title: Failure modes of Y-TZP crowns at different cusp inclines.
abstract: OBJECTIVE
  To compare the reliability of the disto-facial (DF) and mesio-lingual (ML) cusps of an anatomically correct zirconia (Y-TZP) crown system. The research hypotheses tested were: (1) fatigue reliability and failure mode are similar for the ML and DF cusps; (2) failure mode of one cusp does not affect the failure of the other.
  
  
  METHODS
  The average dimensions of a mandibular first molar crown were imported into CAD software; a tooth preparation was modelled by 1.5 mm marginal high reduction of proximal walls and occlusal surface by 2.0 mm. The CAD-based tooth preparation was milled and used as a die to fabricate crowns (n=14) with porcelain veneer on a 0.5 mm Y-TZP core. Crowns were cemented on composite reproductions of the tooth preparation. The crowns were step-stress mouth motion fatigued with sliding (0.7 mm) a tungsten-carbide indenter of 6.25 mm diameter down on the inclines of either the DF or ML cusps. Use level probability Weibull curve with use stress of 200 N and the reliability for completion of a mission of 50,000 cycles at 200 N load were calculated.
  
  
  RESULTS
  Reliability for a 200 N at 50,000 cycles mission was not different between tested cusps. SEM imaging showed large cohesive failures within the veneer for the ML and smaller for the DF. Fractures originated from the contact area regardless of the cusp loaded.
  
  
  CONCLUSIONS
  No significant difference on fatigue reliability was observed between the DF compared to the ML cusp. Fracture of one cusp did not affect the other.
authors.affiliation: Dept. of Prosthodontics, University of Sao Paulo, Bauru School of Dentistry, Rua Vivaldo Guimaraes 17-62, Bauru 17012120, Sao Paulo, Brazil. estevamab@gmail.com
authors.forename: Estevam A
authors.initials: EA
authors.lastname: Bonfante
authors.forename: Irena
authors.initials: I
authors.lastname: Sailer
authors.forename: Nelson R F A
authors.initials: NR
authors.lastname: Silva
authors.forename: Van P
authors.initials: VP
authors.lastname: Thompson
authors.forename: E
authors.initials: E
authors.lastname: Dianne Rekow
authors.forename: Paulo G
authors.initials: PG
authors.lastname: Coelho
mesh_terms: D002484:Cementation; D017076:Computer-Aided Design; D003442:Crowns; D003776:Dental Porcelain / Q000737:chemistry*; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis / Q000295:instrumentation; D003801:Dental Veneers; D006801:Humans; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D008963:Molar; D019279:Resin Cements / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013871:Thiones / Q000737:chemistry; D019246:Tooth Preparation / Q000379:methods; D017973:Tungsten Compounds / Q000737:chemistry; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: C521707:Alloy Primer; D008689:Methacrylates; C483701:Rely X Unicem; D019279:Resin Cements; D013871:Thiones; D017973:Tungsten Compounds; C499362:yttria stabilized tetragonal zirconia; C002802:tungsten carbide; D003776:Dental Porcelain; D015019:Yttrium; D015040:Zirconium