The purpose of this investigation was to study the setting time, fineness, setting expansion, compressive strength, consistency, detail reproduction, water-powder ratio, acidity, setting temperature rise and determination of free water of three
commercial dental model plasters (P - 1, P - 2 and P - 3), ten dental stones (S-1, S-2, S-3, S-4, S-5, S-6, S-7, S-8, S-9 and S-10), and three improved dental stones (IS-1, IS-2 and IS-3) used in Korea.
The following properties were studied: setting time, fineness, setting expansion, compressive strength, consistency, detail reproduction, water powder ratio, acidity, setting temperature rise and free water content. These tests were performed
according
to the KDA Specification No. 14: Dental plaster, stone and improved stone, KSP 5202: Dental plaster, RANSI/ADA Specification No. 25: Dental gypsum product, JIS T 6604: Dental plaster T 6605: Dental stone.
@ES From the experiments, the following results can be drawn:
@EN 1) The setting time of the dental gypsum products was 6.25 min. to 23.16 min, and the fineness of the dental gypsum products was as follows, the passed amount through No. 30 sieve was 99.73% to 100%, 62.25% to 98.31% through No. 100 sieve and
27.35%
to 84.92% through No. 200 sieve.
2) The setting expansion of the dental gypsum products was 0.047% to 0.278% after 2 hours. The compressive strength of the model plaster after 1 hour was 65.05±3.21 Kg/Cm2 to 85.42±7.02 Kg/Cm2, that of the stone was 223.68±24.47 Kg/Cm2 to
440.13±51.67 Kg/Cm2, and that of the improved stone was 320.53±27.94 Kg/Cm2 to 337.89±36.11 Kg/Cm2.
3) The consistency of the dental gypsum products was 24.1±1.27 mm to 36.2±2.64mm, the detail reproduction score was 2.5 to 4.0 and the water power ration was 59.98% to 65.15%.
4) The acidity of mixed supernatant water was pH 5.2 to pH 5.6, and the temperature rise during setting was 16.4℃ to 19.9℃ with the model plaster, that of the stone was 23.0℃ to 28.6℃ and that of the improved stone was 22.0℃ to 23.6℃.
5) The time to reach the peak temperature was 22.16 min. to 30.32 min with the model plaster, that of the stone was 13.63 min. to 59.66 min, and that of the improved stone was 36.10 min. to 69.13 min. The free water content was 0.1% and the
constitutional water content was 5.09% to .29% with the model plaster.
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