title: Effect of autoclave induced low-temperature degradation on the adhesion energy between yttria-stabilized zirconia veneered with porcelain.
abstract: OBJECTIVE
  To investigate the effect of autoclave induced low-temperature degradation on the adhesion energy between yttria-stabilized zirconia veneered with porcelain.
  
  
  METHODS
  The strain energy release rate using a four-point bending stable fracture test was evaluated for two different porcelains [leucite containing (VM9) and glass (Zirox) porcelain] veneered to zirconia. Prior to veneering the zirconia had been subjected to 0 (control), 1, 5, 10 and 20 autoclave cycles. The specimens were manufactured to a total bi-layer dimension of 30 mm × 8 mm × 3 mm. Subsequent scanning electron microscopy/energy dispersive spectrometry, electron backscatter diffraction and X-ray diffraction analysis were performed to identify the phase transformation and fracture behavior.
  
  
  RESULTS
  The strain energy release rate for debonding of the VM9 specimens were significantly higher (p<0.05) compared to the Zirox specimens across all test groups. Increasing autoclave cycles lowered the strain energy release rate significantly (p<0.05) from 18.67 J/m(2) (control) to the lowest of 12.79 J/m(2) (cycle 10) for only the VM9 specimens. SEM analyses showed predominant cohesive fracture within the porcelain for all cycle groups. XRD analysis of the substrate prior to veneering confirmed a tetragonal to monoclinic phase transformation with increasing the number of autoclave cycles between 5 and 20. The monoclinic phase reverted back to tetragonal phase after undergoing conventional porcelain firing cycles. EBSD data showed significant changes of the grain size distribution between the control and autoclaved specimen (cycle 20).
  
  
  CONCLUSIONS
  Increasing autoclave cycles only significantly decreased the adhesion of the VM9 layered specimens. In addition, a conventional porcelain firing schedule completely reverted the monoclinic phase back to tetragonal.
authors.affiliation: Sir John Walsh Research Institute, University of Otago, Dunedin, New Zealand. Electronic address: lika6144@gmail.com.
authors.forename: Kai Chun
authors.initials: KC
authors.lastname: Li
authors.forename: J Neil
authors.initials: JN
authors.lastname: Waddell
authors.forename: David J
authors.initials: DJ
authors.lastname: Prior
authors.forename: Stephanie
authors.initials: S
authors.lastname: Ting
authors.forename: Liz
authors.initials: L
authors.lastname: Girvan
authors.forename: Ludwig Jansen
authors.initials: LJ
authors.lastname: van Vuuren
authors.forename: Michael V
authors.initials: MV
authors.lastname: Swain
mesh_terms: D003776:Dental Porcelain; D003801:Dental Veneers; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D013052:Spectrometry, X-Ray Emission; D013696:Temperature; D014961:X-Ray Diffraction; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003776:Dental Porcelain; D015019:Yttrium; D015040:Zirconium
keywords: Autoclave; Bond strength; EBSD; Electron backscatter diffraction; Four point bend; Fracture behavior; Strain energy release rate; Veneering porcelain; Zirconia