In a two-chamber pressure-casting system, the rate of casting pressure increase depends on the exhausting rate of argon gas in the mold. The purpose of this study was to measure the pressure change in a mold cavity after the start of casting and to investigate the influence of mold temperature and thickness on the initial rate and later value of casting pressure. Moreover, a new casting mold with an experimentally improved crucible was proposed and its influence on the casting pressure was also investigated. Regardless of crucible condition, the initial rate of casting pressure decreased with mold temperature and thickness. Although the difference in crucible condition did not significantly influence the initial rate, the improved crucible increased the later value of casting pressure.

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This study investigated the effect of storage of alginate impressions in sealed bags following spray with disinfectant solutions on the dimensional accuracy and deformation of stone models. For ten brands of alginate impression materials, the dimensional changes in 100% relative humidity for 2 hours were measured. Among them, Aroma Fine DFIIIand Alginoplast EM, which showed the greater and smaller contraction, respectively, and Alflex, showing expansion, were chosen as test materials. Impressions were spraved with 1% sodium hypochlorite solution (1SHS) or 2% glutaraldehyde solution (2GAS), and stored in sealed bags for 2 hours. Then, mixed stones were poured into the treated impressions. The results indicated the storage in a sealed bag for 2 hours after spraying with either 1SHS or 2GAS did not effect the dimensional accuracy and deformation of stone models, when an alginate impression characterized by smaller contraction in 100% relative humidity was chosen for use.

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Methylene blue, hematoporphyrin and tar were used in pigmentation models to investigate whether titanium dioxide photocatalyst could be used to remove plaque or tar on dentures. Titanium dioxide and small amounts of acids were used to prepare a titanium dioxide (Ti0_2) cleansing agent. The Ti0_2 cleansing agent discolored methylene blue from 10 ppm to 5 ppm or less over 2 minutes. It increased the L^* value of hematoporphyrin-stained test paper strips from about 60 to about 90 and decreased the a^* value from about 20 to 0 or less, discoloring the reddish brown color of hematoporphyrin. The cleansing agent also discolored tar, asΔL^*, the change in L^* by cleaning, was as high as 14.43, with Δa^* and Δb^* being as low as -8.35 and -8.15, respectively. This study indicated that Ti0_2 photocatalyst could clean dentures in a safe simple manner without damaging them.

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The purpose of this study was to examine the biocompatibility of a newly developed β type titanium alloy (Ti-13Ta-29Nb-4.6Zr). Ti-13Ta-29Nb-4.6Zr, Ti-6Al-4V, Ti, Ni and Cu were implanted in subcutaneous pouches in the backs of ddy mice, and sham operations were performed on controls. Proinflammatory cytokines (IL-1 α, β, IL-6 and IL-1 ra) were detected in the tissues around the alloy by immunohistochemical methods. The results were as follows : the levels of expression of every proinflammatory cytokine in mice with Ti-13Ta-29Nb-4.6Zr implants were lower than in the Cu and Ni groups. However, the level of IL-1 β exoression induced by the new alloy was higher than in the Ti and sham groups, and a higher level of IL-6 expression than sham in the group was detected at 10 days. We concluded that Ti-13Ta-29Nb-4.6Zr may have equivalent biocompatibility to the existing Ti alloy However, our findings is suggested that the differences in the elements included in the materials may affect the host response.

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FRP esthetic orthodontic wires were fabricated from CPSA glass fibers and Bis-GMA resin. The water absorption and change of mechanical properties were investigated in wet condition to simulate use in the oral cavity. As a result, the mechanical properties declined after water absorption for 3〜6 hours. Decline of load and micro fracturing were found to be correlated by acoustic emission measurement during the stress relaxation test. In wet condition, AEs was 5〜9 times higher than in dry condition. Silane-coupling suppressed the generation of micro fractures and decline of load. The modulus of longitudinal elasticity and load at 2 mm deflection in the flexural test was reduced by half and the permanent deflection increased after 24/hours under 2 mm fixed bending in wet condition. These changes were well represented using the energy required for 2 mm deflection as a single evaluation index. Silane-coupling agent decreased the exfoliation of glass fiber/matrix interface and suppressed the decline of mechanical properties.

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A shape analysis system using a CCD camera for recording specimen geometry at room temperature and heating was experimentally produced.A window for observation was added to the muffle furnace door. In an investment specimen with control points marked by pencil, it was possible to make observations on shape change from room temperature to 400℃ by automated analysis. The results of investment specimen measurement by this system showed good agreement with the results of extrapolated coefficients of thermal expansion obtained by thermomechanical analysis apparatus at a measuring load of 0.

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