State of the art of zirconia for dental applications
TL;DR: The two main processing techniques, soft and hard machining, are assessed in the light of their possible clinical implications and consequences on the long-term performance of zirconia.
About: This article is published in Dental Materials.The article was published on 2008-03-01. It has received 1696 citations till now.
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TL;DR: In this article, it is shown that many of these attractive features of zirconia, especially fracture toughness and strength, are compromised after prolonged exposure to water vapor at intermediate temperatures (∼30°-300°C).
Abstract: Zirconia ceramics have found broad applications in a variety of energy and biomedical applications because of their unusual combination of strength, fracture toughness, ionic conductivity, and low thermal conductivity. These attractive characteristics are largely associated with the stabilization of the tetragonal and cubic phases through alloying with aliovalent ions. The large concentration of vacancies introduced to charge compensate of the aliovalent alloying is responsible for both the exceptionally high ionic conductivity and the unusually low, and temperature independent, thermal conductivity. The high fracture toughness exhibited by many of zirconia ceramics is attributed to the constraint of the tetragonal-to-monoclinic phase transformation and its release during crack propagation. In other zirconia ceramics containing the tetragonal phase, the high fracture toughness is associated with ferroelastic domain switching. However, many of these attractive features of zirconia, especially fracture toughness and strength, are compromised after prolonged exposure to water vapor at intermediate temperatures (∼30°–300°C) in a process referred to as low-temperature degradation (LTD), and initially identified over two decades ago. This is particularly so for zirconia in biomedical applications, such as hip implants and dental restorations. Less well substantiated is the possibility that the same process can also occur in zirconia used in other applications, for instance, zirconia thermal barrier coatings after long exposure at high temperature. Based on experience with the failure of zirconia femoral heads, as well as studies of LTD, it is shown that many of the problems of LTD can be mitigated by the appropriate choice of alloying and/or process control.
1,132 citations
TL;DR: A critical survey of all experimental data about the low temperature degradation of zirconia due to the tetragonal-to-monoclinic transformation shows that the main factors affecting the aging phenomenon are the stabilizer type and content, the residual stress and the grain size.
534 citations
TL;DR: It is demonstrated that highly polished zirconia yielded lower antagonist wear compared with porcelains, and combined application of silica coating and/or silane coupler, and 10-methacryloyloxydecyl dihydrogen phosphate is currently one of the most reliable bonding systems for zirConia.
529 citations
Cites background from "State of the art of zirconia for de..."
...Zirconia-based ceramics, especially Y-TZP, are clinically available as an alternative to metal frameworks for FDPs [16,17]....
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TL;DR: The progressive development of currently available and next-generation zirconias is reviewed, representing a concerted drive toward greater translucency while preserving adequate strength and toughness.
Abstract: Zirconias, the strongest of the dental ceramics, are increasingly being fabricated in monolithic form for a range of clinical applications. Y-TZP (yttria-stabilized tetragonal zirconia polycrystal) is the most widely used variant. However, current Y-TZP ceramics on the market lack the aesthetics of competitive glass-ceramics and are therefore somewhat restricted in the anterior region. This article reviews the progressive development of currently available and next-generation zirconias, representing a concerted drive toward greater translucency while preserving adequate strength and toughness. Limitations of efforts directed toward this end are examined, such as reducing the content of light-scattering alumina sintering aid or incorporating a component of optically isotropic cubic phase into the tetragonal structure. The latest fabrication routes based on refined starting powders and dopants, with innovative sintering protocols and associated surface treatments, are described. The need to understand the several, often complex, mechanisms of long-term failure in relation to routine laboratory test data is presented as a vital step in bridging the gaps among material scientist, dental manufacturer, and clinical provider.
477 citations
TL;DR: The central argument of this study is that residual stresses developed during the preparation of all-ceramic crowns and fixed partial dentures coupled with contact-induced cracking are the origin of the excessive chipping observed in clinical applications.
456 citations
Cites background from "State of the art of zirconia for de..."
...This combination has very attractive aesthetic and biocompatibility properties in addition to its high strength and fracture toughness [2]....
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References
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TL;DR: In this article, it was shown that partially stabilized zirconia containing homogeneously nucleated precipitates of tetragonal ZrO/sub 2/ of low solute content in a cubic matrix of high solute contents can change to the stable monoclinic structure within the stress field of the crack.
Abstract: Recent discovery is announced that partially stabilized zirconia containing homogeneously nucleated precipitates of tetragonal ZrO/sub 2/ of low solute content in a cubic matrix of high solute content, the primary contribution to the toughness is associated with particles within a ''transformation zone'' adjacent to a propagating crack. These particles change to the stable monoclinic structure within the stress field of the crack. (GHT)
386 citations
"State of the art of zirconia for de..." refers background in this paper
...The toughness is therefore enhanced by microcracking [5,46]....
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TL;DR: Since a special Y-TZP grade containing a small amount of alumina exhibited the highest damage tolerance and superior stability in an acidic environment, this material shows considerable promise for dental applications.
