title: Fracture strength and fatigue resistance of all-ceramic molar crowns manufactured with CAD/CAM technology.
abstract: OBJECTIVE
  All-ceramic crowns are subject to fracture during function, especially in the posterior area. The use of yttrium-stabilized zirconium-oxide ceramic as a substructure for all-ceramic crowns to improve fracture resistance is unproven. The aim of this study was to compare fracture strength and fatigue resistance of new zirconium-oxide and feldspathic all-ceramic crowns made with computer-aided design/computer-aided manufacturing (CAD/CAM).
  
  
  METHODS
  An ivorine molar was prepared to receive an all-ceramic crown. Using epoxy resin, 40 replication dies were made of the prepared tooth. Twenty feldspathic all-ceramic crowns (Vita Mark II) (VMII) and 20 zirconium-oxide crown copings (In-Ceram YZ) (YZ) were made using CAD/CAM technique (CEREC-3D). The YZ copings were sintered and veneered manually with a fine-particle ceramic (VM9). All crowns were cemented to their respective dies using resin cement (Panavia F 2.0). Ten crowns in each group were subjected to compressive fatigue loading in a universal testing machine (instron). The other ten crowns from each group were loaded to fracture at a crosshead speed of 1 mm/min. Data were statistically analyzed using independent t-test and Fisher's exact test at alpha= 0.05.
  
  
  RESULTS
  There was a significant difference between the survival rates of the two materials during the fatigue test (p < 0.001). All VMII crowns survived without any crack formation, while all YZ crowns fractured (40%) or developed cracks (60%). All the YZ crown fractures occurred within the veneering layer during the fatigue test. There was no significant difference in mean fracture load between the two materials (p= 0.268). Mean fracture loads (standard deviation) in N were: 1459 (492) for YZ crowns and 1272 (109) for VMII crowns.
  
  
  CONCLUSIONS
  The performance of VMII crowns was superior to YZ crowns in the fatigue test. The premature fractures and cracks of the YZ crowns were attributed to weakness in the YZ veneer layer or in the core/veneer bond.
authors: Department of Prosthodontics, Faculty of Dentistry, University of Toronto, Toronto, ON, Canada.
authors: Mohammed
authors: M
authors: Zahran
authors: Omar
authors: O
authors: El-Mowafy
authors: Laura
authors: L
authors: Tam
authors: Philip A
authors: PA
authors: Watson
authors: Yoav
authors: Y
authors: Finer
mesh_terms: D000538:Aluminum Silicates; D002484:Cementation; D016009:Chi-Square Distribution; D019245:Compressive Strength; D017076:Computer-Aided Design; D003442:Crowns; D003776:Dental Porcelain; D017267:Dental Prosthesis Design; D003799:Dental Stress Analysis; D003801:Dental Veneers; D004548:Elasticity; D008422:Materials Testing; D008963:Molar; D018583:Pliability; D017680:Potassium Compounds; D011897:Random Allocation; D019279:Resin Cements; D015019:Yttrium; D015040:Zirconium
chemical_list: D000538:Aluminum Silicates; C438843:Panavia-Fluoro; D017680:Potassium Compounds; D019279:Resin Cements; C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; C016447:feldspar; D015019:Yttrium; D015040:Zirconium