• 대한치과의사협회지
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• 제51권1호
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• pp.6-11
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• 2013

Dental ceramics is well known to have excellent esthetics, biocompatibility as well as high compressive strength. However, the fragility of ceramics against tensile and shear loads leading to the delayed fracture of micro crack on ceramic surface and the backwardness of ceramic fabrication technique limit the usage of ceramic materials in dentistry. Among all ceramic materials, zirconia has been introduced to overcome the drawback of conventional dental ceramics in the field of dentistry due to the nature of zirconia featuring proper opalescence and high fracture toughness. Also, novel manufacturing techniques enable ceramic materials to prepare high esthetic anterior and posterior all ceramic system. In this paper, it is introduced and discussed that novel techniques characterizing the bond strength between zirconia core and veneering ceramics and analyzing the fluorescence of dental ceramics in order to overcome the gap between the results of basic research and the feasibility of the results in the field of dental clinics.

• 대한치과의사협회지
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• 제49권5호
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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.

• 한국세라믹학회지
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• 제46권4호
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• pp.379-384
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• 2009

Zirconia is widely used for structural materials in machinery due to its superior properties, such as high strength, high hardness, and high toughness. Zirconia generally has ivory or white color. Therefore many studies are performed for diversification of zirconia color, in order to be widely uitilized for decoration and machine parts which need distincfive color. In this study, graphite is used to prevent structural defect, to maintain superior properties, and to develop black color of zirconia by impregnation method. As specimen was impregnated at $1600^{\circ}C$ for 2 h, bending strength is 1221 MPa, density is $6.01\;g/cm^3$, hardness is 10.1 GPa, absorption coefficient is 0%, transmittance is Fail, chromaticity is 54. The results indicate that black zirconia has enough properties to be adopted as mechanical parts. Optimum impregnation time is 2 h for various observations.

• 대한치과기공학회지
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• 제38권3호
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• pp.135-142
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• 2016

Purpose: The aim of this research was to evaluate the influence of different surface treatments on the shear bond strength of zirconia ceramic to composite resin. Methods: Seventy two cylinder-shape (diameter: 5 mm; height: 12 mm) blocks of experimental industrially manufactured Y-TZP ceramic were abraded with $125{\mu}m\;Al_2O_3$ particles and randomly divided into 4 groups. All the materials were categorized as group Gc(control group - composite resin veneering on zirconia surface), Gr - composite resin veneering after surface treatment of Rocatec system (3M ESPE, Seefeld, Germany) group; Gz - composite resin veneering after surface treatment of Zirconia primer (Z-primer, Bisco, U.S.A) group; Gm - composite resin veneering after surface treatment of zirconia primer (Monobond plus, ivoclar vivadent AG, Liechtenstein) group. Two different zirconia primers and Rocatec system were used to zirconia cylinders (n=16) onto the zirconia surface. Zirconia specimens, polished and roughened, were pretreated and composite bilayer cylinders bonded using conventional adhesive techniques. Results: Shear bond strengths were analyzed using single-factor ANOVA(p<0.05). Bond strength values achieved after airbone particle abrasion and zirconia surface pre-treatments(p<0.05). Conclusion: Shear bond strength tests denmonstrated that zirconia primer is a viable method to improved bond strength between zirconia ceramic core and veneering composites.

• 대한치과기공학회지
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• 제29권2호
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• pp.79-85
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• 2007

In this study, We tried to find out the fracture strength of zirconia coping all ceramic crown and collarless porcelain fused gold alloy crown as the compared group. Each of the collarless porcelain fused gold crown and zirconia all ceramic crown has been produced specimen 10 each. And after pasting them on the steel jig, it had load given at porcelain incisal edge by 130$^{\circ}$ and measured fracture strength by Universal Testing Machine and then We have results from that. 1. The average value of fracture strength suggested 950.49 N at collarless porcelain fused gold alloy crown, 656.81 N at zirconia coping all ceramic crown. 2. Fractured pattern showed that the whole of labial part was exposed in collarless porcelain fused gold crown, but porcelain of margin part did not show fracture in advance. In the practice, the concern that collarless might cause fracture strength to be weaken does not matter, we concluded zirconia all ceramic crown made fracture that only a part of labial porcelain was fractured. The combination of zirconia all ceramic crown and turned out to be excellent.

• 대한치과기공학회지
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• 제33권1호
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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.

