Polishing of titanium castings was investigated using the newly developed centrifugal barrel polishing apparatus which has two unique characteristics such as a variable rotational speed (100〜1100 rpm) and a specific rotational ratio (N:n=4.5:1) of the turntable (N) and the barrel (n). The polishing efficiency at three kinds of rotational speed (500, 750, 1000 rpm) calculated by the centrifugal force and acceleration theoretically demonstrated the formation of the favorite sliding zone for the polishing at all rotational speed and the higher rotational speed was assumed to be more effective on this apparatus. This assumption was supported by the results where the weight loss (%) of titanium casting plates (15×10×2 mm) by barrel polishing with NR-3 were 0.06, 0.17 and 0.47 at 500, 750 and 1000 rpm, respectively.
Properties of each media for the titanium castings treated by #1500 were evaluated from the barrel polishing without water. NRT-6 and NR-3 were superior to other two media on polishing efficiency, but also found to form dull and irregular surface. On the other hand, although the weight loss of titanium plates by SA and TWG#12 were small, these media were effective to improve surface texture. Especially, the surface gloss polished by TWG#12 was remarkably high. The barrel polishing of titanium plates treated by carborundum was tried using these media in order (from coarse media to fine media) and the excellent surface with 0.63 μm (Rmax) and 441 (Gs20°) was obtained from a series of media (NRT-6, NR-3, SA, TWG#12). These results suggested that the barrel polishing using the newly developed centrifugal barrel polishing apparatus with dry media was effective for the polishing of titanium castings.

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The aims of this research were to clarify the potential role of a newly established human dental pulp cell line (LSC) to assess toxicological responses in the human dental pulp. The relative cytotoxicity of four dental resin monomers on LSC, MC3T3-E1 or L-929 cells was measured by MTT assay and PGE₂ release assay.
The resin monomers inhibited proliferation of LSC cells in concentration dependent manner. The ranking of the resin monomers according to their cytotoxicity on LSC cells was UDMA>BisGMA>TEGDMA>HEMA and similar to one obtained in L-929 or MC3T3-E1 cells. Their sensitivity to the resin monomers varied with the cell lines used. LSC and MC3T3-E1 cells were more sensitive to the resin monomers than L-929 cells in MTT assay. Four resin monomers caused enhancement of PGE₂ release in LSC and MC3T3-E1 cells. The effect occurred after 24 hrs exposure in lower concentration of the resin monomers. The ranking of the resin monomers according to their effects on PGE₂ release in LSC cells was UDMA>BisGMA>TEGDMA=HEMA. PGE₂ release in LSC cells represented a highly sensitive indicator for irritant effects of the resin monomers.
These findings suggest that LSC cells may be serve as an excellent cell line to evaluate the biocompatibility of restorative dental materials and toxicological events to the dental pulp.

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To clarify the thermal properties of a laminated structure during the restoration of a crown, specific thermal capacity and thermal diffusivity of laminated specimens compose of casting gold-silver-palladium alloy, porcelain and luting glass ionomer cements having each different thermal conductivity were measured by the Xenon-flash method.
From these experimental values, thermal conductivity were calculated and evaluated in comparison with each other. As a result, it was proven that when the specimen is composed of a laminated structure with different thermal properties, the value of thermal diffusivity was the most varied of all thermal properties. The larger the differences of both thermal diffusivity and conductivity became, the more changeable thermal properties became. A tendency for tehrmal conductivity to increase was noted in a laminated specimen in which thermal conductivity of input side was smaller than that of the output side compared to specimens with a reverse laminated structure.

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To determine the treatment state of surface treated silica, density, specific surface area and particle size were examined. As silane coupling agents, γ-Methacryloxypropyltrimethoxysilane (γ-MPTS), Vinyltrimethoxysilane (VTMS) and Vinyltrichlorosilane (VCLS) were used and the silica was treated under the wet process. These treated silica were separated by centrifugation and dried in vacuo. Then physical properties were examined. The effects of additional surface treatments for treated-silica, such as rinsing with Tetrahydrofuran (THF) or heat-treatment, on these physical properties were also examined.
Density and specific surface area were highly sensitive as a parameter for treatment state of surface treated silica. Therefore, the refection of these properties was comparatively clear in following areas: changes in the amount of deposited silane relative to increases in the concentration of the coupling agent, a decrease in the deposited silane due to the rinse-treatment or changes in the adsorption state due to rinse-treatment and heat-treatment. However, particle size was thought to be a less sensitive parameter, because it showed little change in this study.

