title: Tensile strength of type IV dental stones dried in a microwave oven.
abstract: BACKGROUND
  It is known that drying dental stones in a microwave oven can save time, but the strength of the material may be affected by different drying methods.
  
  
  OBJECTIVE
  This study evaluated the diametral tensile strength (DTS) of 5 type IV gypsum products at different time intervals using microwave and air-drying methods.
  
  
  METHODS
  . A total of 300 cylinder specimens were prepared from 5 type IV dental stones (Moldano, Amberok, Herastone, Shera-Sockel, and Fujirock; n = 60 per stone) in accordance with the manufacturers' recommendations. Half of the specimens of each stone (n = 30) were dried in open air within a temperature range of 20 +/- 2 degrees C; the other half (n = 30) underwent initial setting in a silicone rubber mold in open air for 10 minutes and then were dried in a microwave oven for 10 minutes. Within these groups, 10 specimens were tested under diametral compression at each of the following time periods: 30, 60, and 120 minutes after drying. Three-way analysis of variance and Scheffe's post hoc test were performed for statistical comparisons at a significance level of P<.05.
  
  
  RESULTS
  At all time intervals, the diametral tensile strength values for dental stones dried in a microwave oven (mean 2.99 MPa) were significantly higher (P<.01) than the values for specimens dried in open air (mean 2.53 MPa).
  
  
  CONCLUSIONS
  Within the limitations of this study, microwave oven drying had a positive effect on the diametral tensile strength of 5 type IV dental stones.
authors.affiliation: Faculty of Dentistry, University of Hacettepe, Ankara, Turkey. nhersek@hotmail.com
authors.forename: Nur
authors.initials: N
authors.lastname: Hersek
authors.forename: Senay
authors.initials: S
authors.lastname: Canay
authors.forename: Kivanç
authors.initials: K
authors.lastname: Akça
authors.forename: Yalçin
authors.initials: Y
authors.lastname: Ciftçi
mesh_terms: D000388:Air; D000704:Analysis of Variance; D002133:Calcium Sulfate; D003734:Dental Casting Investment; D003799:Dental Stress Analysis; D003890:Desiccation; D008422:Materials Testing; D008872:Microwaves; D018709:Statistics, Nonparametric; D013674:Technology, Dental / Q000295:instrumentation; D013718:Tensile Strength
chemical_list: D003734:Dental Casting Investment; D002133:Calcium Sulfate