title: Fatigue and damage accumulation of veneer porcelain pressed on Y-TZP.
abstract: OBJECTIVE
  This study compared the reliability and fracture patterns of zirconia cores veneered with pressable porcelain submitted to either axial or off-axis sliding contact fatigue.
  
  
  METHODS
  Forty-two Y-TZP plates (12mm x 12mm x 0.5mm) veneered with pressable porcelain (12mm x 12mm x 1.2mm) and adhesively luted to water aged composite resin blocks (12mm x 12mm x 4mm) were stored in water at least 7 days prior to testing. Profiles for step-stress fatigue (ratio 3:2:1) were determined from single load to fracture tests (n=3). Fatigue loading was delivered on specimen either on axial (n=18) or off-axis 30 degrees angulation (n=18) to simulate posterior tooth cusp inclination creating a 0.7mm slide. Single load and fatigue tests utilized a 6.25mm diameter WC indenter. Specimens were inspected by means of polarized-light microscope and SEM. Use level probability Weibull curves were plotted with 2-sided 90% confidence bounds (CB) and reliability for missions of 50,000 cycles at 200N (90% CB) were calculated.
  
  
  RESULTS
  The calculated Weibull Beta was 3.34 and 2.47 for axial and off-axis groups, respectively, indicating that fatigue accelerated failure in both loading modes. The reliability data for a mission of 50,000 cycles at 200N load with 90% CB indicates no difference between loading groups. Deep penetrating cone cracks reaching the core-veneer interface were observed in both groups. Partial cones due to the sliding component were observed along with the cone cracking for the off-axis group. No Y-TZP core fractures were observed.
  
  
  CONCLUSIONS
  Reliability was not significantly different between axial and off-axis mouth-motion fatigued pressed over Y-TZP cores, but incorporation of sliding resulted in more aggressive damage on the veneer.
authors.affiliation: Department of Prosthodontics, Integrated Center for Research, Bauru School of Dentistry, University of Sao Paulo, Bauru, Brazil. estevamab@gmail.com
authors.forename: Estevam A
authors.initials: EA
authors.lastname: Bonfante
authors.forename: Paulo G
authors.initials: PG
authors.lastname: Coelho
authors.forename: Petra C
authors.initials: PC
authors.lastname: Guess
authors.forename: Van P
authors.initials: VP
authors.lastname: Thompson
authors.forename: Nelson R F A
authors.initials: NR
authors.lastname: Silva
mesh_terms: D003188:Composite Resins / Q000737:chemistry; D003738:Dental Cements / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D003801:Dental Veneers; D006801:Humans; D021621:Imaging, Three-Dimensional; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D008859:Microscopy, Polarization; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D014867:Water / Q000737:chemistry; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry
chemical_list: D003188:Composite Resins; D003738:Dental Cements; D003764:Dental Materials; C499362:yttria stabilized tetragonal zirconia; D014867:Water; D003776:Dental Porcelain; D015019:Yttrium; D015040:Zirconium