• The Journal of Advanced Prosthodontics
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• 제7권5호
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• pp.368-374
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• 2015

PURPOSE. The aim of the study was to evaluate the effect of abutment shade, ceramic thickness, and coping type on the final shade of zirconia all-ceramic restorations. MATERIALS AND METHODS. Three different types of disk-shaped zirconia coping specimens (Lava, Cercon, Zirkonzahn: ${\phi}10mm{\times}0.4mm$) were fabricated and veneered with IPS e.max Press Ceram (shade A2), for total thicknesses of 1 and 1.5 mm. A total of sixty zirconia restoration specimens were divided into six groups based on their coping types and thicknesses. The abutment specimens (${\phi}10mm{\times}7mm$) were prepared with gold alloy, base metal (nickel-chromium) alloy, and four different shades (A1, A2, A3, A4) of composite resins. The average $L^*$, $a^*$, $b^*$ values of the zirconia specimens on the six abutment specimens were measured with a dental colorimeter, and the statistical significance in the effects of three variables was analyzed by using repeated measures analysis of variance (${\alpha}$=.05).The average shade difference (${\Delta}E$) values of the zirconia specimens between the A2 composite resin abutment and other abutments were also evaluated. RESULTS. The effects of zirconia specimen thickness (P<.001), abutment shade (P<.001), and type of zirconia copings (P<.003) on the final shade of the zirconia restorations were significant. The average ${\Delta}E$ value of Lava specimens (1 mm) between the A2 composite resin and gold alloy abutments was higher (close to the acceptability threshold of 5.5 ${\Delta}E$) than th ose between the A2 composite resin and other abutments. CONCLUSION. This in-vitro study demonstrated that abutment shade, ceramic thickness, and coping type affected the resulting shade of zirconia restorations.

• 대한치과기공학회지
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• 제33권3호
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• pp.193-202
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• 2011

Purpose: The aim of this study was to evaluate the effect of pre-treatment of core and hydrothermal treatment on the bond strength and flexural strength of ceramic veneered zirconia. Methods: 3Y-TZP specimens(KaVo Zr, $25mm{\times}3mm{\times}1mm$)were prepared by five pre-treatment methods and divided into seven groups including control two groups, subsequently the specimens veneered with the E-MAX ceram according to manufacturer's information(total specimen thickness 1.5mm). Two groups from ceramic-zirconia specimens(n=105, n=15 per group)were assigned into two experimental fatigue conditions, namely storage in an autoclave at $134^{\circ}C$ for 5h, thermo-cycling(3,000cycles, between 5 and $55^{\circ}C$, dwell time 45s, transfer time 2s). A flexural strength test was performed in a universal testing machine(crosshead speed: 0.5mm/min). Data were statistically analyzed using one-way ANOVA and Tukey's test(${\alpha}$=0.05). Results: The ceramic-zirconia bond strength value for liner application group(LLW, $27.3{\pm}3.8$) were significantly lower than those of the pre-treatment groups($30.72{\pm}5.3$). The ceramic-zirconia bond strength and zirconia flexural strength was not affected by thermo-cycling(p>0.05), whereas it was affected by storage in an autoclave at $134^{\circ}C$ for 5h(p<0.05). Conclusion: The results indicated that the ceramic-zirconia bond strength and zirconia flexural strength was affected by low temperature degradation.

• 한국세라믹학회지
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• 제27권2호
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• pp.256-264
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• 1990

Cordierite(2MgO$.$2Al2O3$.$5SiO2) was known to display low thermal expansions over wide temperature ranges, but showed poor mechanical strength. The present studies have been concerned with the sintering of cordierite based ceramics containing pure or stabilized zirconia. The crystallographic and microstructural results were not affected by the fact whether added zirconia was stabilized or not. As the contents of zirconia were increased, M.O.R., KIC, bulk densities were increased but the thermal expansion coefficients were decreased.

• 대한치과기공학회지
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• 제42권4호
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• pp.307-312
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• 2020

Application of ceramic materials for fabrication of dental restoration materials has been a focus of interest in the field of esthetic dentistry. The ceramic materials of choice are glass ceramics, spinel, alumina, and zirconia. The development of yttrium tetragonal zirconia polycrystal (YTZP)-based systems is a recent addition to all-ceramic systems that have high strength and are used for crowns and fixed partial dentures. Computer-aided design/computer-aided manufacturing (CAD/CAM)-produced, YTZP-based systems are popular with respect to their esthetic appeal for use in stress-bearing regions. The highly esthetic nature of zirconia and its superior physical properties and biocompatibility have enabled the development of restorative systems that meet the demands of today's patients. Many in vitro trials have been performed on the use of zirconia; however, relatively fewer long-term clinical studies have been published on this subject. The use of zirconia frameworks for long-span fixed partial dentures is currently being evaluated; in the future, more in vivo research and long-term clinical studies are required to provide scientific evidence for drawing solid guidelines. Further clinical and in vitro studies are required to obtain data regarding the long-term clinical use of zirconia-based restorations.