title: The effects of viscoelastic parameters on residual stress development in a zirconia/glass bilayer dental ceramic.
abstract: OBJECTIVE
  The aim of this study was to test the hypothesis that the residual stresses in a zirconia-based bilayer dental composite system can be tailored through heat treatment above and below the glass transition temperature of glass veneers.
  
  
  METHODS
  Ceramic bilayer disc specimens were prepared from a zirconia core and a glass veneer. Each bilayer ceramic group was heat treated 40 degrees C below, 20 degrees C and 40 degrees C above and at the glass transition temperature of the glass veneer, and cooled using a fast or a slow cooling rate. Specimens were tested for flexure strength using a biaxial bending fixture. Residual stresses were calculated using a fracture mechanics approach.
  
  
  RESULTS
  Heat treatments produced significant differences (p < or =0.05) between the mean flexural strengths of the heat treatment groups when the specimens were cooled using a fast cooling rate. However, there was not a significant difference (p >0.05) between the mean flexural strengths of the heat treatment groups when a slow cooling rate was used. Fractures initiated from the veneer surfaces of the specimens.
  
  
  CONCLUSIONS
  Heat treatment above and below the glass transition temperature of the veneer layer, and the cooling rate have a significant effect on the flexural strength of the bilayer ceramic laminates. The existence of residual compressive stress is the most likely reason for the observed strength increases. Residual stresses can be modified using the elastic-viscoelastic relaxation behavior of a glass veneer.
authors.affiliation: Department of Restorative Dentistry, Division of Dental Biomaterials, Indiana University School of Dentistry, Indianapolis, Indiana 46202, USA. btaskona@iupui.edu
authors.forename: Burak
authors.initials: B
authors.lastname: Taskonak
authors.forename: Gilberto A
authors.initials: GA
authors.lastname: Borges
authors.forename: John J
authors.initials: JJ
authors.lastname: Mecholsky
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Anusavice
authors.forename: B Keith
authors.initials: BK
authors.lastname: Moore
authors.forename: Jiahau
authors.initials: J
authors.lastname: Yan
mesh_terms: D000465:Algorithms; D002516:Ceramics / Q000737:chemistry*; D003461:Crystallography; D003764:Dental Materials / Q000737:chemistry*; D004548:Elasticity; D005898:Glass / Q000737:chemistry*; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D019563:Mechanics; D018583:Pliability; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D044366:Transition Temperature; D014783:Viscosity; D014961:X-Ray Diffraction; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003764:Dental Materials; C499362:yttria stabilized tetragonal zirconia; D015019:Yttrium; D015040:Zirconium; C028541:zirconium oxide