title: Influence of zirconia framework thickness on residual stress profile in veneering ceramic: measurement by hole-drilling.
abstract: OBJECTIVE
  Framework design is reported to influence chipping in zirconia-based restorations, which is an important cause of failure of such restorations. Residual stress profile in the veneering ceramic after the manufacturing process is an important predictive factor of the mechanical behavior of the material. The objective of this study is to investigate the influence of framework thickness on the stress profile measured in zirconia-based structures.
  
  
  METHODS
  The stress profile was measured with the hole-drilling method in bilayered disc samples of 20mm diameter with a 1.5 mm thick veneering ceramic layer. Six different framework thicknesses from 0.5 mm to 3 mm were studied. Two different cooling procedures were also investigated.
  
  
  RESULTS
  Compressive stresses were observed in the surface, and tensile stresses in the depth of most of the samples. The slow cooling procedure was found to promote the development of interior tensile stresses, except for the sample with a 3mm thick framework. With the tempering procedure, samples with a 1.5 mm thick framework exhibited the most favorable stress profile, while thicker and thinner frameworks exhibited respectively in surface or interior tensile stresses.
  
  
  CONCLUSIONS
  The measurements performed highlight the importance of framework thickness, which determine the nature of stresses and can explain clinical failures encountered, especially with thin frameworks. The adequate ratio between veneering ceramic and zirconia is hard to define, restricting the range of indications of zirconia-based restorations until a better understanding of such a delicate veneering process is achieved.
authors.affiliation: Department of Fixed Prosthodontics, Institute of Dentistry, University of Liège Hospital (ULg CHU), Liège, Belgium. a.mainjot@chu.ulg.ac.be
authors.forename: Amélie K
authors.initials: AK
authors.lastname: Mainjot
authors.forename: Gary S
authors.initials: GS
authors.lastname: Schajer
authors.forename: Alain J
authors.initials: AJ
authors.lastname: Vanheusden
authors.forename: Michaël J
authors.initials: MJ
authors.lastname: Sadoun
mesh_terms: D003080:Cold Temperature; D019245:Compressive Strength; D003776:Dental Porcelain; D003799:Dental Stress Analysis; D003801:Dental Veneers; D003779:Denture Design; D003830:Denture, Partial, Fixed; D008422:Materials Testing / Q000379:methods*; D044367:Phase Transition; D013718:Tensile Strength; D015019:Yttrium; D015040:Zirconium
chemical_list: C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; D015019:Yttrium; D015040:Zirconium