title: Strength, toughness and aging stability of highly-translucent Y-TZP ceramics for dental restorations.
abstract: The aim was to evaluate the optical properties, mechanical properties and aging stability of yttria-stabilized zirconia with different compositions, highlighting the influence of the alumina addition, Y2O3content and La2O3doping on the translucency.
  
  
  
  Five different Y-TZP zirconia powders (3 commercially available and 2 experimentally modified) were sintered under the same conditions and characterized by X-ray diffraction with Rietveld analysis and scanning electron microscopy (SEM). Translucency (n=6/group) was measured with a color meter, allowing to calculate the translucency parameter (TP) and the contrast ratio (CR). Mechanical properties were appraised with four-point bending strength (n=10), single edge V-notched beam (SEVNB) fracture toughness (n=8) and Vickers hardness (n=10). The aging stability was evaluated by measuring the tetragonal to monoclinic transformation (n=3) after accelerated hydrothermal aging in steam at 134°C, and the transformation curves were fitted by the Mehl-Avrami-Johnson (MAJ) equation. Data were analyzed by one-way ANOVA, followed by Tukey's HSD test (α=0.05).
  
  
  
  Lowering the alumina content below 0.25wt.% avoided the formation of alumina particles and therefore increased the translucency of 3Y-TZP ceramics, but the hydrothermal aging stability was reduced. A higher yttria content (5mol%) introduced about 50% cubic zirconia phase and gave rise to the most translucent and aging-resistant Y-TZP ceramics, but the fracture toughness and strength were considerably sacrificed. 0.2mol% La2O3doping of 3Y-TZP tailored the grain boundary chemistry and significantly improved the aging resistance and translucency. Although the translucency improvement by La2O3doping was less effective than for introducing a substantial amount of cubic zirconia, this strategy was able to maintain the mechanical properties of typical 3Y-TZP ceramics.
  
  
  
  Three different approaches were compared to improve the translucency of 3Y-TZP ceramics.
authors.affiliation: KU Leuven, Department of Materials Engineering, Kasteelpark Arenberg 44, Belgium. Electronic address: fei.zhang@kuleuven.be.
authors.forename: Fei
authors.initials: F
authors.lastname: Zhang
authors.affiliation: KU Leuven BIOMAT, Department of Oral Health Sciences, KU Leuven & Dentistry, University Hospitals Leuven, Belgium; Gerodontology and Oral Rehabilitation, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo, Tokyo 113-8510, Japan.
authors.forename: Masanao
authors.initials: M
authors.lastname: Inokoshi
authors.affiliation: Electron Microscopy for Materials Science (EMAT), University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
authors.forename: Maria
authors.initials: M
authors.lastname: Batuk
authors.affiliation: Electron Microscopy for Materials Science (EMAT), University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
authors.forename: Joke
authors.initials: J
authors.lastname: Hadermann
authors.affiliation: KU Leuven BIOMAT, Department of Oral Health Sciences, KU Leuven & Dentistry, University Hospitals Leuven, Belgium.
authors.forename: Ignace
authors.initials: I
authors.lastname: Naert
authors.affiliation: KU Leuven BIOMAT, Department of Oral Health Sciences, KU Leuven & Dentistry, University Hospitals Leuven, Belgium.
authors.forename: Bart
authors.initials: B
authors.lastname: Van Meerbeek
authors.affiliation: KU Leuven, Department of Materials Engineering, Kasteelpark Arenberg 44, Belgium.
authors.forename: Jef
authors.initials: J
authors.lastname: Vleugels
mesh_terms: D002516:Ceramics; D003764:Dental Materials; D003799:Dental Stress Analysis; D006244:Hardness; D008422:Materials Testing; D014961:X-Ray Diffraction; D015019:Yttrium; D015040:Zirconium
chemical_list: D003764:Dental Materials; C499362:yttria stabilized tetragonal zirconia; D015019:Yttrium; D015040:Zirconium
keywords: Aging; Dental restorations; Mechanical properties; Translucency; Yttria; Zirconia