title: Fracture and Fatigue Resistance of Cemented versus Fused CAD-on Veneers over Customized Zirconia Implant Abutments.
abstract: OBJECTIVE
  To evaluate the fracture mechanics of cemented versus fused CAD-on veneers on customized zirconia implant abutments.
  
  
  METHODS
  Forty-five identical customized CAD/CAM zirconia implant abutments (0.5 mm thick) were prepared and seated on short titanium implant abutments (Ti base). A second scan was made to fabricate 45 CAD-on veneers (IPS Empress CAD, A2). Fifteen CAD-on veneers were cemented on the zirconia abutments (Panavia F2.0). Another 15 were fused to the zirconia abutments using low-fusing glass, while manually layered veneers served as control (n = 15). The restorations were subjected to artificial aging (3.2 million cycles between 5 and 10 kg in a water bath at 37°C) before being axially loaded to failure. Fractured specimens were examined using scanning electron microscopy to detect fracture origin, location, and size of critical crack. Stress at failure was calculated using fractography principles (alpha = 0.05).
  
  
  RESULTS
  Cemented CAD-on restorations demonstrated significantly higher (F = 72, p < 0.001) fracture load compared to fused CAD-on and manually layered restorations. Fractographic analysis of fractured specimens indicated that cemented CAD-on veneers failed due to radial cracks originating from the veneer/resin interface. Branching of the critical crack was observed in the bulk of the veneer. Fused CAD-on veneers demonstrated cohesive fracture originating at the thickest part of the veneer ceramic, while manually layered veneers failed due to interfacial fracture at the zirconia/veneer interface.
  
  
  CONCLUSIONS
  Within the limitations of this study, cemented CAD-on veneers on customized zirconia implant abutments demonstrated higher fracture than fused and manually layered veneers.
authors.affiliation: Department of Fixed Prosthodontics, Future University, Cairo, Egypt.
authors.forename: Shereen Ahmed
authors.initials: SA
authors.lastname: Nossair
authors.affiliation: Department of Fixed Prosthodontics, Future University, Cairo, Egypt.
authors.forename: Moustafa N
authors.initials: MN
authors.lastname: Aboushelib
authors.affiliation: Fixed Prosthodontics Department, Ain Shams University, Cairo, Egypt.
authors.forename: Tarek Salah
authors.initials: TS
authors.lastname: Morsi
keywords: CAD-on veneers; fatigue; fractography; fracture mechanics