title: The strength of sintered and adhesively bonded zirconia/veneer-ceramic bilayers.
abstract: OBJECTIVE
  Recently all-ceramic restorative systems have been introduced that use CAD/CAM technology to fabricate both the Y-TZP core and veneer-ceramic layers. The aim was to identify whether the CAD/CAM approach resulted in more favourable stressing patterns in the veneer-ceramic when compared with a conventionally sintered Y-TZP core/veneer-ceramic.
  
  
  METHODS
  Nominally identical Vita VM9 veneer-ceramic disc-shaped specimens (0.7mm thickness, 12mm diameter) were fabricated. 20 specimens received a surface coating of resin-cement (Panavia 21); 20 specimens were bonded with the resin-cement to fully sintered Y-TZP (YZ Vita Inceram Vita) discs (0.27mm thickness, 12mm diameter). A final series of 20 Y-TZP core/veneer-ceramic specimens were manufactured using a conventional sintering route. Biaxial flexure strength was determined in a ball-on-ring configuration and stress at the fracture origin calculated using multilayer closed-form analytical solutions. Fractography was undertaken using scanning electron microscopy. The experimental test was simulated using Finite Element Analysis. Group mean BFS were compared using a one-way ANOVA and post hoc Tukey tests at a 95% significance level.
  
  
  RESULTS
  Resin cement application resulted in significant strengthening of the veneer-ceramic and further significant strengthening of the veneer-ceramic (p<0.01) occurred following bonding to the Y-TZP core. The BFS calculated at the failure origin for conventionally sintered specimens was significantly reduced when compared with the adhesively bonded Y-TZP/veneer-ceramic.
  
  
  CONCLUSIONS
  Under the test conditions employed adhesive cementation between CAD/CAM produced Y-TZP/veneer-ceramic layers appears to offer the potential to induce more favourable stress states within the veneer-ceramic when compared with conventional sintered manufacturing routes.
  
  
  CONCLUSIONS
  The current investigation suggests that the stressing patterns that arise in all-ceramic restorations fabricated using CAD/CAM for both the core and veneer-ceramic layers differ from those that occur in conventionally sintered bilayer restorations. Further work is required to ascertain whether such differences will translate into improved clinical outcomes.
authors.affiliation: Biomaterials Unit, University of Birmingham, School of Dentistry, St. Chad's Queensway, Birmingham B4 6NN, UK; Dental Materials and Prosthodontics Unit, Sao Jose dos Campos Dental School, Institute of Technology and Science, SP, Brazil.
authors.forename: Anna Karina F
authors.initials: AK
authors.lastname: Costa
authors.affiliation: Dental Materials and Prosthodontics Unit, Sao Jose dos Campos Dental School, Institute of Technology and Science, SP, Brazil.
authors.forename: Alexandre Luiz S
authors.initials: AL
authors.lastname: Borges
authors.affiliation: Materials Science Unit, Dublin Dental University Hospital, Lincoln Place, Dublin 2, Ireland.
authors.forename: Garry James P
authors.initials: GJ
authors.lastname: Fleming
authors.affiliation: Biomaterials Unit, University of Birmingham, School of Dentistry, St. Chad's Queensway, Birmingham B4 6NN, UK. Electronic address: addisono@adf.bham.ac.uk.
authors.forename: Owen
authors.initials: O
authors.lastname: Addison
mesh_terms: D000134:Acid Etching, Dental / Q000379:methods; D000465:Algorithms; D000537:Aluminum Oxide / Q000737:chemistry; D017554:Carbon Compounds, Inorganic / Q000737:chemistry; D002484:Cementation / Q000379:methods; D002516:Ceramics / Q000737:chemistry*; D017076:Computer-Aided Design; D001840:Dental Bonding; D045662:Dental Etching / Q000379:methods; D003764:Dental Materials / Q000737:chemistry*; D003775:Dental Polishing / Q000379:methods; D003801:Dental Veneers; D055119:Elastic Modulus; D020342:Finite Element Analysis; D006358:Hot Temperature; D006801:Humans; D006858:Hydrofluoric Acid / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D010710:Phosphates / Q000737:chemistry; D018583:Pliability; D019279:Resin Cements / Q000737:chemistry; D012821:Silanes / Q000737:chemistry; D017655:Silicon Compounds / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: D017554:Carbon Compounds, Inorganic; D003764:Dental Materials; C093719:Panavia TPN-S; D010710:Phosphates; D019279:Resin Cements; D012821:Silanes; D017655:Silicon Compounds; C499362:yttria stabilized tetragonal zirconia; D015019:Yttrium; D015040:Zirconium; D000537:Aluminum Oxide; D006858:Hydrofluoric Acid; C022088:silicon carbide
keywords: Bi-axial flexure strength; CAD-CAM; FEA; Fractography; Fracture; Veneer-ceramic; Zirconia