Mechanical and optical properties evaluation of rapid sintered dental zirconia (original) (raw)
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Application of Zirconia in Dentistry: Biological, Mechanical and Optical Considerations
Advances in Ceramics - Electric and Magnetic Ceramics, Bioceramics, Ceramics and Environment, 2011
2. Structural bioceramics based in zirconia 2.1 Zirconia Zircon is a shiny gray-white metal, which may look blue-black when in powder form. Zirconia is an oxide which has a high tensile strength, high hardness and corrosion resistance. It is not found as a pure oxide in nature. The main sources of zirconium are zirconate (ZrO 2-SiO 2 , ZrSiO 4) and baddelyite (ZrO 2), and most of the material used is chemically extracted from these two minerals. The zirconate is more abundant, but less pure, requiring significant processing to get zirconia. (Picone & Maccauro, 1999). Baddelyite already contains levels of zirconia ranging from 96.5% to 98.5%. As this mineral shows significant levels, it is known as a source of extreme purity in obtaining zirconium metal and its compounds. Zirconium dioxide (ZrO 2) resulting from baddelyite, which is also known as www.intechopen.com Advances in Ceramics-Electric and Magnetic Ceramics, Bioceramics, Ceramics and Environment 398 zirconia, is a course oxide that presents a monoclinic crystal structure at room temperature. However, the powder can be purified and processed synthetically at high temperatures, forming a cubic structure called cubic zirconia. The resulting material is hard, optically flawless and translucent, usually used for making precious stones or gas sensors, P. ex. (Koutayas et al., 2009). 2.2 Phases of zirconia (monoclic, tetragonal and cubic) The spatial arrangement of the atoms in zirconia is characterized by distinct crystallographic structures, characterizing a property known as polymorphism. Its three phases, or crystal structures, are characterized by specific geometry and dimensional parameters: monoclinic, tetragonal and cubic. (Fig. 1a,b,c). Pure zirconia has a monoclinic structure at room temperature, which is stable up to 1170°C. Between this temperature and 2370°C, tetragonal zirconia is formed, while cubic zirconia is formed at temperatures above 2370°C. After processing, and depending on the cooling process, the tetragonal phase becomes monoclinic at about 970°C. Due to polymorphism, pure zirconia cannot be used at elevated temperatures due to a large volume change (3-5%) which occurs during cooling to the monoclinic phase. This change is sufficient to exceed the elastic and fracture limits, resulting in cracks and flaws in ceramics. (Denry & Kelly, 2008). The transformation of the tetragonal to monoclinic phases can be employed to improve the mechanical properties of zirconia, especially its tenacity. The mechanism involved is known as a booster from transformation. This transformation is martensitic in nature, therefore, a process that occurs by shear without diffusion, ie the atomic position change occurs abruptly at a speed close to the speed of sound propagation in solids. The reverse transition, ie the monoclinic > tetragonal transformation and occurs at approximately 1170° C, while the tetragonal > monoclinic transformation, which occurs during cooling, is observed between 850 and 1000°C, depending on the strain energy. Therefore, the manufacturing of components of pure zirconia is not possible due to spontaneous failure. The addition of stabilizing oxides is important because it allows the maintenance of the tetragonal form at room temperature. (Hannink et al., 2000). Different oxides, such as yttrium oxide (Y 2 O 3), calcium oxide (CaO) or magnesium oxide (MgO), can be added to zirconia to stabilize it, allowing the tetragonal form to exist at room temperature after sintering. The addition of varying amounts of stabilizers allows the formation of partially or fully stabilized zirconia which, when combined with changes in processes, may result in ceramics with exceptional properties such as high flexural strength and fracture toughness, high hardness, excellent chemical resistance and good conductivity ions. A fully stabilized zirconia is obtained by adding sufficient amounts of stabilizing oxides, such as 16mol% magnesia (MgO), 16mol% of limestone (CaO) or 8 mol% yttria (Y 2 O 3). Since the partial stabilization of zirconia is obtained with the same oxides, but in smaller amounts (eg 2 mol% to 3mol% yttria), a multiphase structure is created, which usually consists of tetragonal and cubic zirconia majority / monoclinic precipitated in small amounts. (Picone & Maccauro, 1999). The transformation of tetragonal zirconia into monoclinic is a phenomenon influenced by temperature, vapor, particle size, micro-and macrostructure of the material, and also by the concentration of stabilizing oxides. The critical particle size for the partially stabilized zirconia to be maintained