on the surface of 3Y-TZP.