As part of a study about the disinfection of impressions in dental treatment of elderly patients at home, we investigated the effect of immersion disinfection of alginate impressions on the dimensional accuracy and deformation of edentulous working casts in relation to the type of tray for alginate impressions. Two types of alginate impression materials : AROMA FINE DFIII (AFIII) and Jeltrate Plus (JLP), characterized by smaller or greater dimensional changes in water, were used. Four types of experimental metal trays (perforated trays opened or closed mesio-distally, unperforated trays opened or closed mesio-distally) were prepared as impression trays. Impressions were immersed in 1% sodium hypochlorite solution for 10 min or 2% glutaraldehyde solution for 30 min. Whichever tray to use for AFIII impression, the dimensional accuracy and deformation of edentulous working casts was only slightly affected by immersion in 1% sodium hypochlorite solution for 10 min.

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The cushioning effects of casting ring liners on the setting expansion of the investment material in split metal molds with internal dimensions of 30 mm diameter and 40 mm height were evaluated based on the decrease in the thickness of dry ceramic liners and asbestos ribbons. Setting expansion of investment material was 0.35%, and requirement of decrease in thickness of liners was 0.05 mm. Decreases in the thickness of liners (δTs) were within -0.075 to 0.278 mm. δTs at bottom side were larger than those of upper side. δTs tended to increase with the original thickness of the liner. In liners with high water sorption, it was indicated that water absorbency and water retentiveness of the liner influenced the setting and hygroscopic expansion of the investment material. In liners with low water sorption, δTs tended to increase as the cushioning effect assessed by a setting expansion measuring apparatus increased.

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Our previous study showed that the values of surface roughness for direction-dependent grooves on the standard surface roughness plates were dependent on the measuring angle (MA). Thus, the parameter of surface roughness might differ appreciably for different MA values. This study was to evaluate the effects of directional dependence of surface roughness on standard surface roughness plates with direction-dependent grooves. The optimal MA for direction-dependent surface roughness was determined by equivalent equation of a wave length parameter (Rλa). The optimal angle range of MA was determined by the Rλa-tolerance (Rλa-TOL) method in terms of 10% TOL value of equivalent equation of Rλa. This Rλa-TOL method was effective for measuring direction-dependent surface roughness, such as that of the standard surface roughness plate.

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The correlation of between cytotoxicity testing using the neutral red method and a new method for toxicity test using changes in membrane fluidity in PL cells derived from human periodontal membrane was examined. The ranking order of cell toxicity when cells were treated with acrylic resin monomers for 3hrs was trimethylolpropane trimethacrylate (TMPT)≥epoxy methacrylate (D-GMA)>1,4-buthane diol dimethacrylate (BD)>1,3-buthylene glycol dimethacrylate (BG)>ethylene glycol dimethacrylate (1G)>triethylene glycol dimethacrylate (3G)>methyl methacrylate (MMA) and also that for 24 hrs was analogous to that of 3-hr treatment. Changes in fluorescence anisotropy of cells treated with various monomers increased in the order of D-GMA, 1G, TMPT, BG, BD, 3G, MMA. A good correlation was found between these two different methods. These results suggest that the toxicity test using membrane fluidity is a highly useful and excellent method for toxicity testing as an alternative to conventional cytotoxicity testing.

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Since the mold cavity is exposed to the melting chamber in a two-chamber casting unit, the cavity is filled with Ar gas till casting of molten titanium. Thus, the gas evacuation rate immediately after melt casting must influence the castability and generation of internal defects. In this study, the cavity pressure was measured using a mold simulating a two-chamber casting process at room temperature and the results were converted into the casting pressure. Mold permeability and preset pressures in the melting and casting chambers were considered as factors influencing the quality of casting. The higher the mold permeability and the higher the difference between the preset pressures, the higher level the casting pressure rapidly reached. The results suggested that the choice of investment material should be made from the perspective of mold permeability suitable to the casting mechanism.

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