title: Phase transformation of dental zirconia following artificial aging.
abstract: OBJECTIVE
  Low-temperature degradation (LTD) of yttria-stabilized zirconia can produce increased surface roughness with a concomitant decrease in strength. This study determined the effectiveness of artificial aging (prolonged boiling/autoclaving) to induce LTD of Y-TZP (yttria-tetragonal zirconia-polycrystals) and used artificial aging for transformation depth progression analyses. The null hypothesis is aging techniques tested produce the same amount of transformation, transformation is not time/temperature dependent and LTD causes a constant transformation throughout the Y-TZP samples.
  
  
  METHODS
  Dental-grade Y-TZP samples were randomly divided into nine subgroups (n = 5): as received, 3.5 and 7 day boiling, 1 bar autoclave (1, 3, 5 h), and 2 bar autoclave (1, 3, 5 h). A 4-h boil treatment (n = 2) was performed post-experiment for completion of data. Transformation was measured using traditional X-ray diffraction and low-angle X-ray diffraction.
  
  
  RESULTS
  The fraction of t → m transformation increased with aging time. The 3.5 day boil and 2 bar 5 h autoclave produced similar transformation results, while the 7 day boiling treatment revealed the greatest transformation. The surface layer of the aged specimen underwent the most transformation while all samples displayed decreasing transformation with depth.
  
  
  CONCLUSIONS
  Surface transformation was evident, which can lead to rougher surfaces and increased wear of opposing dentition/materials. Therefore, wear studies addressing LTD of Y-TZP are needed utilizing accelerated aging.
authors.affiliation: Department of Biomaterials, School of Dentistry, University of Alabama at Birmingham, Birmingham, Alabama.|Department of Materials Science and Engineering, University of Alabama at Birmingham, Birmingham, Alabama.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Lucas
authors.affiliation: Department of Biomaterials, School of Dentistry, University of Alabama at Birmingham, Birmingham, Alabama.
authors.forename: Nathaniel C
authors.initials: NC
authors.lastname: Lawson
authors.affiliation: Department of Materials Science and Engineering, University of Alabama at Birmingham, Birmingham, Alabama.
authors.forename: Gregg M
authors.initials: GM
authors.lastname: Janowski
authors.affiliation: Department of Biomaterials, School of Dentistry, University of Alabama at Birmingham, Birmingham, Alabama.
authors.forename: John O
authors.initials: JO
authors.lastname: Burgess
mesh_terms: D017266:Dental Prosthesis; D006801:Humans; D044367:Phase Transition; D013499:Surface Properties; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: C499362:yttria stabilized tetragonal zirconia; D015019:Yttrium; D015040:Zirconium
keywords: X-ray diffraction; phase transformation; yttria stabilized; zirconia