title: Effect of sintering time on biaxial strength of zirconium dioxide.
abstract: OBJECTIVE
  Aim of this study was to evaluate effect of sintering time on mechanical properties of yttrium partially stabilized zirconia (Y-TZP) (ICE Zirkon, ZirkonZahn, Italy).
  
  
  METHODS
  Fifty-six zirconia discs were divided into two groups. Discs of the first group were sintered in sintering oven (ZirkonZahn) at 20-1500 degrees C temperature using rise time of 3 h and kept at 1500 degrees C for 2 h. Discs of the second group were sintered at 20-1500 degrees C using rise time of 1h 40 min and kept at 1500 degrees C for 1 h. Half of the discs (n=15) from both groups were thermocycled in distilled water for 20000 cycles (5-55 degrees C). Biaxial flexural strength of the discs (diameter 19.0 mm, thickness 1.6 mm) were measured dry at room temperature. Surface microhardness (VHN) was also measured. X-Ray diffraction analysis was performed to evaluate the ratio of tetragonal to monoclinic phase in thermocycled discs. The data was calculated using Weibull and ANOVA analysis.
  
  
  RESULTS
  No statistically significant difference (p>0.05) was found between the groups in terms of sintering time or thermocycling. The biaxial flexural strength of the groups varied from 995MPa to 1127MPa. Surface microhardness varied from 1478 to 1532. The relative amount of the monoclinic phase was higher when zirconia was thermocycled and stored in water compared to control discs, which had no monoclinic phase at all.
  
  
  CONCLUSIONS
  Variation in the sintering time from 1.6h to 3.0 h did not influence mechanical properties of Y-TZP zirconia.
authors.affiliation: University of Turku, Department of Prosthetic Dentistry and Biomaterials Science, Turku, Finland. jenhje@utu.fi
authors.forename: Jenni
authors.initials: J
authors.lastname: Hjerppe
authors.forename: Pekka K
authors.initials: PK
authors.lastname: Vallittu
authors.forename: Kaj
authors.initials: K
authors.lastname: Fröberg
authors.forename: Lippo V J
authors.initials: LV
authors.lastname: Lassila
mesh_terms: D002516:Ceramics / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry*; D055119:Elastic Modulus; D006244:Hardness; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D010316:Particle Size; D044367:Phase Transition; D018583:Pliability; D013314:Stress, Mechanical; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry*
chemical_list: D003764:Dental Materials; C499362:yttria stabilized tetragonal zirconia; D014867:Water; D015019:Yttrium; D015040:Zirconium; C028541:zirconium oxide