title: The influence of postpouring time on the roughness, compressive strength, and diametric tensile strength of dental stone.
abstract: BACKGROUND
  The optimum time after pouring a dental impression before removing the dental cast is unknown with regard to the strength and roughness of the stone. Setting times and the commercial products used are important variables.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the effect of postpouring time on the surface roughness, compressive strength, and diametric tensile strength of Type IV dental stone.
  
  
  METHODS
  A total of 270 specimens were prepared from 3 commercial brands of dental stone (Durone, Fuji Rock, and Tuff Rock). Surface roughness, compressive strength, and diametric tensile strength were assessed at 1 hour, 24 hours, and 7 days after pouring. Specimens 6 mm in diameter and 3 mm in height were produced for roughness and diametric tensile strength tests. Specimens 3 mm in diameter and 6 mm in height were used to measure compressive strength. The results were analyzed with the general linear model and Tukey honestly significant difference test (α=.05).
  
  
  RESULTS
  The surface roughness measured for the different types of dental stone tested varied from 0.3 μm (Durone, 1 hour) to 0.64 μm (Tuff Rock, 7 days). The diametric tensile strength ranged from 3.94 MPa (Tuff Rock, 1 hour) to 9.20 MPa (Durone, 7 days). The compressive strength varied from 26.67 MPa (Durone, 1 hour) to 65.14 MPa (Fuji Rock, 7 days).
  
  
  CONCLUSIONS
  Surface roughness (P=.005), diametric tensile strength (P=.001), and compressive strength (P=.001) increased significantly with time after pouring. The commercial brand used affected roughness (P=.001), diametric tensile strength (P=.004), and compressive strength (P=.001). Tuff Rock exhibited the highest surface roughness. The highest diametric tensile strength values were recorded for Durone and Fuji Rock. Fuji Rock exhibited the highest compressive strength.
authors.affiliation: Postgraduate student, Postgraduate Program in Dentistry, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Brazil.
authors.forename: Leonardo
authors.initials: L
authors.lastname: De Cesero
authors.affiliation: Associate Professor, Clinical Department, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Brazil. Electronic address: eduardo.mota@pucrs.br.
authors.forename: Eduardo Gonçalves
authors.initials: EG
authors.lastname: Mota
authors.affiliation: Associate Professor, Clinical Department, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Brazil.
authors.forename: Luiz Henrique
authors.initials: LH
authors.lastname: Burnett
authors.affiliation: Associate Professor, Clinical Department, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Brazil.
authors.forename: Ana Maria
authors.initials: AM
authors.lastname: Spohr
mesh_terms: D002133:Calcium Sulfate / Q000737:chemistry*; D019245:Compressive Strength; D003734:Dental Casting Investment / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D006801:Humans; D008422:Materials Testing; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013718:Tensile Strength; D013997:Time Factors
chemical_list: D003734:Dental Casting Investment; D002133:Calcium Sulfate