A study of the surface-roughness and fit of crowns made with gypsum-bonded investment mixed with smectite solutions
Gypsum-boned investment was mixed with various concentrations of water-solube smectite with marked thixotropy, and the effects of smectite on the surface-roughness and fit of crowns were studied. In the experiment, two kinds of commencial gypsum-bonded investment were mixed with four different concentrations of smectite solutions at the standard water mixing ratio Specular resin patterns and model crown wax patterns were used, and the moulds were heated at four different temperatures.
Results: As the concentration of smectite increased, the fit of the cast crowns increased for cristobalite investment, but decreased for quartz investment. The fit of crowns increased for SWN but decreased for SWF, and the surface-roughness decreased for both. The surface-roughness was smaller for SWF than for SWN.
Key wordsSmectite Quartz investment Casting accuracy Surface roughness Cristobalite investment Thixotropy Casting crown
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