title: Making yttria-stabilized tetragonal zirconia translucent.
abstract: OBJECTIVE
  The aim of this study was to provide a design guideline for developing tetragonal yttria-stabilized zirconia with improved translucency.
  
  
  METHODS
  The translucency, the in-line transmission in particular, of 3mol.% yttria-stabilized tetragonal zirconia (3Y-TZP) has been examined using the Rayleigh scattering model. The theory predicts that the in-line transmission of 3Y-TZP can be related to its thickness with grain size and birefringence the governing parameters. To achieve a threshold value of translucency, the critical grain size of 3Y-TZP was predicted for various thicknesses (0.3-2.0mm). The threshold value was defined by a measured average in-line transmission value of a suite of dental porcelains with a common thickness of 1mm. Our theoretical predictions were calibrated with one of the very few experimental data available in the literature.
  
  
  RESULTS
  For a dense, high-purity zirconia, its in-line transmission increased with decreasing grain size and thickness. To achieve a translucency similar to that of dental porcelains, a nanocyrstalline 3Y-TZP structure was necessitated, due primarily to its large birefringence and high refractive index. Such a grain size dependence became more pronounced as the 3Y-TZP thickness increased. For example, at a thickness of 1.3mm, the mean grain size of a translucent 3Y-TZP should be 82nm. At 1.5mm and 2mm thicknesses, the mean grain size needed to be 77nm and 70nm, respectively.
  
  
  CONCLUSIONS
  A promising future for zirconia restorations, with combined translucency and mechanical properties, can be realized by reducing its grain size.
authors.affiliation: Department of Biomaterials and Biomimetics, New York University College of Dentistry, 345 East 24th Street, New York, NY 10010, USA. Electronic address: yz21@nyu.edu.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D008956:Models, Chemical; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: D015019:Yttrium; D015040:Zirconium; C028541:zirconium oxide
keywords: Grain size; Light scattering; Microstructure; Optical birefringence; Translucency; Zirconia (Y-TZP)