title: Effect of thermal expansion mismatch on the Y-TZP/veneer interfacial adhesion determined by strain energy release rate.
abstract: OBJECTIVE
  The aim of this study was to assess the effect of differences in the thermal expansion behaviour of veneering ceramics on the adhesion to Y-TZP, using a fracture mechanics approach.
  
  
  METHODS
  Seven veneering ceramics (VM7, VM9, VM13, Lava Ceram, Zirox, Triceram, Allux) and one Y-TZP ceramic were investigated. Thermal expansion coefficients and glass transition temperatures were determined to calculate residual stresses (σ(R), MPa) between core and veneer. Subsequently, the veneering ceramics were fired onto rectangular shaped zirconia specimens, ground flat and notched on the veneering porcelain side. Then specimens were loaded in a four-point bending test and load-displacement curves were recorded. The critical load to induce stable crack extension at the adhesion interface was evaluated to calculate the strain energy release rate (G, J/m(2)) for each system.
  
  
  RESULTS
  Residual stresses ranged from -48.3±1.5MPa (VM7) to 36.1±4.8MPa (VM13) with significant differences between all groups (p<0.05). The strain energy release rate of the Y-TZP/veneer specimens ranged from 8.2±1.7J/m(2) (Lava Ceram) to 17.1±2.8J/m(2) (VM9). Values for G could not be obtained with the VM7, Allux and VM13 specimens, due to spontaneous debonding or unstable crack growth. Except for Triceram and Zirox specimens, strain energy release rate was significantly different between all groups (p<0.05).
  
  
  CONCLUSIONS
  Thermal residual stresses and strain energy release rates were correlated. Slight compressive stresses in the region of -20MPa were beneficial for the Y-TZP/veneer interfacial adhesion. Stresses higher or lower than this value exhibited decreased adhesion.
authors.affiliation: Department of Operative Dentistry and Periodontology, Assmanshauser Strasse 4-6, Charité Berlin, Berlin, Germany.
authors.forename: Gerd
authors.initials: G
authors.lastname: Göstemeyer
authors.forename: Michael
authors.initials: M
authors.lastname: Jendras
authors.forename: Lothar
authors.initials: L
authors.lastname: Borchers
authors.forename: Friedrich-Wilhelm
authors.initials: FW
authors.lastname: Bach
authors.forename: Meike
authors.initials: M
authors.lastname: Stiesch
authors.forename: Philipp
authors.initials: P
authors.lastname: Kohorst
mesh_terms: D002516:Ceramics / Q000592:standards*; D001840:Dental Bonding; D003799:Dental Stress Analysis; D003801:Dental Veneers; D006358:Hot Temperature; D013314:Stress, Mechanical; D015040:Zirconium
chemical_list: D015040:Zirconium; C028541:zirconium oxide