title: Applying microwave technology to sintering dental zirconia.
abstract: BACKGROUND
  When sintering zirconia, conventional processing may not provide uniform heating and consumes more energy than an alternative method using microwave energy.
  
  
  OBJECTIVE
  The purpose of this study was to compare the surface quality, mechanical and physical properties, and dimensional stability obtained by sintering yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) in a conventional furnace versus a microwave furnace.
  
  
  METHODS
  Twenty bars of Y-TZP were prepared from Zircad blocks. Ten specimens were used for sintering in a conventional furnace. The remaining 10 specimens were sintered in a microwave furnace. The sintering temperature used for both techniques was 1500°C. The flexural strength of all specimens was measured with the 3-point bend test with a universal testing machine with a cross head speed of 1.0 mm/min. Density was measured by applying the Archimedes method, and specimen length, width, and thickness were measured with a digital micrometer. The phase composition and average grain size of these ceramics were examined by using X-ray diffraction, and microstructure characteristics were studied with scanning electron microscopy. Data obtained were analyzed by using independent t tests (α=.05).
  
  
  RESULTS
  No significant difference between conventional and microwave sintering for either flexural strength, t18=0.49 (P=.63) or density, t18=0.07 (P=.95) was found. Specimens in both groups exhibited a uniform firing shrinkage of approximately 24.6% in all dimensions. The surface of selected specimens examined with a scanning electron microscope showed no visible difference in grain shape or porosity size between the 2 sintering methods.
  
  
  CONCLUSIONS
  Under the conditions of this study, it appears that either microwave or conventional zirconia sintering may be used for processing zirconia for dental use. However, microwave energy provides uniformity of heating, allowing the use of higher heating rates, which can increase productivity and save energy.
authors.affiliation: Al-Amiri Dental Center, Kuwait City, Kuwait.
authors.forename: Abdulredha A
authors.initials: AA
authors.lastname: Almazdi
authors.forename: Hasan M
authors.initials: HM
authors.lastname: Khajah
authors.forename: Edward A
authors.initials: EA
authors.lastname: Monaco
authors.forename: Hyeongil
authors.initials: H
authors.lastname: Kim
mesh_terms: D055598:Chemical Phenomena; D003776:Dental Porcelain / Q000737:chemistry; D017267:Dental Prosthesis Design / Q000379:methods*; D003799:Dental Stress Analysis; D004526:Efficiency; D006358:Hot Temperature; D008422:Materials Testing; D008872:Microwaves; D044367:Phase Transition; D018583:Pliability; D013499:Surface Properties; D013674:Technology, Dental / Q000379:methods*; D015019:Yttrium; D015040:Zirconium
chemical_list: C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; D015019:Yttrium; D015040:Zirconium