• Journal of the Korean Ceramic Society
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• v.50 no.5
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• pp.348-352
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• 2013

The evaluation of plasma resistance and the characteristics of yttria ceramics fabricated by calcination yttria as a starting material without dopants under an oxidation atmosphere was investigated. Regardless of the starting materials, as-received, and calcined yttria powder, XRD patterns showed that all samples have $Y_2O_3$ phase. The three cycling process inhibited a large grain, which occurs frequently during the yttria sintering, and a high density ceramic with a homogeneous grain size was obtained. The grain size of the sintered ceramic was affected by the starting powders. The smaller the grain size, the larger were the Young's modulus and KIC. Compared to $Al_2O_3$ and $ZrO_2$ ceramics, yttria ceramics showed a 3 times larger plasma resistance and a 1.4~2.2 times lower weight loss during the plasma etching test, respectively.

• Journal of Technologic Dentistry
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• v.33 no.1
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• pp.15-23
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• 2011

Purpose: Thy yttria tetragonal zirconia polycrystalline(Y-TZP) is a good structural ceramic for dental restoration. But it have a problem that delamination of veneering ceramic from the Y-TZP core materials. The problem generally occur at the interface, thus this study was conducted to evaluate the interface of Y-TZP using scanning electron microscopy(SEM). Methods: To investigate this aspect, high-resolution SEM observations were made of polished and etched (HF content gel) cross-sections of the interface area. Dry and moist veneering porcelain powders were built up on the zirconia base. Results: The extent of this surface faceting is dependent upon the moisture content of the porcelain powder and the firing temperature. More moisture and higher final heating temperature accelerates the observed faceting of the Y-TZP grains at the interface to the veneering ceramic. Conclusion: These changes of the Y-TZP grains indicate that destabilization of the tetragonal phase of zirconia occurs at the interface during veneering with ceramic. It may result in a reduction of the stability of the zirconia and interface.

• Hip & pelvis
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• v.34 no.2
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• pp.115-121
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• 2022

Purpose: The purpose of this study was to evaluate the wear and survival rates of third-generation ceramic heads on a conventional ultra-high molecular weight polyethylene liner. Materials and Methods: A total of 160 hips (147 patients with a mean age of 55.9 years) who underwent total hip arthroplasty using the third-generation ceramic head on a conventional polyethylene liner from March 1998 to August 2003 were reviewed retrospectively. Evaluation of the wear rate for 56 hips (49 patients) followed-up for at least 15 years was performed using the PolyWare program version 8 (Draftware Developers, USA). The Kaplan-Meier survivorship was also evaluated. Results: Linear wear and volumetric wear rates were 0.11±0.47 mm/year and 32.75±24.50 mm³/year, respectively. Nine revisions were performed during the follow-up period because of cup or stem loosening. The Kaplan-Meier survival rate, using cup revision or total revision total hip arthroplasty (THA) as the endpoint of analysis, was 93.7% at 15 years and 73.6% at 20 years. Conclusion: Because all revisions were performed between 15 and 20 years in our study, surgeons should pay greater attention to patients who underwent THA with ceramic-on-polyethylene bearing from 15 years postoperatively. Contemporary alumina ceramic on highly cross-linked polyethylene could certainly be a good alternative bearing couple providing better longevity.

• The Journal of Korean Academy of Prosthodontics
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• v.42 no.2
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• pp.125-132
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• 2004

Statements of problem: All ceramic fixed partial denture cores can be made by the slip casting method and the advanced alumina tape method. The fracture resistance of these core connector areas is relatively low. Purpose: The purpose of this study is to standardize the appropriate volumetric figure and location of the connectors in the alumina core fabricated in alumina tape to be used in fixed partial dentures by way of topology optimization. Material and method: A maxillary anterior three-unit bridge alumina core with teeth form and surrounding periodontal apparatus model was used to ultimately design the most structurally rigid form of the connector. Loadings from a $0^{\circ}$, $45^{\circ}$ and $60^{\circ}$ to the axis of each tooth were applied and analyzed with the 3-D finite element analysis method. Using the results from these experiments, the topology optimization was applied and the optimal reinforcement layout of connector was obtained and the detail shape in the fixed partial denture core was designed. Results: The modified prosthesis with the form of a bulk in the lower lingual surface of the connector in the event, reduced the stress concentration up to 20% in the 3-D FEA. Conclusion: The formation of a bulk in the lower lingual connector area of an alumina core for a fixed partial denture decreases the stress to a clinically favorable measure but does not harm the esthetic point of view. This result illustrates the possibility of clinical application of the modified form designed by the topology optimization method.

• The Journal of Korean Academy of Prosthodontics
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• v.32 no.2
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• pp.195-211
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• 1994

The purpose of this study was to evaluate the fracture resistance of the four kinds of dental porcelains for the all-ceramic crown(Vita In-Ceram, Vita Hi-Ceram, IPS-Empress, Vitadur-N) and one kind for the metal-ceramic non(Vita VMK 68) was used as the control group. In order to determine the fracture resistance, the hi-axial flexure strength was measured at a crosshead speed of 0.5mm/min, and the Vickers hadrness was measured at an indentation load of 1kg for 20 seconds. The results obtained were summarized as follows ; 1. The maximum Weibull modulus of 24.61 for Vitadur-N and the minimum one of 852 for IPS-Empress were observed ; the maximum characteristic strength of 353.26MPa for Vita In-Ceram and the minimum that of 63.20MPa for Vitadur-N were also observed. 2. The maximum mean bi-axial flexure strength of 339.12MPa for Vita In-Ceram and thd minimum one of 61.99MPa for Vitadur-N were calculated. Results of the Scheffe test indicated that the statistically significant difference(P<0.05) existed between Vita In-Ceram or Vita Hi-Ceram and the others ; also between IPS-Empress and Vitadur-N. 3. The maximum mean hardness of $980.55kg/mm^2$ for Vita VMK 68 appeared. Results of the Scheffe test indicated that statistically significant difference(P<0.05) existed between Vita In-Ceram or Vita Hi-Ceram and the others ; also between IPS-Empress and Vita VMK 68.

