title: Flexural strength and the probability of failure of cold isostatic pressed zirconia core ceramics.
abstract: BACKGROUND
  The flexural strength of zirconia core ceramics must predictably withstand the high stresses developed during oral function. The in-depth interpretation of strength parameters and the probability of failure during clinical performance could assist the clinician in selecting the optimum materials while planning treatment.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the flexural strength based on survival probability and Weibull statistical analysis of 2 zirconia cores for ceramic restorations.
  
  
  METHODS
  Twenty bar-shaped specimens were milled from 2 core ceramics, IPS e.max ZirCAD and Wieland ZENO Zr, and were loaded until fracture according to ISO 6872 (3-point bending test). An independent samples t test was used to assess significant differences of fracture strength (α=.05). Weibull statistical analysis of the flexural strength data provided 2 parameter estimates: Weibull modulus (m) and characteristic strength (σ(0)). The fractured surfaces of the specimens were evaluated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The investigation of the crystallographic state of the materials was performed with x-ray diffraction analysis (XRD) and Fourier transform infrared (FTIR) spectroscopy.
  
  
  RESULTS
  Higher mean flexural strength (P<.001) and σ(0) were recorded for WZ ceramics. However IZ ceramics presented a higher m value and a microstructure with fewer voids and pores. The fractured surfaces presented similar fractographic properties (mirror regions followed by hackle lines zones). Both groups primarily sustained the tetragonal phase of zirconia and a negligible amount of the monoclinic phase.
  
  
  CONCLUSIONS
  Although both zirconia ceramics presented similar fractographic and crystallographic properties, the higher flexural strength of WZ ceramics was associated with a lower m and more voids in their microstructure. These findings suggest a greater scattering of strength values and a flaw distribution that are expected to increase failure probability.
authors.affiliation: Department of Fixed Prosthesis and Implants Prosthodontics, Aristotle University of Thessaloniki, Thessaloniki, Greece.
authors.forename: Eleni
authors.initials: E
authors.lastname: Siarampi
authors.forename: Eleana
authors.initials: E
authors.lastname: Kontonasaki
authors.forename: Lambrini
authors.initials: L
authors.lastname: Papadopoulou
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Kantiranis
authors.forename: Triantafillia
authors.initials: T
authors.lastname: Zorba
authors.forename: Konstantinos M
authors.initials: KM
authors.lastname: Paraskevopoulos
authors.forename: Petros
authors.initials: P
authors.lastname: Koidis
mesh_terms: D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D006801:Humans; D008422:Materials Testing; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D008669:Metallurgy; D018583:Pliability; D015040:Zirconium / Q000737:chemistry*
chemical_list: D016876:Metal Ceramic Alloys; D015040:Zirconium; C028541:zirconium oxide