Alterations of surface hardness with gypsum die hardeners

  • Harris P
  • Hoyer S
  • Lindquist T
 et al. 
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Statement of problem Die stones require abrasion resistance, dimensional stability with time, and high surface wettability material properties. Purpose The purpose of this study was to compare the surface microhardness (Knoop) of 4 contemporary gypsum materials with and without surface die hardener. Material and methods Materials used were a Type III stone (Microstone) and 3 die stones (Die-Keen, Silky-Rock, and ResinRock). Die hardener was cyanoacrylate (Permabond 910) or Clear Coat. Specimens of stone were hand mixed with distilled room temperature water and vacuum spatulated according to manufacturer's directions. Five cylinders (15 × 15 mm) per group were poured, using vibration, into phenolic ring molds positioned on top of a glass slide. The face of each specimen was polished with 2400-grit Al2O sandpaper. One face of each of 5 specimens/material was coated with cyanoacrylate; 5 specimens/material were coated with Clear Coat, air thinned and dried; and 5 specimens/material had no treatment (control). Knoop hardness (kg/mm2) readings were made on each face (5 readings/time point) 3, 12, and 24 hours after pouring. An ANOVA procedure with post hoc Tukey tests were performed (α=.05). Results Microhardness did not vary between 3 and 24 hours for any material (P>.05). Microstone had significantly lower surface hardness (P

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  • Paul E. Harris

  • Scott Hoyer

  • Terry J. Lindquist

  • Clark M. Stanford

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