title: The influence of grain size on low-temperature degradation of dental zirconia.
abstract: The purpose of this study was to evaluate the influence of grain size and air abrasion on low-temperature degradation (LTD) of yttria stabilized tetragonal zirconia polycrystalline (Y-TZP). Disc-shaped specimens were sintered at 1350, 1450, and 1600°C. Air abrasion was performed with different abrasive particles. The specimens were stored for 2 h at 134°C under 2.3 bar water vapor pressure. All specimens were characterized by X-ray powder diffraction analysis (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM). Y-TZP sintered at a temperature of 1350°C did not undergo the t-m phase transformation during accelerated aging. The diffusion-controlled t-m phase transformation initiated with the specimens sintered at 1450°C. This transformation was remarkable for the specimens sintered at 1600°C. X-ray photoelectron spectroscopy (XPS) measurements did not confirm the generation of Zr-OH and Y-OH bonds. No increase of yttrium concentration on the grain boundaries of Y-TZP was detected, which could be responsible for the destabilization of dental zirconia ceramics. A slight increase of diffusion-controlled t-m phase transformations was observed for all abraded specimens sintered at 1350 and 1450°C. The size of abrasive particles did not play a crucial role on LTD of Y-TZP. The retardation of diffusion-controlled t-m phase transformation was evident for all abraded specimens sintered at 1600°C by comparison to non-abraded specimens.
  
  
  CONCLUSIONS
  The LTD of Y-TZP can be suppressed when the sintering temperature is set between 1350 and 1450°C.
authors: Clinic of Fixed and Removable Prosthodontics and Dental Material Science, Center of Dental Medicine, University of Zürich, Zurich, Switzerland. lubica.hallmann@zzm.uzh.ch.
authors: Lubica
authors: L
authors: Hallmann
authors: Albert
authors: A
authors: Mehl
authors: Peter
authors: P
authors: Ulmer
authors: Eric
authors: E
authors: Reusser
authors: Johannes
authors: J
authors: Stadler
authors: Renato
authors: R
authors: Zenobi
authors: Bogna
authors: B
authors: Stawarczyk
authors: Mutlu
authors: M
authors: Özcan
authors: Christoph H F
authors: CH
authors: Hämmerle
mesh_terms: D015921:Dental Implants; D006358:Hot Temperature; D008422:Materials Testing; D014961:X-Ray Diffraction; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: D015921:Dental Implants; D015019:Yttrium; D015040:Zirconium; C028541:zirconium oxide