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: The results demonstrate that roughness alone cannot be used for ensuring a long-term stability of biomedical grade zirconia, and the variation of ageing sensitivity is indeed related indirectly to the surface roughness via the induced surface stress state.
269 citations
"State of the art of zirconia for de..." refers background in this paper
...[6] Deville S, Chevalier J, Gremillard L....
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...However, due to the metastability of tetragonal zirconia, stress-generating surface treatments such as grinding or sandblasting are liable to trigger the t → m transformation with the associated volume increase leading to the formation of surface compressive stresses, thereby increasing the flexural strength but also altering the phase integrity of the material and increasing the susceptibility to aging [6]....
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267 citations
TL;DR: Dental ceramics are presented within a simplifying framework allowing for understanding of their composition and development, and the meaning of strength and details of the fracture process are explored.
257 citations
Additional excerpts
...[63] Kelly JR....
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TL;DR: The combination of the reduced surface roughness and the formation of a surface layer of compressive stress as a result of the alumina abrasion regimes investigated increased the reliability of the bi-axial flexure strength.
229 citations
Additional excerpts
...[61] Curtis AR, Wright AJ, Fleming GJP....
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TL;DR: In this paper, the surface integrity of advanced ceramics, including alumina, alumina-titania, and yttria partially stabilized tetragonal zirconia, were studied under high speed deep grinding conditions.
Abstract: Machining characteristics and surface integrity of advanced ceramics, including alumina, alumina-titania, and yttria partially stabilized tetragonal zirconia, were studied under high speed deep grinding conditions. Material removal mechanisms involved in the grinding processes were explored. The material removal in the grinding of alumina and alumina-titania was dominated by grain dislodgement or lateral cracking along grain boundaries. The removal for zirconia was via both local micro fracture and ductile cutting. It was found that under a feed rate of 500 mm/min and for all the wheel speeds used, an increase in the wheel depth of cut (DOC) from 0.1-2 mm slightly improved the ground surface finish, but greatly prolonged the wheel life. This increase did not deepen the subsurface damage layer for the alumina and alumina-titania, but resulted in a slightly deeper damage layer for the zirconia.
199 citations
"State of the art of zirconia for de..." refers background in this paper
...Huang studied the effect of grinding speed on the type of machining damage in Y-TZP and reported both brittle and ductile removal modes at high speed with less subsurface damage [27,59]....
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