title: Hydrothermal degradation of a 3Y-TZP translucent dental ceramic: A comparison of numerical predictions with experimental data after 2 years of aging.
abstract: OBJECTIVE
  The purpose of the study was to assess the hydrothermal resistance of a translucent zirconia with two clinical relevant surface textures by means of accelerated tests (LTD) and to compare predicted monoclinic fractions with experimental values measured after two years aging at 37°C.
  
  
  METHODS
  Polished (P) and ground (G) specimens were subjected to hydrothermal degradation by exposure to water steam at different temperatures and pressures. The t-m phase transformation was quantified by grazing incidence X-ray diffraction (GIXDR). The elastic modulus and hardness before- and after LTD were determined by nanoindentation.
  
  
  RESULTS
  G specimens presented a better resistance to hydrothermal degradation than P samples. Activation energies of 89 and 98kJ/mol and b coefficients of 2.0×10(-5) and 1.8×10(-6) were calculated for P and G samples respectively. The coefficients were subsequently used to predict transformed monoclinic fractions at 37°C. A good correlation was found between the predicted values and the experimental data obtained after aging at 37°C during 2 years. Hydrothermal degradation led to a significant decrease of the elastic moduli and hardness in both groups.
  
  
  CONCLUSIONS
  The dependency of the t-m phase transformation rate on temperature must be determined to accurately predict the hydrothermal behavior of the zirconia ceramics at oral temperatures. The current prevailing assumption, that 5h aging at 134°C corresponds to 15-20 years at 37°C, will underestimate the transformed fraction of the translucent ceramic at 37°C. In this case, the mechanical surface treatment influences the ceramic's transformability. While mild grinding could potentially retard the hydrothermal transformation, polishing after occlusal adjustment is recommended to prevent wear of the antagonist teeth and maintain structural strength.
authors.affiliation: Division of Fixed Prosthodontics and Biomaterials, University Clinic of Dental Medicine, University of Geneva, Geneva, Switzerland. Electronic address: Maria.Cattani-Lorente@unige.ch.
authors.forename: Maria
authors.initials: M
authors.lastname: Cattani-Lorente
authors.affiliation: Division of Fixed Prosthodontics and Biomaterials, University Clinic of Dental Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Durual
authors.affiliation: HEPIA, University of Applied Sciences - Western Switzerland, Geneva, Switzerland.
authors.forename: Michel
authors.initials: M
authors.lastname: Amez-Droz
authors.affiliation: Division of Fixed Prosthodontics and Biomaterials, University Clinic of Dental Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: H W Anselm
authors.initials: HW
authors.lastname: Wiskott
authors.affiliation: Division of Fixed Prosthodontics and Biomaterials, University Clinic of Dental Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: Susanne S
authors.initials: SS
authors.lastname: Scherrer
mesh_terms: D002516:Ceramics / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D006244:Hardness; D006358:Hot Temperature; D008422:Materials Testing; D015233:Models, Statistical; D044367:Phase Transition; D013499:Surface Properties; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003764:Dental Materials; D015019:Yttrium; D015040:Zirconium; C028541:zirconium oxide
keywords: Activation energy; Elastic modulus; Hardness; Hydrothermal degradation (LTD); Translucent 3Y-TZP zirconia ceramic; t–m phase transformation