• The Journal of the Korean dental association
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• v.49 no.5
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• pp.265-278
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• 2011

The introduction of zirconia-based materials to the dental field broadened the design and application limits of, all-ceramic restorations. Most ceramic restorations are adhesively luted to the prepared tooth, however, resin bonding to zirconia components is less reliable than those to other dental ceramic systems. It is important for high retention, prevention of microleakage, and increased fracture resistance, that bonding techniques be improved for zirconia systems. Strong resin bonding relies on micromechanical interlocking and adhesive chemical bonding to the ceramic surface, requiring surface roughening for mechanical bonding and surface activation for chemical adhesion. In many cases, high strength ceramic restorations do not require adhesive bonding to tooth structure and can be placed using conventional cements which rely only on micromechanical retention. However, resin bonding is desirable in some clinical situations. In addition, it is likely that strong chemical adhesion would lead to enhanced long-term fracture and fatigue resistance in the oral environment.

• Electrical & Electronic Materials
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• v.10 no.6
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• pp.562-569
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• 1997

The resonance characteristics on vibration mode of a transverse type ceramic resonator and the output voltage characteristics of a piezoelectric ceramic transformer are discussed in the effects of partial electrode arrangement (one sided, centered and both sided). A resonance characteristics of resonator depended strongly on both a vibration mode and a electrode structure because of a strain distribution. The maximum resonance current of a piezoelectric ceramic transformer [PCT] with partial centered electrode appeared in λ/2 mode, and that of a PCT with partial both sided electrode appeared in 3λ/2 mode. But the maximum output voltage of those samples appeared in λ/2 mode. In the PCT with partial both sided electrode, the ration of output voltage to input current was highest out of all samples and the poling voltage was a half times of 깬두 type transformer.

• Journal of Dental Rehabilitation and Applied Science
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• v.22 no.2
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• pp.149-159
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• 2006

Statement of problem. Porcelain repair mainly involves replacement with composite resin, but the bond strength between composite resin and all-ceramic coping materials has not been studies extensively. Purpose. The objective of this study was to investigate the influence of composite resin and ceramic etching pattern on shear bond strength of Empress2 ceramic and observe the change of microstructure of ceramic according to etching methods. Material and methods. Eighty-five cylinder shape ceramic specimens (diameter 5mm, IPS Empress 2 core materials) embeded by acrylic resin were used for this study. The ceramic were specimens divided into sixteen experimental groups with 5 specimens in each group and were etched with phosphoric acid(37%, 65%) & hydrofluoric acid (4%, 9%) according to different etching times(30s, 60s, 120s 180s). All etched ceramic surfaces were examined morphologically using SEM(scanning electron microscopy). Etched surfaces of ceramic specimens were coated with silane (Monobond-S) & adhesive(Heliobond) and built up composite resin using Teflon mold. Accomplished specimens were tested under shear loading until fracture on universal testing machine at a crosshead speed 1mm/min; the maximum load at fracture(kg) was recorded. Shear bond strength data were analyzed with one way ANOVA and Duncan tests.(P<.05) Results. Maximum shear bond strength was $30.07{\pm}2.41(kg)$ when the ceramic was etched with 4% hydrofluoric acid at 120s. No significant difference was found between phosphoric etchant group and control group with respect to shear bond strength. Conclusion. Empress 2 ceramic surface was not etched by phosphoric acid, but etched by hydrofluoric acid.

• The Journal of Advanced Prosthodontics
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• v.12 no.6
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• pp.329-337
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• 2020

PURPOSE. To verify the influence of computer-aided design/computer-aided manufacturing (CAD/CAM) implant-supported prostheses manufactured with cobalt-chromium (Co-Cr) and zirconia (Zr), and whether ceramic application, spark erosion, and simulation of masticatory cycles modify biomechanical parameters (marginal fit, screw-loosening torque, and strain) on the implant-supported system. MATERIALS AND METHODS. Ten full-arch fixed frameworks were manufactured by a CAD/CAM milling system with Co-Cr and Zr (n=5/group). The marginal fit between the abutment and frameworks was measured as stated by single-screw test. Screw-loosening torque evaluated screw stability, and strain analysis was explored on the implant-supported system. All analyses were performed at 3 distinct times: after framework manufacturing; after ceramic application in both materials' frameworks; and after the spark erosion in Co-Cr frameworks. Afterward, stability analysis was re-evaluated after 106 mechanical cycles (2 Hz/150-N) for both materials. Statistical analyses were performed by Kruskal-Wallis and Dunn tests (α=.05). RESULTS. No difference between the two materials was found for marginal fit, screwloosening torque, and strain after framework manufacturing (P>.05). Ceramic application did not affect the variables (P>.05). Spark erosion optimized marginal fit and strain medians for Co-Cr frameworks (P<.05). Screw-loosening torque was significantly reduced by masticatory simulation (P<.05) regardless of the framework materials. CONCLUSION. Co-Cr and Zr frameworks presented similar biomechanical behavior. Ceramic application had no effect on the biomechanical behavior of either material. Spark erosion was an effective technique to improve Co-Cr biomechanical behavior on the implant-supported system. Screw-loosening torque was reduced for both materials after masticatory simulation.

