Mechanical properties, including tensile strength, proof stress, elongation and hardness of wrought titanium material standard and casting titanium materials (JIS class 1〜JIS class 4) were measured under the same conditions, and findings were compared. The result showed that from JIS class 1 to JIS class 4, the data deviation from wrought material, in respect of tensile strength, decreased 50%, proof stress 10〜40%, elongation 20〜50%. Compared with JIS class 1 titanium material, JIS class 4 titanium materials were better in both tensile strength and proof stress. This may result from the influence of trace elements. Especially the oxygen content, as shown in EPMA surface analysis, prominently influenced the mechanical properties.

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Effects of fissure sealants on differentiation of mouse embryonic stem cells were tested using the embryonic stem cell test (EST), which consists of three parameters, differentiation rate into contracting myocard, 50% cell viability of ES-D 3 cells and of Balb/c 3 T 3 cells, as calculated by a designated formula. Of four resin-based materials and two glass ionomer cement materials tested, 50% inhibition of ES-D 3 cell differentiation (ID₅₀) values ranged between 6.4 μg/ml and 9.2 μg/ml for resin-based materials. On the contrary, the liquid of glass ionomer cement, Fuji III showed an average of 157.3 μ/ml, whereas Fuji III LC showed an average of 54.1 μg/ml. Fifty percent inhibition concentration (IC₅₀) values of ES-D 3 cells and 3 T 3 cells were in a range similar to that of ID₅₀ values. However, the powder of glass ionomer cements did not yield ID₅₀ and IC₅₀ values. Regarding the effect of hardened materials on the tissue model (Toyobo),the resin-based materials showed more severe cytotoxicity than glassionomer cements. It was demonstrated that four resin-based fissure sealants were ranked as weak embryotoxins by EST protocol, whereas liquid of glass ionomer cements were not. It is considered that further intensive study on the embryotoxicity of dental biomaterials is needed from the perspective of biological safety.

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A thiirane bifunctional monomer, 3, 4-epithiobutyl 2, 2-bis (methacryloyloxymethyl) propionate (EP2BMA), was employed as an adhesive bonding promoter for precious metals. Two surface-treatment agents for precious metals were prepared by dissolving EP2BMA in ethanol. Gold alloy, gold-silver-palladium alloy and silver alloy were used as an adherend. Mirror-finished alloy surfaces treated with the agents were allowed to stand for one day and then washed to remove excessive monomer when the thiirane concentration was high (1 mol %). Two alloy specimens were butt-jointed with MMA-PMMA resin and tensile bond strengths were measured after 2,000 thermal cyclings, followed by observation of the fractured surfaces after tensile test. The surface treatment with EP2BMA significantly improved bond strengths. The effect of EP2BMA was comparable to that of 9, 10-epithiodecyl methacrylate (EP8MA) when TBBO was employed as an initiator, while the bond strength to silver alloy treated with EP2BMA was considerably lower than that with EP8MA in the case of BPO-amine initiator.

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This study evaluated the usefulness of light-curing trial base resins (LCT) for maxillary complete dentures compared with conventional self-curing trial base resins (SCT). Three commercial LCTs and two commercial SCTs were measured in terms of flexural properties, Knoop hardness number (KHN), dimensional change after curing, filler content and fit to the model. Flexural properties and KHNs of LCTs varied among products, and some of those were influenced by the thickness of the resin plates. The flexural properties, especially flexural moduli, and KHNs of LCTs were significantly greater than those of SCTs. However, the deformations at central portions of the model of LCTs were significanatly bigger than those of SCTs. These results suggest that LCT is useful for a trial base plate resin of maxillary complete denture because of its adequate mechanical properties and easy manipulation despite the slight greater deformation.

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This study investigated changes in hardness of glass lonomer cements for luting during the setting stage up to one day. Two different conventional and two different resin-modified glass ionomer cements were tested. The cements were mixed according to the manufacturers' instructions at three different mixing ratios. The Knoop hardnesses of the surface of the cement specimens were determined 10 minutes after the start of mixing up to 24 hours. Increases in the mixing ratio increased the hardness of all cements during the measured period. The hardness of the conventional glass ionomer cements increased up to the first 15 minutes; however, there were no changes in the hardness values from 20 minutes to 6 hours after the start of mixing. The hardness values of the resin-modified glass ionomer cements increased during the initial setting period. The hardness of glass ionomer cements markedly changed while the setting reaction proceeded.

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