title: Effects of artificial aging conditions on yttria-stabilized zirconia implant abutments.
abstract: BACKGROUND
  Most ceramic abutments are fabricated from yttria-stabilized tetragonal zirconia (Y-TZP). However, Y-TZP undergoes hydrothermal degradation, a process that is not well understood.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to assess the effects of artificial aging conditions on the fracture load, phase stability, and surface microstructure of a Y-TZP abutment.
  
  
  METHODS
  Thirty-two prefabricated Y-TZP abutments were screwed and tightened down to external hexagon implants and divided into 4 groups (n = 8): C, control; MC, mechanical cycling (1×10(6) cycles; 10 Hz); AUT, autoclaving (134°C; 5 hours; 0.2 MPa); and TC, thermal cycling (10(4) cycles; 5°/55°C). A single-load-to-fracture test was performed at a crosshead speed of 0.5 mm/min to assess the assembly's resistance to fracture (ISO Norm 14801). X-ray diffraction (XRD) analysis was applied to observe and quantify the tetragonal-monoclinic (t-m) phase transformation. Representative abutments were examined with high-resolution scanning electron microscopy (SEM) to observe the surface characteristics of the abutments. Load-to-fracture test results (N) were compared by ANOVA and Tukey test (α=.05).
  
  
  RESULTS
  XRD measurements revealed the monoclinic phase in some abutments after each aging condition. All the aging conditions reduced the fracture load significantly (P<.001). Mechanical cycling reduced the fracture load more than autoclaving (P=.034). No differences were found in the process of surface degradation among the groups; however, the SEM detected grinding-induced surface flaws and microcracks.
  
  
  CONCLUSIONS
  The resistance to fracture and the phase stability of Y-TZP implant abutments were susceptible to hydrothermal and mechanical conditions. The surface microstructure of Y-TZP abutments did not change after aging conditions.
authors.affiliation: Professor, Division of Prosthetic Dentistry, Metropolitan Union of Education and Culture, School of Dentistry, Bahia, Brazil. Electronic address: mariana_basilio@yahoo.com.br.
authors.forename: Mariana de Almeida
authors.initials: Mde A
authors.lastname: Basílio
authors.affiliation: Doctoral student, Department of Dental Materials and Prosthodontics, São Paulo State University (UNESP), Araraquara School of Dentistry, São Paulo, Brazil.
authors.forename: Kátia Vieira
authors.initials: KV
authors.lastname: Cardoso
authors.affiliation: Postdoctoral Researcher, Department of Physical Chemistry, São Paulo State University, Chemical Institute, São Paulo, Brazil.
authors.forename: Selma Gutierrez
authors.initials: SG
authors.lastname: Antonio
authors.affiliation: Associate Professor, Department of Medical Biophysics, Western University, Schulich School of Medicine & Dentistry, London, Ontario, Canada.
authors.forename: Amin Sami
authors.initials: AS
authors.lastname: Rizkalla
authors.affiliation: Chair, Restorative Dentistry, Department of Dentistry, Western University, Schulich School of Medicine & Dentistry, London, Ontario, Canada.
authors.forename: Gildo Coelho
authors.initials: GC
authors.lastname: Santos Junior
authors.affiliation: Adjunct Professor. Department of Dental Materials and Prosthodontics, São Paulo State University, Araraquara School of Dentistry, São Paulo, Brazil.
authors.forename: João Neudenir
authors.initials: JN
authors.lastname: Arioli Filho
mesh_terms: D000044:Dental Abutments; D003799:Dental Stress Analysis; D006801:Humans; D066298:In Vitro Techniques; D008855:Microscopy, Electron, Scanning; D013499:Surface Properties; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: D015019:Yttrium; D015040:Zirconium; C028541:zirconium oxide; C091417:yttria