title: Biaxial flexural strength, elastic moduli, and x-ray diffraction characterization of three pressable all-ceramic materials.
abstract: BACKGROUND
  Before the release of an advanced ceramic material, independent assessment of its strength, elastic modulus, and phase composition is necessary for comparison with peer materials.
  
  
  OBJECTIVE
  This study compared the biaxial flexural strength, elastic moduli, and crystalline phases of IPS Empress and Empress 2 with a new experimental ceramic.
  
  
  METHODS
  Twenty standardized disc specimens (14 x 1.1 mm) per material were used to measure the biaxial strength. With a universal testing machine, each specimen was supported on 3 balls and loaded with a piston at a crosshead speed of 0.5 mm/min until fracture. Three standardized bars (30 x 12.75 x 1.1 mm) for each material were prepared and excited with an impulse tool. The resonant frequencies (Hz) of the bars were used to calculate the elastic moduli with the equation suggested by the standard ASTM (C 1259-94). X-ray diffraction with Cu Kalpha at a diffraction angle from 20 to 40 degrees was used to identify the crystalline phases by means of a diffractometer attached to computer software. The data were analyzed with 1-way analysis of variance followed by pairwise t tests (P<.05).
  
  
  RESULTS
  Mean biaxial strengths were 175 +/- 32, 407 +/- 45, and 440 +/- 55 MPa for IPS Empress, Empress 2, and the experimental ceramic, respectively. Elastic modulus results were 65, 103, and 91 GPa for the same materials, respectively. There was no significant difference in strength and elastic modulus between Empress 2 and the experimental ceramic. Both materials demonstrated a significantly higher elastic modulus and strength than IPS Empress. X-ray diffraction revealed leucite as the main crystalline phase for IPS Empress and lithium disilicate for both Empress 2 and the experimental ceramic.
  
  
  CONCLUSIONS
  Within the limitations of this study, the improved mechanical properties of Empress 2 and experimental ceramic over those of IPS Empress were attributed to the nature and amount of their crystalline content lithium disilicate.
authors.affiliation: Biomaterials Research Unit, Faculty of Dentistry, University of Sydney, National Innovation Centre, Eveleigh, New South Wales, Australia. albakrym@hotmail.com
authors.forename: Mohammad
authors.initials: M
authors.lastname: Albakry
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Guazzato
authors.forename: Michael Vincent
authors.initials: MV
authors.lastname: Swain
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D000704:Analysis of Variance; D002516:Ceramics / Q000737:chemistry*; D003461:Crystallography; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D004548:Elasticity; D006801:Humans; D018020:Lithium Compounds / Q000737:chemistry; D016555:Matched-Pair Analysis; D008422:Materials Testing; D018583:Pliability; D013314:Stress, Mechanical; D013499:Surface Properties; D014961:X-Ray Diffraction
chemical_list: D000538:Aluminum Silicates; C118557:Empress 2; C075815:IPS-Empress ceramic; D018020:Lithium Compounds; D003776:Dental Porcelain