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The strength of adhesion between tooth substance and composite resins, used as restorative material, was assessed by a push-out shear test, which simulated the force produced by mastication. A cylindrical cavity was created in each of four kinds of tooth substance. The cavity was then filled with composite resin. The test specimens prepared were then pressed to examine the adhesive strength of composite resin. The adhesive strength was highest for enamel, was lower for enamel/dentin and was lowest for dentin. The adhesive strength of enamel/dentin was much lower than that of enamel (45% lower when chemically-cured composite resin was used, and 29% lower when light-cured composite resin was used). This was probably because the adhesive area between the dentin reduced the adhesive strength. We then analyzed samples in which shear force was applied to the enamel/dentin test specimen. The apparent adhesive strength, obtained form theoretical calculation, tended to show a constant relationship to the strength actually measured. This suggests that the effective adhesive area of the dentin is smaller than area actually covered by the dentin. Furthermore, a gap, probably due to the effects of tensile stress, was observed in the adhesive interface between the composite resin and dentin. This gap seems to reduce the adhesive area, leading to a decrease in adhesive strength. Thus, the push-out shear test method appears to be useful in evaluating adhesive properties of composite resin.

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This study is to evaluate the titanium castability with an all-directional pressure type casting machine, using two kind of phosphate bonded investments which have different gas permeabilityies. The pure titanium used was JIS grade 2. A mesh grid type pattern was used to measure the castability. An all-directional pressure type casting machine (AUTOCAST-HC III: GC Co.) was employed in this study. Two types of phosphate bonded investment were tested. The two materials were invested, heated and cast according to the manufacturer's instructions. Casting was performed with the mold at room temperature in both cases. Seven different sizes of mold diameter 25, 30, 35, 40, 45, 50, 55, 60mm were prepared for T-INVEST, and five 25, 35, 45, 55, 65 mm for T-INVEST C & B, respectively. Distance from the bottom to the pattern of the mold was 10, 20, 30 mm on each investment. It was concluded that a high percentage of castability (over 90%) was gained, when the mold diameter was increased with T-INVEST. Mold diameter at T-INVEST showed a significant (p<0.01) correlation to the castability. Furthermore, with T-INVEST C & B, high castability (over 90%) was shown under every condition. The change in distance change from pattern to bottom of the mold was not effective. This result seemed to be caused by non uniform contact between the bottom of the mold to the casting table. These results indicate that high performance of castability on titanium was achieved when gas permeability was decreased using an all-directional pressure type casting machine.

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Carbonate-contatning apatites prepared from aqueous media were sintered for 2 hours at various temperatures after they had been isostatically compacted at 600 MPa. Comparion of scanning electron microgaphs of sintered specimens suggested that specimens with over 8 wt% carbonate could be successfully sintered at temperatures between 650 and 750℃. The gas-chromatograph analysis of carbon dioxide that evolved from specimens during pyrolysis suggested that these specimens still contained approximately half the amounts of carbonate initially present. These estimated amounts of carbonate agreed to those directly measured by infrared spectroscopy. Apatite specimens containing 11.8 wt% carbonate sintered at temperatures between 650〜750℃ contained approximately 6 wt% carbonate, which is quite close to the typical amount of carbonate in human bone. These findings strongly suggest that compared to sintered hydroxyapatite, sintered carbonate-containing apatites are more useful as bone substitute materials, since they closely resemble bone apatite.

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Mechanical properties of titanium-zirconium binary alloys were investigated in order to reveal their possibility for new biomedical materials. Useful data for alloy designing are collected through a tensile test and an optical microscopy. The strength of the alloys containing 25 to 75 atomic per cent zirconium is approximately three times as large as the strength of pure titanium and pure zirconium. These results consist wtih the results of other investifators and hardness test reported previously. Large elongation are obtained regardless of strengthening by a solid solution hardening and/or a precipitate hardening in the alloys having 25 to 75 atomic per cent zirconium content. From these reults, it is concluded that new alloys for biomedical materials should be designed as a titanium-zirconium base alloys.

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