• The Journal of Advanced Prosthodontics
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• v.5 no.2
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• pp.92-97
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• 2013

PURPOSE. All-ceramic crowns are subject to fracture during function. To minimize this common clinical complication, zirconium oxide has been used as the framework for all-ceramic crowns. The aim of this study was to compare the fracture strengths of two computer-aided design/computer-aided manufacturing (CAD/CAM) zirconia crown systems: Lava and Digident. MATERIALS AND METHODS. Twenty Lava CAD/CAM zirconia crowns and twenty Digident CAD/CAM zirconia crowns were fabricated. A metal die was also duplicated from the original prepared tooth for fracture testing. A universal testing machine was used to determine the fracture strength of the crowns. RESULTS. The mean fracture strengths were as follows: $54.9{\pm}15.6$ N for the Lava CAD/CAM zirconia crowns and $87.0{\pm}16.0$ N for the Digident CAD/CAM zirconia crowns. The difference between the mean fracture strengths of the Lava and Digident crowns was statistically significant (P<.001). Lava CAD/CAM zirconia crowns showed a complete fracture of both the veneering porcelain and the core whereas the Digident CAD/CAM zirconia crowns showed fracture only of the veneering porcelain. CONCLUSION. The fracture strengths of CAD/CAM zirconia crowns differ depending on the compatibility of the core material and the veneering porcelain.

• Journal of the Korean Academy of Esthetic Dentistry
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• v.13 no.1
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• pp.31-39
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• 2004

For the prosthodontic results which are compatible with esthetics to be fulfilled, the first prerequisite would be periodontal intervention and stability, the second one may be functional competency and the ultimate goal should be ascribed to esthetic considerations. Other words, esthetic dentistry is a whole entity which encompasses the biological stability of the periodontium, physical accuracy of the prosthodontic structure and finally, the beauty which can be found in natural dentition. It also implies the harmonized lip line which reveals the well-balanced tooth morphology and health gum profiles (Red-White Esthetics). Largely, there lie some differences in the input system of the 3-dimentional data from the prepared abutments between respective computer-assisted systems available now. But the manufacturing systems (CAM) are very similar between them, to say, comprise numeric control systems with whole 3-dimensional milling units according to the restorations to be made. Now the author is going to present CAD/CAM Zirconia All Ceramic Restoration on the topics for the Red-White Esthetics, periodontal control and maintenance, treatment for the discolored teeth, post & core build-up works for the devitalized teeth, characteristics of the Zirconium oxide All Ceramics, fabrication procedures, clinical considerations and its application to diverse clinical situations.

• Journal of Technologic Dentistry
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• v.10 no.1
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• pp.177-183
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• 1988

This paper aims to examine ceramic shade prescriptions for work authorizations in all its aspectclincal information, recording information, technical considerations, extended application, practical applications. The results are as follows : 1. The basic application provides essential data for ceramic veneer fabrication. 2.Three-dimensional information divides the space for body and enamel components. 3. The second body shade selection improves shade matching in the middle one-third of the tooth and enhences the appearance of the enamel component. 4. Ceramists are encouraged to recognize the influence each component has upon the total shade composition. 5. A format is established for recording clinical information. 6. The use of available ceramic systems is seemingly unlimited. The method presented provides flexisility for recording the most detailed shade information in simple graphic and verbal terms. 7. Technical simplification is a by-product of complete, precise work information.

• Journal of the Korean Ceramic Society
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• v.56 no.6
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• pp.566-576
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• 2019

In this work, we investigated kaolinite raw materials from China, Vietnam, and Seongju (Korea) used for the manufacture of porcelain products in Korea. According to chemical analysis results, for the kaolinites from Seongju, more feldspar components containing CaO, K₂O, and Na₂O are found than in those from China or Vietnam, of which the composition is close to that of pure kaolinite. Through X-ray Rietveld quantitative analysis, kaolinite and muscovite are found to be the main phases for all the raw materials. Halloysite, quartz, gibbsite, and andesine are found at more than 5% for KM-85 (China), LKC-60 (Vietnam), KC-009 (China), and WA (Seongju). Absorption rate is on order of LKC-60 < KC-009 < KM-85 < PA < WA, and the sample, sintered in reductive atmosphere, exhibits the lowest absorption rate. Comparing the color of the sintered samples, kaolinites of KM-85, LKC-60, and KC-009 (L^*: 94 - 97%) show higher whiteness value than those of WA and PA (L^*: 82 - 91%).

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.519-524
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• 2001

These days, $Al_[2}O_{3}$ ceramic use all over the industry because dynamic function and special properties to compare traditional material. But $Al_[2}O_{3}$ ceramic is high hardness and brittleness materials. For this reason, it is very difficult to process. Therefor, In this paper, it was investigated that laser process parameter, which can produce appropriate quality of $Al_[2}O_{3}$ ceramic microhole machining utilized Nd:YAG laser and Excimer laser.