• Journal of the Korean Academy of Esthetic Dentistry
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• v.23 no.2
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• pp.86-94
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• 2014

In recent years, perhaps the biggest driver in new material development is the desire to improve crown and bridge esthetics compared to the traditional PFM or all-metal restorations. As such, zirconia, leucite-containing glass ceramic and lithium disilicate glass ceramic have become prominent in the dental practice. Each material type performs differently regarding strength, toughness, ease of machining and the final preparation of the material prior to placement. For example, glass ceramic are typically weaker materials which limits its use to single-unit restorations. On the other hand, zirconia has a high fracture toughness which enables multi-unit restorations. This material requires a long sintering procedure which excludes its use for fast chair side production. Developed hybrid material of CAD/CAM is contained nano ceramic elements. This new material, called a Resin Nano Ceramic is unique in durability and function. The material is not a resin or composite. It is also not a pure ceramic. The material is a mixture of both and consists of ceramic. Like a composite, the material is not brittle and is fracture resistant. Like a glass ceramic, the material has excellent polish retention for lasting esthetics. The material is easily machined chair side or in a dental lab, polishes quickly to an esthetic finish and if necessary, can be useful restoratives.

• Journal of the Korean Ceramic Society
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• v.56 no.5
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• pp.489-496
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• 2019

Cement-based thermal insulation material was manufactured using OPC, lime, anhydrite, and CSA cement in this study. The morphology and physical properties of the material were analyzed using XRD. All samples had ettringite, Ca(OH)₂, and CaCO₃ crystals. The XRD peak intensity of the ettringite and Ca(OH)₂ slightly increased with an increase in curing time from 3 to 7 days. The compressive strength values at 28 days of specimens 1-8 were in the range of 0.25-0.32 MPa, and the compressive strength values of specimens 3-8 were > 0.3 MPa. The coefficients of correlation between compressive strength and apparent gravity at 7 days and those between compressive strength and ettringite/Ca(OH)₂ XRD peak intensity at 28 days were above 0.8. That is, the compressive strength exhibited an influence on apparent gravity at 7 days and on hydrate at 28 days. The thermal conductivity of all specimens was 0.041-0.045 W/mK, and the highest value of thermal conductivity was shown by specimen 5. The coefficient of correlation between apparent gravity and thermal conductivity was 0.84. It was concluded that control of raw materials and hydrates must be considered for manufacturing of insulation materials. The cement-based thermal insulation material in this study could be used in construction fields.

• Journal of the Korean Ceramic Society
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• v.52 no.1
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• pp.33-40
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• 2015

Onggi, described as a 'breathing' type of pottery' has significantly influenced the traditional food culture of Korea. It is known that Onggi is an optimal type of storage for fermented foods such as soy sauce, salted seafood, and Kimchi, as air or liquid can penetrate through the body of this material. These foods gain flavor due to the breeding of aerobic bacteria at the beginning of the fermentation process. In this study, Onggi materials from five regions, Gangjin, Yeoju, Ulsan, Yesan, and Jeju, were collected and analyzed to determine their chemical and physical properties before and after sintering. The differences in the raw materials of other mining regions are examined in terms of their chemical and mineralogical compositions, specific surface area, particle size, and particle distribution. Among them, the Gangjin raw material has the greatest mean particle size of $92.29{\mu}m$, as well as the widest particle size distribution. Differences in the levels of $SiO_2$ and $Fe_2O_3$ are shown among Onggi raw materials. However, the crystalline phases formed after sintering are identical, except for the Jeju samples. At all sintering temperatures tested here, Gangjin Onggi showed the greatest porosity, leading to complete air permeation through the body within 90 minutes. These results taken together indicate that air permeation is strongly related to the pore structures in the Onggi body. This is assumed to affect the fermentation behavior.

