title: Off-axis sliding contact reliability and failure modes of veneered alumina and zirconia.
abstract: OBJECTIVE
  All-ceramic dental crowns are popular because of their esthetics and biocompatibility. However, they often chip or fracture when subjected to repeated occlusal loading. Considerable efforts to improve the materials are being done through the study of fatigue and failure modes. The vast majority of fatigue studies have been conducted with uniaxial loading and no sliding action. We hypothesized different failure modes for porcelain veneered Y-TZP and that the reliability of porcelain veneered Y-TZP is higher than that of porcelain veneered alumina when subjected to fatigue under 30 degrees off-axis sliding Y-TZP and alumina plates were porcelain veneered and cemented to aged composite blocks as a model for an all-ceramic crown on dentin.
  
  
  METHODS
  Specimens (n=21 per group) were fatigue at 30 degrees off-axis with a hard sphere sliding contact in water, by means of a mouth-motion simulator apparatus.
  
  
  RESULTS
  Although no difference between groups was found, the failure modes differed and there was a tendency to higher reliability for Y-TZP compared to alumina for a mission of 50,000 cycles at 150N load.
  
  
  CONCLUSIONS
  Failure modes for alumina specimens were deep penetrating partial cone cracks and cementation internal surface radial cracks. Y-TZP specimens showed only surface damage with deep penetrating partial cone cracks extending to the veneer core interface, with no cementation surface radial cracking, which overall agrees with clinical finding. Angled sliding contact appears to better simulate oral function.
authors.affiliation: Department of Biomaterials and Biomimetics, New York University College of Dentistry, USA.
authors.forename: Tomasa
authors.initials: T
authors.lastname: Santana
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhang
authors.forename: Petra
authors.initials: P
authors.lastname: Guess
authors.forename: Van P
authors.initials: VP
authors.lastname: Thompson
authors.forename: Elizabeth Dianne
authors.initials: ED
authors.lastname: Rekow
authors.forename: Nelson R F A
authors.initials: NR
authors.lastname: Silva
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry*; D002484:Cementation; D003188:Composite Resins / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry*; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis / Q000295:instrumentation; D003801:Dental Veneers; D006801:Humans; D008422:Materials Testing; D008859:Microscopy, Polarization; D018583:Pliability; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D013499:Surface Properties; D017973:Tungsten Compounds / Q000737:chemistry; D014867:Water / Q000737:chemistry; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry*
chemical_list: C105314:AllCeram; D003188:Composite Resins; D003764:Dental Materials; D017973:Tungsten Compounds; C499362:yttria stabilized tetragonal zirconia; D014867:Water; C002802:tungsten carbide; D003776:Dental Porcelain; D015019:Yttrium; D015040:Zirconium; D000537:Aluminum Oxide; C028541:zirconium oxide