title: The fracture resistance of a CAD/CAM Resin Nano Ceramic (RNC) and a CAD ceramic at different thicknesses.
abstract: OBJECTIVE
  This study aimed to investigate the influence of restoration thickness to the fracture resistance of adhesively bonded Lava™ Ultimate CAD/CAM, a Resin Nano Ceramic (RNC), and IPS e.max CAD ceramic.
  
  
  METHODS
  Polished Lava™ Ultimate CAD/CAM (Group L), sandblasted Lava™ Ultimate CAD/CAM (Group LS), and sandblasted IPS e.max CAD (Group ES) discs (n=8, Ø=10 mm) with a thickness of respectively 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, and 3.0 mm were cemented to corresponding epoxy supporting discs, achieving a final thickness of 3.5 mm. All the 120 specimens were loaded with a universal testing machine at a crosshead speed of 1 mm/min. The load (N) at failure was recorded as fracture resistance. The stress distribution for 0.5 mm restorative discs of each group was analyzed by Finite Element Analysis (FEA). The results of facture resistances were analyzed by one-way ANOVA and regression.
  
  
  RESULTS
  For the same thickness of testing discs, the fracture resistance of Group L was always significantly lower than the other two groups. The 0.5 mm discs in Group L resulted in the lowest value of 1028 (112) N. There was no significant difference between Group LS and Group ES when the restoration thickness ranged between 1.0 mm and 2.0 mm. There was a linear relation between fracture resistance and restoration thickness in Group L (R=0.621, P<0.001) and in Group ES (R=0.854, P<0.001). FEA showed a compressive permanent damage in all groups.
  
  
  CONCLUSIONS
  The materials tested in this in vitro study with the thickness above 0.5 mm could afford the normal bite force. When Lava Ultimate CAD/CAM is used, sandblasting is suggested to get a better bonding.
authors.affiliation: State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China; Department of Dental Materials Science, ACTA, University of Amsterdam and VU University Amsterdam, The Netherlands. Electronic address: isisschen@gmail.com.
authors.forename: Chenfeng
authors.initials: C
authors.lastname: Chen
authors.affiliation: Department of Dental Materials and Prosthodontics, São Paulo State University, São José dos Campos, São Paulo, Brazil.
authors.forename: Flávia Zardo
authors.initials: FZ
authors.lastname: Trindade
authors.affiliation: Department of Dental Materials Science, ACTA, University of Amsterdam and VU University Amsterdam, The Netherlands.
authors.forename: Niek
authors.initials: N
authors.lastname: de Jager
authors.affiliation: Department of Dental Materials Science, ACTA, University of Amsterdam and VU University Amsterdam, The Netherlands.
authors.forename: Cornelis J
authors.initials: CJ
authors.lastname: Kleverlaan
authors.affiliation: Department of Dental Materials Science, ACTA, University of Amsterdam and VU University Amsterdam, The Netherlands.
authors.forename: Albert J
authors.initials: AJ
authors.lastname: Feilzer
mesh_terms: D002516:Ceramics; D003188:Composite Resins; D020342:Finite Element Analysis; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D049329:Nanostructures
chemical_list: D003188:Composite Resins
keywords: CAD/CAM; Dental ceramic; Fracture resistance; Resin Nano Ceramic; Restoration thickness