in the tetragonal form at room temperature is 0.2µm to 1μm (for compositions ranging from 2% to 3 mol% yttria), because, under 0.2 micrometres, the transformation to the monoclinic phase is not possible. (Kelly & Denry, 2008). www.intechopen.com Application of Zirconia in Dentistry: Biological, Mechanical and Optical Considerations 399 2.2.1 Monoclinic zirconia The natural form of zirconia, known as baddelyite, contains approximately 2% HfO 2 (hafnium oxide), which is very similar to zirconia in structure and chemical properties. ZR 4 + ions have a coordination number of seven for the oxygen ions occupying tetrahedral interstices, with the average distance between the zirconia ion and three of the seven oxygen ions is 2.07Å. Since the average distance between the zirconium ion and four oxygen ions is 2.21Å, in the structure, one of the angles (134.3°) differs significantly from the tetrahedral value (109.5°). Thus, the structure of the oxygen ion is not planar and a curve occurs in the plane of the four oxygens, and the plane of three oxygens is completely erratic. (Hannink et al., 2000) 2.2.2 Tetragonal zirconia Zirconia in its tetragonal phase has the form of a straight prism with rectangular sides. Ions ZR 4 + have a coordination number of eight, where the shape once again appears distorted due to the fact that four oxygen ions are at a distance of 2.065Å in the form of a tetrahedron plan, and four others are at a distance of 2.455Å in a tetrahedron that is elongated and rotated 90°. (Vagkopoulou et al, 2009).
Zirconia Use in Dentistry - Manufacturing and Properties
Current Health Sciences Journal, 2019
Several types of metal-free ceramics have been developed to meet the patients demand for natural looking appearance restorations. Owing to their biocompatibility and good mechanical properties zirconia has been successfully used in recent years as a dental biomaterial. Due to its high opacity zirconia cores are generally covered with ceramic veneers that provide a more natural appearance but have frequent incidence of chipping. As an alternative to veneered zirconia full-contour zirconia restorations become more widely used nowadays. The paper reviews the current knowledge and scientific data of the zirconia use in dentistry in order to compare the zirconia based dental restorations with the metal-ceramic ones and also the two types of dental restoration based on zirconia, veneered or monolithic zirconia.
Three generations of zirconia: From veneered to monolithic. Part II
2017
This article presents the historical development of the different generations of zirconia and their range of indications, from veneered to monolithic zirconia restorations. While Part I concentrated on detailed information about the development of zirconia for dental use and the mechanical and optical properties, Part II deals with the resulting guidelines for working with the relevant generations by summarizing the correct cementation procedure. Furthermore, this part also focuses on translucency measurements for better characterization and understanding of the different materials. The results obtained from measuring light transmission and contrast ratio are compared and discussed in detail, with the aid of clinical photographs. Finally, the reader is given practice-relevant recommendations for different areas of clinical use of the zirconia generations along with advice on how to process them appropriately.
An Overview of Zirconia and its Application in Dentistry
Dental Journal of Advance Studies, 2016
To replace metallic dental prosthesis the structure of ceramics has been improved. Among in Ceramics Zirconia has come up in a big way because of its biological, mechanical and optical properties. It has adequate mechanical properties to be used in medical devices. With addition of yittrium trioxide properties of zirconia improved tremendously to be used in dentistry. This review article gives general properties as well as specific clinical guidelines for its use in dentistry.
Zirconia a Modern Ceramic Material in Dentistry - a Systematic Review
Among the dental ceramics, zirconia has emerged as a resourceful and promising material because of its biological, mechanical and optical properties, which has certainly accelerated its routine use in CAD/CAM technology for different types of prosthetic treatment. The zirconia systems currently available for use in dentistry include ceramics with a 90% or higher content zirconium dioxide, which is the yttrium, stabilized tetragonal Zirconia (Y-TZP) and glass infiltrated ceramics with 35% partially stabilized zirconia. Zirconia based restorations are quite versatile and can be used for crowns, bridges, implant abutments and fixtures and as post materials. This article reviews the unique property of zirconia and its wide application in dentistry, with more emphasis on prosthetic uses. Keywords: Zirconia, Esthetics, Restorations, Mechanical properties.
