title: Fatigue life and failure modes of crowns systems with a modified framework design.
abstract: OBJECTIVE
  To evaluate the effect of framework design on the fatigue life and failure modes of metal ceramic (MC, Ni-Cr alloy core, VMK 95 porcelain veneer), glass-infiltrated alumina (ICA, In-Ceram Alumina/VM7), and veneered yttria-stabilized tetragonal zirconia polycrystals (Y-TZP, IPSe.max ZirCAD/IPS e.max,) crowns.
  
  
  METHODS
  Sixty composite resin tooth replicas of a prepared maxillary first molar were produced to receive crowns systems of a standard (MCs, ICAs, and Y-TZPs, n=10 each) or a modified framework design (MCm, ICAm, and Y-TZPm, n=10 each). Fatigue loading was delivered with a spherical steel indenter (3.18mm radius) on the center of the occlusal surface using r-ratio fatigue (30-300N) until completion of 10(6) cycles or failure. Fatigue was interrupted every 125,000 cycles for damage evaluation. Weibull distribution fits and contour plots were used for examining differences between groups. Failure mode was evaluated by light polarized and SEM microscopy.
  
  
  RESULTS
  Weibull analysis showed the highest fatigue life for MC crowns regardless of framework design. No significant difference (confidence bound overlaps) was observed between ICA and Y-TZP with or without framework design modification. Y-TZPm crowns presented fatigue life in the range of MC crowns. No porcelain veneer fracture was observed in the MC groups, whereas ICAs presented bulk fracture and ICAm failed mainly through the veneer. Y-TZP crowns failed through chipping within the veneer, without core fractures.
  
  
  CONCLUSIONS
  Framework design modification did not improve the fatigue life of the crown systems investigated. Y-TZPm crowns showed comparable fatigue life to MC groups. Failure mode varied according to crown system.
authors.affiliation: Department of Prosthodontics, Integrated Center for Research, Bauru School of Dentistry, University of São Paulo, Bauru, SP 17012-901, Brazil.
authors.forename: Fabio C
authors.initials: FC
authors.lastname: Lorenzoni
authors.forename: Leandro M
authors.initials: LM
authors.lastname: Martins
authors.forename: Nelson R F A
authors.initials: NR
authors.lastname: Silva
authors.forename: Paulo G
authors.initials: PG
authors.lastname: Coelho
authors.forename: Petra C
authors.initials: PC
authors.lastname: Guess
authors.forename: Estevam A
authors.initials: EA
authors.lastname: Bonfante
authors.forename: Van P
authors.initials: VP
authors.lastname: Thompson
authors.forename: Gerson
authors.initials: G
authors.lastname: Bonfante
mesh_terms: D000537:Aluminum Oxide; D017438:Bisphenol A-Glycidyl Methacrylate; D002858:Chromium Alloys; D017076:Computer-Aided Design; D003442:Crowns; D003776:Dental Porcelain; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003801:Dental Veneers; D008348:Manikins; D016876:Metal Ceramic Alloys; D011092:Polyethylene Glycols; D011109:Polymethacrylic Acids; D011897:Random Allocation; D019279:Resin Cements; D016019:Survival Analysis; D015019:Yttrium; D015040:Zirconium
chemical_list: D002858:Chromium Alloys; D016876:Metal Ceramic Alloys; D011109:Polymethacrylic Acids; C462240:RelyX ARC; D019279:Resin Cements; C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; D015019:Yttrium; D015040:Zirconium; D000537:Aluminum Oxide