title: Effect of in vitro aging on the flexural strength and probability to fracture of Y-TZP zirconia ceramics for all-ceramic restorations.
abstract: OBJECTIVE
  Dental zirconia restorations should present long-term clinical survival and be in service within the oral environment for many years. However, low temperature degradation could affect their mechanical properties and survival. The aim of this study was to investigate the effect of in vitro aging on the flexural strength of yttrium-stabilized (Y-TZP) zirconia ceramics for ceramic restorations.
  
  
  METHODS
  One hundred twenty bar-shaped specimens were prepared from two ceramics (ZENO Zr (WI) and IPS e.max(®) ZirCAD (IV)), and loaded until fracture according to ISO 6872. The specimens from each ceramic (nx=60) were divided in three groups (control, aged for 5h, aged for 10h). One-way ANOVA was used to assess statistically significant differences among flexural strength values (P<0.05). The variability of the flexural strength values was analyzed using the two-parameter Weibull distribution function, which was applied for the estimation of Weibull modulus (m) and characteristic strength (σ0). The crystalline phase polymorphs of the materials (tetragonal, t, and monoclinic, m, zirconia) were investigated by X-ray diffraction (XRD) analysis, Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy.
  
  
  RESULTS
  A slight increase of the flexural strength after 5h, and a decrease after 10h of aging, was recorded for both ceramics, however statistically significant was for the WI group (P<0.05). Both ceramics presented a t→m phase transformation, with the m-phase increasing from 4 to 5% at 5h to around 15% after 10h.
  
  
  CONCLUSIONS
  The significant reduction of the flexural strength after 10h of in vitro aging, suggests high fracture probability for one of the zirconia ceramics tested.
authors.affiliation: Department of Fixed Prosthesis and Implants Prosthodontics, School of Dentistry, Aristotle University of Thessaloniki, GR 54124, Thessaloniki, Greece.
authors.forename: Eleni
authors.initials: E
authors.lastname: Siarampi
authors.affiliation: Department of Fixed Prosthesis and Implants Prosthodontics, School of Dentistry, Aristotle University of Thessaloniki, GR 54124, Thessaloniki, Greece.
authors.forename: Eleana
authors.initials: E
authors.lastname: Kontonasaki
authors.affiliation: Foundation for Research and Technology Hellas - Institute of Chemical Engineering Sciences (FORTH-ICE/HT), P.O. Box 1414, GR 26504, Rio - Patras, Greece.
authors.forename: Konstantinos S
authors.initials: KS
authors.lastname: Andrikopoulos
authors.affiliation: Department of Geology, Aristotle University of Thessaloniki, GR 54124, Thessaloniki, Greece.
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Kantiranis
authors.affiliation: Foundation for Research and Technology Hellas - Institute of Chemical Engineering Sciences (FORTH-ICE/HT), P.O. Box 1414, GR 26504, Rio - Patras, Greece.
authors.forename: George A
authors.initials: GA
authors.lastname: Voyiatzis
authors.affiliation: Physics Department, Aristotle University of Thessaloniki, GR 54124, Thessaloniki, Greece.
authors.forename: Triantafillia
authors.initials: T
authors.lastname: Zorba
authors.affiliation: Physics Department, Aristotle University of Thessaloniki, GR 54124, Thessaloniki, Greece.
authors.forename: Konstantinos M
authors.initials: KM
authors.lastname: Paraskevopoulos
authors.affiliation: Department of Fixed Prosthesis and Implants Prosthodontics, School of Dentistry, Aristotle University of Thessaloniki, GR 54124, Thessaloniki, Greece. Electronic address: pkoidis@dent.auth.gr.
authors.forename: Petros
authors.initials: P
authors.lastname: Koidis
mesh_terms: D000465:Algorithms; D002516:Ceramics / Q000737:chemistry*; D003461:Crystallography; D003764:Dental Materials / Q000737:chemistry*; D055119:Elastic Modulus; D008422:Materials Testing; D018583:Pliability; D011336:Probability; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D014961:X-Ray Diffraction; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003764:Dental Materials; C499362:yttria stabilized tetragonal zirconia; D015019:Yttrium; D015040:Zirconium
keywords: FTIR; Flexural strength; In vitro aging; Phase transformation; RAMAN; Weibull analysis; XRD; Zirconia ceramics