Journal of Prosthodontic Research, 2021
Purpose: This systematic review set out to investigate the influence of chemical composition and specimen thickness of monolithic zirconia on its optical and mechanical properties. Meta-analysis and meta-regression analyzed the effects of variations in percentages of yttrium, aluminum, and specimen thickness of monolithic zirconia. Study selection: The review followed recommendations put forward in the PRISMA checklist. An electronic search for relevant articles published up to October 2019 was conducted in the Pubmed, Cochrane, Scopus, Scielo, and Web of Science databases, with no language limits and articles published in the last 10 years. From 167 relevant articles; applying inclusion criteria based on the review's PICO question, 26 articles were selected for qualitative synthesis (systematic review) and 24 for quantitative synthesis (meta-analysis). Experimental in vitro studies published were selected and their quality was assessed using the modified Consort scale for in vitro studies of dental materials. Results: The variables yttrium, aluminum and thickness were analyzed in random effects models, observing high heterogeneity (>75%), and finding statistically significant influences on the properties of monolithic zirconia (p<0.05). Conclusions: Within the review's limitations, it may be concluded that variations in the percentage of yttrium and aluminum influence the optical and mechanical properties of monolithic zirconia, making it more or less esthetic and resistant in relation to each variable. The clinical implications of these findings can help select the most appropriate type of zirconia to meet the different clinical needs when restoring different regions (posterior or anterior).
Sintering Strategies for Dental Zirconia Ceramics: Slow Versus Rapid.
Purpose of Review Advances in zirconia ceramics have expanded their application in dentistry, necessitating faster delivery of zirconia-based restorations. With the introduction of high translucency grades of zirconia ceramics, the rapid sintering strategies that aim to reduce processing times can have a central impact on clinically relevant properties. The present review has surveyed the available literature evaluating the properties of rapidly sintered dental zirconia ceramics. Recent Findings Recent studies emphasize the evolution of sintering protocols for zirconia ceramics, especially highlighting differences between conventional sintering (CS) and rapid methods like speed (SS) and high-speed sintering (HSS). These modern rapid sintering techniques transform the microstructure of zirconia ceramics, impacting its translucency, flexural strength, and aging resistance. These properties exhibit variability based on zirconia type and chosen sintering process, with HSS showing particular promise. Summary Rapid sintering protocols offer efficient alternatives to traditional zirconia ceramic processing, with benefits in cost and time. Despite the recent findings, discrepancies persist within zirconia generations, calling for further standardization and investigation.
Development of Translucent Zirconia for Dental Crown Applications
Asian Journal of Scientific Research, 2015
Zirconia-based dental ceramic is widely used for crown restoration, because of its superior mechanical properties and favorable biocompatibility. However, yttria-stabilized tetragonal zirconia (3YSZ), which is used in most dental crown restorations, has low translucency. This characteristic is unfavorable and results in low aesthetic quality of dental restoration. In this study, translucent 3YSZ dental ceramics were fabricated using nano-sized powder (20 nm) and high-temperature sintering (1500°C). The green bodies were slip casted and consolidated with cold iso-static pressing to create compact bodies. During the slip casting process different amounts of dispersing agent Polyethyleneimine (PEI) (0.2, 0.4, 0.6 and 0.8 wt%), were used to prevent agglomerates and create homogeneous suspensions. A minute amount (0, 0.1, 0.2, 0.3 and 0.4 wt%) of alumina was added into the suspension as sintering aid. The translucency or light transmittance of 3YSZ specimens was measured by an ultraviolet-visible spectrometer. Results showed that the 3YSZ specimen with 0.4 wt% alumina and 0.4 wt% PEI exhibited the highest light transmittance. The specimen also had larger grain size, because of excessive grain growth. The Vickers hardness of the specimens was insignificantly affected by the amount of alumina and PEI addition.