This study investigated the expansion behavior of the rapid burnout and conventional types gypsum-bonded investments. Composition, setting expansion and thermal expansion of gypsum-bonded investment of 32 products were examined. The content of the refractory material ranged from 49.3〜78.5wt%: silica was the main component except in one product mainly containing alumina. The calcium sulfate hemihydrate concentration estimated to range from 19.9〜43.0wt%. The setting expansion at 120 minutes was 0.19〜2.29%, and the rapid burnout type investments tended to expand earlier and greater than the conventional ones. The rapid burnout type of investment showed a three-step expansion below 100℃, around 300 and at 550℃; and these expansions were respectively defined setting expansion, transformation of cristobalite and that of quartz.

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In this paper, the influence of the numbers of molds and the position in an electric furnace on the relationship between heating time and mold temperature was investigated using gypsum-bonded investment for quick heating, and the appropriate usage of the investment was studied. As a result, when a single mold was heated, the rate of increase in the temperature of the mold was lowest at the right front of a left hinge furnace. When five molds were heated at the same time, the rate was lower than that when a single mold was heated. The rate of the mold positioned at the center of furnace, which was surrounded by the four other molds, was the lowest. Molds should be repositioned in a furnace during heating to ensure uniform heating, or the order of casting should be determined in accordance with the mold temperature, when heating multiple molds at the same time.

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Basic properties of thermoplastic resins for denture base polymer (nylon resin: VLP, polycarbonate resin: PCB, acetal resin: ACT, polyethylene terephthalate resin: EST), which is referred to "non clasp denture," were examined to compare with those of heat-cured acrylic resin (PMMA). The flexural strengths and moduli of PCB and EST, and the properties of VLP and ACT were two-thirds and one-third of those of PMMA, respectively. The abrasion losses of thermoplastic resins were less than one-fifth of that of PMMA. The shear bond strengths of a chemical cured acrylic resin to PCB and EST were 1.5 times greater than that of PMMA, but those of VLP and ACT were very small. The color differences before and after coffee immersion of all specimens were less than 5, while those between before and after curry solution of VLP and EST were greater than 10. The water sorptions of VLP and EST were greater than those of the other products and one-third of that of PMMA. The water solubilities of thermoplastic resins were smaller than that of PMMA.

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