title: Composition, phase analysis, biaxial flexural strength, and fatigue of unshaded versus shaded Procera zirconia ceramic.
abstract: BACKGROUND
  Recent interest in shaded zirconia has raised questions about the relative stability of the tetragonal phase after colorant oxide additions.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to evaluate the effects of fatigue cycling on the stability of a commercially available dental zirconia (Procera) in both unshaded and shaded compositions by measuring the change in biaxial flexural strength (BFS) after 500 000 cycles at 80-N loads and in phase composition as detected by x-ray diffraction (XRD).
  
  
  METHODS
  Partially stabilized zirconia disks (NobelProcera) were fabricated in unshaded and shaded forms (12 mm diameter × 0.8 mm thick). Specimens were analyzed by energy-dispersive x-ray spectroscopy (EDS) and by wavelength-dispersive x-ray spectroscopy (WDS) for oxide compositions which indicated the presence of small amounts of Fe-O (0.13 ±0.10 wt %) in the shaded specimens. XRD focused on the tetragonal (T) and monoclinic (M) peaks in the 20 to 40 degrees 2θ range. The disks were polished on 1 side, cyclically loaded (80N, 500 000 cycles, custom 4-station fatigue test machine), and tested for residual BFS after cycling. Unshaded (U) and shaded groups (S) were compared before (U1, S1) and after (U2, S2) load cycling with XRD and residual BFS.
  
  
  RESULTS
  Residual BFS (MPa) for specimens before (U1=856 ±99 versus S1= 842 ±40) and after fatigue (U2=772 ±65 versus S2= 718 ±68) were statistically different (U1 versus U2; S1 versus S2; U2 versus S2, P<.05). The XRD of U1 and S1 specimens revealed tetragonal and cubic zirconia. U2 and S2 specimens contained tetragonal zirconia, with the initial appearance of small amounts of monoclinic zirconia after fatigue cycling. Monoclinic detection was measured on the tension side of the tested specimens and varied between tests at the center and radially at 4 mm.
  
  
  CONCLUSIONS
  The results indicated shaded materials more readily transform the tetragonal to the monoclinic phase during load cycling than unshaded ones. However, extrapolating the effects of any shortening of the service life of zirconia compositions is difficult. The potential mitigating effects of other factors such as the thermal postprocessing of porcelain veneers, stains on zirconia, or effects of water have yet to be investigated.
authors.affiliation: Clinical Assistant, Department of Prosthodontics and Doctural student, Department of Biomaterials, The National and Kapodistrian University of Athens, School of Dentistry, Athens, Greece. Electronic address: pespyr@gmail.com.
authors.forename: Panagiota-Eirini
authors.initials: PE
authors.lastname: Spyropoulou
authors.affiliation: Assistant Professor, Department of Prosthodontics, The National and Kapodistrian University of Athens, School of Dentistry, Athens, Greece.
authors.forename: Phophi
authors.initials: P
authors.lastname: Kamposiora
authors.affiliation: Professor, Department of Biomaterials, The National and Kapodistrian University of Athens, School of Dentistry, Athens, Greece.
authors.forename: George
authors.initials: G
authors.lastname: Eliades
authors.affiliation: Assistant Professor, Department of Prosthodontics, The National and Kapodistrian University of Athens, School of Dentistry, Athens, Greece.
authors.forename: George
authors.initials: G
authors.lastname: Papavasiliou
authors.affiliation: Professor, Department of Biologic and Materials Sciences, Division of Prosthodontics, The University of Michigan, School of Dentistry, Ann Arbor, Mich.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Razzoog
authors.affiliation: Professor, Department of Prosthodontics, College of Dental Medicine, Nova Southeastern University, Ft. Lauderdale, Fla.
authors.forename: Jeffrey Y
authors.initials: JY
authors.lastname: Thompson
authors.affiliation: Senior Product Reliability Engineer, Corning Inc, Corning, NY.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Smith
authors.affiliation: Professor and Chair, Department of Cariology, Restorative Sciences and Endodontics, University of Michigan, School of Dentistry, Ann Arbor, Mich.
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Bayne
mesh_terms: D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis; D006801:Humans; D008422:Materials Testing; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D017797:Prosthesis Coloring; D013052:Spectrometry, X-Ray Emission; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
chemical_list: D016876:Metal Ceramic Alloys; C077451:Procera; D003776:Dental Porcelain; D014025:Titanium