title: Linear dimensional change, compressive strength and detail reproduction in type IV dental stone dried at room temperature and in a microwave oven.
abstract: The type IV dental stone is widely used for the fabrication of dyes and master casts for fixed and removable partial prostheses. It is typically normal to wait at least 24 hours for the casts to dry prior to beginning the laboratory procedures. The waiting time has been shown to be greatly reduced by using microwave drying.
  
  
  OBJECTIVE
  This study evaluated the influence of drying techniques at room temperature and microwave oven on the linear dimensional change, compressive strength and detail reproduction in type IV dental stones.
  
  
  METHODS
  Three type IV dental stone brands were selected; elite Rock, Shera Premium and Durone IV. Two different drying protocols were tested in 4 groups (n=10); G-room temperature (25±4 ºC) dried for 2 hours; G2--room temperature dried for 24 hours; G3-room temperature dried for 7 days and G4--microwave oven dried at 800 W for 5 minutes and after 2 hours at room temperature. After drying, the samples were assayed for dimensional charges. The sample surface was submitted to the ImageTool 3.0 software for compressive strength in a universal testing machine with a cell load of 50 KN at a crosshead speed of 0.5 mm/minutes and the detail reproduction was analyzed with a stereomicroscope at 25x magnification. The statistical analysis of the linear dimensional change and compressive strength data were conducted by the ANOVA test followed by the Tukey test (p<0.05). Detailed reproduction values were reported in percentages.
  
  
  RESULTS
  For the compressive strength test, Elite Rock and Durone IV did not present significant differences between G2 and G4, while Shera Premium did not present differences between G3 and G4. The best reproduction levels were observed for G3.
  
  
  CONCLUSIONS
  Dental stone microwave oven drying showed a linear dimensional change similar to after room temperature drying for 24 hours and 7 days. The compressive strength of the stone dried in the microwave oven was similar to those dried at room temperature for 24 hours, with the exception of Shera Premium, which had similar results for microwave and room temperature drying for 7 days. For the microwave drying method the detail reproduction levels for samples dried at room temperature for 24 hours and 7 days were similar, except for the Durone IV.
authors.affiliation: Department of Restorative Dentistry, Dental Materials Division, Piracicaba Dental School, State University of Campinas, Piracicaba, SP, Brazil. marcos.bomfim@fop.unicamp.br
authors.forename: Marcos Aurélio Bomfim da
authors.initials: MA
authors.lastname: Silva
authors.forename: Rafael Pino
authors.initials: RP
authors.lastname: Vitti
authors.forename: Simonides
authors.initials: S
authors.lastname: Consani
authors.forename: Mário Alexandre Coelho
authors.initials: MA
authors.lastname: Sinhoreti
authors.forename: Marcelo Ferraz
authors.initials: MF
authors.lastname: Mesquita
authors.forename: Rafael Leonardo Xediek
authors.initials: RL
authors.lastname: Consani
mesh_terms: D000704:Analysis of Variance; D019245:Compressive Strength; D003735:Dental Casting Technique; D003764:Dental Materials / Q000737:chemistry / Q000528:radiation effects*; D006244:Hardness; D006801:Humans; D008422:Materials Testing; D008872:Microwaves; D003765:Models, Dental; D015203:Reproducibility of Results; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors
chemical_list: D003764:Dental Materials