• The Journal of Advanced Prosthodontics
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• v.5 no.2
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• pp.179-186
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• 2013

PURPOSE. One of the most important factors in evaluating the quality of fixed dental prostheses (FDPs) is their gap. The purpose of this study was to compare the marginal and internal gap of two different metal-ceramic crowns, casting and selective laser sintering (SLS), before and after porcelain firing. Furthermore, this study evaluated whether metal-ceramic crowns made using the SLS have the same clinical acceptability as crowns made by the traditional casting. MATERIALS AND METHODS. The 10 study models were produced using stone. The 20 specimens were produced using the casting and the SLS methods; 10 samples were made in each group. After the core gap measurements, 10 metal-ceramic crowns in each group were finished using the conventional technique of firing porcelain. The gap of the metal-ceramic crowns was measured. The marginal and internal gaps were measured by two-dimensional and three-dimensional replica techniques, respectively. The Wilcoxon signed-rank test, the Wilcoxon rank-sum test and nonparametric ANCOVA were used for statistical analysis (${\alpha}$=.05). RESULTS. In both groups, the gap increased after completion of the metal-ceramic crown compared to the core. In all measured areas, the gap of the metal cores and metal-ceramic crowns produced by the SLS was greater than that of the metal cores and metal-ceramic crowns produced using the casting. Statistically significant differences were found between cast and SLS (metal cores and metal-ceramic crown). CONCLUSION. Although the gap of the FDPs produced by the SLS was greater than that of the FDPs produced by the conventional casting in all measured areas, none exceeded the clinically acceptable range.

• Journal of the Korean Ceramic Society
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• v.50 no.3
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• pp.206-211
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• 2013

The effect of a $WO_3$ or $Ga_2O_3$ addition on the densification, phase evolution, optical reflectance, and elastic and dielectric properties of $Y_2O_3$-doped AlN ceramics sintered at $1800^{\circ}C$ for 3 h is investigated. The investigated compositions of the additives are 4.5 wt% $Y_2O_3$ (YA), 3.5 wt% $Y_2O_3$-1.0 wt% $Ga_2O_3$ (YGA), and 3.5 wt% $Y_2O_3$-1.0 wt% $WO_3$ (YWA). $YAlO_3$ and $Y_4Al_2O_9$ form as the secondary phases in all of the investigated compositions, whereas $W_2B$ appears additionally in the YWA. In the YGA, Ga is detected in the AlN grains, indicating that the dissolution of $Ga_2O_3$ into the AlN lattice occurs. The addition of $WO_3$ blackens the specimen more significantly than that of $Ga_2O_3$ does. In all of the investigated specimens, the linear shrinkage and the apparent density are above 20 percent and in the range of 3.34-3.37 $g/cm^3$, respectively. The elastic modulus, Poisson's ratio, the dielectric constant, and the dielectric loss are in the ranges of 335-368 GPa, 0.146-0.237, 8.60-8.63, $2.65-3.95{\times}10^{-3}$, respectively. The sinterability and the properties of $Y_2O_3$-doped AlN ceramics are not much altered by the addition of $WO_3$ or $Ga_2O_3$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.6
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• pp.356-360
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• 2017

We investigated the phase evolution, microstructure, and microwave dielectric properties of Na- and Zr-doped $Ba(Mg_{0.5}W_{0.5})O_3$ [i.e., ($Ba_{1-2x}Na_{2x})(Mg_{0.5-x}Zr_xW_{0.5})O_3$] ceramics. $BaWO_4$ as a secondary phase was observed in all compositions, and it increased as the dopant concentration increased. All specimens revealed a dense microstructure. For the composition of x=0.01, polyhedral grains were observed. As the dopant concentration increased, the densification and the grain growth were promoted by a liquid phase. The quality factor($Q{\times}f_0$) decreased remarkably, whereas the dielectric constant (${\varepsilon}_r$) tended to decrease as the dopant concentration increased. The dielectric constant, quality factor, and temperature coefficient of the resonant frequency of the composition of x=0.01 sintered at $1,700^{\circ}C$ for 1 h were 18.6, 216,275 GHz, and $-22.0ppm/^{\circ}C$, respectively.