title: Fracture toughness of yttria-stabilized zirconia sintered in conventional and microwave ovens.
abstract: BACKGROUND
  The fabrication of zirconium dioxide (ZrO2) dental prosthetic substructures requires an extended sintering process (8 to 10 hours) in a conventional oven. Microwave sintering is a shorter process (2 hours) than conventional sintering.
  
  
  OBJECTIVE
  The purpose of this study was to compare the fracture toughness of 3 mol % Y2O3-stabilized ZrO2 sintered in a conventional or microwave oven.
  
  
  METHODS
  Partially sintered ZrO2 specimens from 3 manufacturers, KaVo, Lava 3M, and Crystal HS were milled (KaVo Everest engine) and randomly divided into 2 groups: conventional sintering and microwave sintering (n=16 per group). The specimens were sintered according to the manufacturers' recommendations and stored in artificial saliva for 10 days. Fracture toughness was determined by using a 4-point bend test, and load to fracture was recorded. Mean fracture toughness for each material was calculated. A 2-way ANOVA followed by the Tukey HDS post hoc test was used to assess the significance of sintering and material effects on fracture toughness, including an interaction between the 2 factors (α=.05).
  
  
  RESULTS
  The 2-way ANOVA suggested a significant main effect for ZrO2 manufacturer (P<.001). The post hoc Tukey HSD test indicated that mean fracture toughness for the KaVo ZrO2 (5.85 MPa·m(1/2) ±1.29) was significantly higher than for Lava 3M (5.19 MPa·m(1/2) ±0.47) and Crystal HS (4.94 MPa·m(1/2) ±0.66) (P<.05) and no significant difference was observed between Lava 3M and Crystal HS (P>.05). The main effect of the sintering process (Conventional [5.30 MPa·m(1/2) ±1.00] or Microwave [5.36 MPa·m(1/2) ±0.92]) was not significant (P=.76), and there was no interaction between sintering and ZrO2 manufacturer (P=.91).
  
  
  CONCLUSIONS
  Based on the results of this study, no statistically significant difference was observed in the fracture toughness of ZrO2 sintered in microwave or conventional ovens.
authors.affiliation: Department of Restorative Dentistry, College of Dentistry, University of Illinois, Chicago, IL, USA. aristotelismarinis@yahoo.com
authors.forename: Aristotelis
authors.initials: A
authors.lastname: Marinis
authors.forename: Steven A
authors.initials: SA
authors.lastname: Aquilino
authors.forename: Peter S
authors.initials: PS
authors.lastname: Lund
authors.forename: David G
authors.initials: DG
authors.lastname: Gratton
authors.forename: Clark M
authors.initials: CM
authors.lastname: Stanford
authors.forename: Ana M
authors.initials: AM
authors.lastname: Diaz-Arnold
authors.forename: Fang
authors.initials: F
authors.lastname: Qian
mesh_terms: D002516:Ceramics / Q000737:chemistry*; D055598:Chemical Phenomena; D003461:Crystallography; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D005240:Feasibility Studies; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D008872:Microwaves; D018583:Pliability; D012464:Saliva, Artificial / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D015019:Yttrium / Q000737:chemistry* / Q000528:radiation effects; D015040:Zirconium / Q000737:chemistry* / Q000528:radiation effects
chemical_list: D003764:Dental Materials; D012464:Saliva, Artificial; C499362:yttria stabilized tetragonal zirconia; D015019:Yttrium; D015040:Zirconium; C028541:zirconium oxide