title: Use of plastic bar molded casting in the modification of variably expanding investment to compensate for casting shrinkage of nickel-chromium alloy.
abstract: Trial plastic bar molded castings were compared for accuracy with cast crowns by means of a nickel-chromium alloy, which was used to establish the liquid density of variably expanding investments. The plastic bars were invested to evaluate the change of expansion rate in a wide range of six liquid densities from 0% to 100%, and the distances between the sections were measured before and after casting. Wax crowns were cast to obtain a more detailed relation around 0% expansion at seven liquid densities, and the gaps between the base of the die and the margin of the crown were measured before and after casting. The expansion rates of both castings were calculated and thus were proportional to the liquid density; both regression curves indicated high correlation coefficients. As a result of the statistics of the Student's t-test, the difference between the two methods was not significant. The trial plastic bar was useful in establishing the variably expanding investment for precise casting of artificial crowns.
authors.affiliation: Department of Prosthetic Dentistry, Hiroshima University, School of Dentistry, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Shigeto
authors.forename: H
authors.initials: H
authors.lastname: Iwanaga
authors.forename: T
authors.initials: T
authors.lastname: Hamada
mesh_terms: D002858:Chromium Alloys / Q000737:chemistry*; D003442:Crowns; D003734:Dental Casting Investment; D003735:Dental Casting Technique / Q000295:instrumentation*; D010969:Plastics; D012044:Regression Analysis; D015203:Reproducibility of Results
chemical_list: D002858:Chromium Alloys; D003734:Dental Casting Investment; D010969:Plastics