Abstract: This work was undertaken to evaluate the effects of dental grinding and sandblasting on the biaxial flexural strength and Weibull modulus of various Y-TZP ceramics containing 3 mol% yttria. In addition, the susceptibility of pristine and mechanically treated materials to low-temperature degradation under the conditions adopted for testing the chemical solubility of dental ceramics was investigated. The results revealed that surface grinding and sandblasting exhibit a counteracting effect on the strength of Y-TZP ceramics. Dental grinding lowered the mean strength and Weibull modulus, whereas sandblasting provided a powerful method for strengthening, but at the expense of somewhat lower reliability. The finest-grained material exhibited the highest strength after sintering, but it was less damage tolerant than tougher, coarse-grained materials. Upon extraction with the acetic acid solution and the ammonia solution, a significant amount of tetragonal zirconia had transformed to monoclinic, but extensive microcracking and attendant strength degradation had not yet occurred. Standard grade Y-TZP ceramics are more resistant in an alkaline than in an acidic environment, and there was a strong grain-size dependence of the diffusion-controlled transformation. Since a special Y-TZP grade containing a small amount of alumina exhibited the highest damage tolerance and superior stability in an acidic environment, this material shows considerable promise for dental applications.
385 citations
"State of the art of zirconia for de..." refers background in this paper
...Several authors have reported that annealing at 900 ◦C for 1 h or relatively short heat treatments in the temperature range 900–1000 ◦C for 1 min induce the reverse transformation from monoclinic to tetragonal [32,33]....
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...[32] Kosmac T, Oblak C, Jevnikar P, Funduk N, Marion L....
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TL;DR: In this article, the detrimental aging phenomenon observed in ZrO2-Y2O3 materials was investigated with respect to the gaseous aging environment and the Y 2O3 and SiO2 content of the material and it was shown that the aging phenomenon is caused by water vapor and that intergranular silicate glassy phases play no significant role.
Abstract: The detrimental aging phenomenon observed in ZrO2-Y2O3 materials, which causes tetragonal ZrO2 to transform to its monoclinic structure at temperatures between 150 and 400°C, was investigated with respect to the gaseous aging environment and the Y2O3 and SiO2 content of the material. It is shown that the aging phenomenon is caused by water vapor and that inter-granular silicate glassy phases play no significant role. Transmission electron microscopy of thin foils, before and after aging, showed that the water vapor reacted with yttrium in the ZrO2 to produce clusters of small (20 to 50 nm) crystallites of α-Y(OH)3. It is hypothesized that this reaction produces a monoclinic nucleus (depleted of Y2O3) on the surface of an exposed tetragonal grain. Monoclinic nuclei greater than a critical size grow spontaneously to transform the tetragonal grain. If the transformed grain is greater than a critical size, it produces a microcrack which exposes subsurface tetragonal grains to the aging phenomenon and results in catastrophic degradation. Degradation can be avoided if the grain size is less than the critical size required for microcracking.
360 citations
"State of the art of zirconia for de..." refers background in this paper
...The low temperature degradation (LTD) of zirconia is a well-documented phenomenon, exacerbated notably by the presence of water [7–12]....
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...[10] Lange FF, Dunlop GL, Davis BI....
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TL;DR: FPDs made of pre-sintered HIP ZrO2 core material veneered with a compatible ceramic is an acceptable alternative in the fabrication of FPDs with the extensions investigated in this study, within the limitations of this 2-year clinical follow-up study.
Abstract: The aim of the study was to investigate whether the properties of a pre-sintered, hot iso-static post-compacted ( HIP) ZrO2 are adequate for use in three-five-unit fixed partial dentures (FPDs) and to evaluate the clinical results. Twenty three five-unit FPDs were fabricated for 18 patients on a total of 56 abutments. They were all made on abutments cut with a shoulder preparation and cemented with a zinc phosphate cement. They were clinically followed for 24 months. After 24 months all FPDs were still in use without any fractures or clinical wear but in three cases (15%) minor chip-of fractures were observed. Marginal integrity was rated excellent at 45 abutments and acceptable at 11. Within the limitations of this 2-year clinical follow-up study, FPDs made of pre-sintered HIP ZrO2 core material veneered with a compatible ceramic is an acceptable alternative in the fabrication of FPDs with the extensions investigated in this study. Special attention, however, must be paid to designing the core for an occlusal shape that provides sufficient support for the veneer. (Less)
340 citations
TL;DR: In this article, the fracture toughness of dense Ce-TZP ceramics containing about 7 to 16 mol% CeO2 was evaluated using fine powders prepared by the hydrolysis technique.
Abstract: Dense Ce-TZP ceramics containing about 7 to 16 mol% CeO2 were fabricated using fine powders prepared by the hydrolysis technique. The mechanical properties of these ceramics were evaluated. The bending strength of sintered bodies with 10 to 12 mol% CeO2 content and small grain-size was about 800 MPa. Fracture toughness was measured by two different methods; a micro-indentation technique and the chevron notched beam technique. A high fracture toughness was obtained for sintered bodies with 7 to 10% CeO2 content and large grain-size. Fracture toughness and hardness were dependent on CeO2 content and grain-size. These mechanical properties are discussed on the basis of the stability of the metastable tetragonal phase depending on CeO2 content and grain-size.
338 citations