To investigate the difference in castability between pure titanium and Ti-6Al-4V alloy, three types of casting that differed in mold filling type were constructed.Casting defects were checked by X-ray transparencies and flow behavior was observed using the molten tracer element method.There was no difference between the two metals for F type fillings.However, for thin cavities(W type fillings)and mesh cavities(B type fillings), the castability of the titanium alloy was slightly lower than that of pure titanium.The thermal properties of the titanium alloy are presumed to be considerably different from those of pure titanium since platinum, one of the tracers, was hardly detected during mesh casting of the alloy.Microanalysis of the top of the mesh casting revealed that the molten alloy flow included many particles.In conclusion, the reason for the poorer castability of the titanium alloy is that the viscosity of the molten alloy increased significantly because of the solidification particles included in its flow.

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This study investigated antibacterial activity of tissue conditioners containing bamboo extract on Candida albicans.Then the effects of bamboo extract on the hardness and wettability of tissue conditioners and the attachment of Candida albicans on tissue conditioners were studied in vitro.When tissue conditioners containing bamboo extract were immersed in Heart infusion(HI)agar medium, the bamboo extract scarcely eluted.Neither hardness nor wettability(contact angle)were significantly affected by additing to up to 10wt% bamboo extract to tissue conditioners.The adhesion of Candida albicans on tissue conditioners containing 10wt% bamboo extract was significantly inhibited.

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Delayed seating of an alginate mix on agar in conventional agar/alginate impression systems causes a failure of adhesion between the agar and alginate.To solve this problem, an improved impression systems using an adhesive(cyanoacrylate)on the gelled agar was developed.The bond strength and dimensional accuracy of this system were measured on combinations of 3 agar and 4 alginate impression materials.The bond strength was increased by applying adhesive to the gelled agar.The dimensional accuracy of dies obtained by this improved system was clinically acceptable.

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Titanium exhibits unique mechanical properties compared to those of other metallic materials.In this study, the stress-strain diagram of titanium casting was proven to be significantly affected by specimen diameter.In particular, total elongation increased markedly with increasing diameter.As for the referential result on a cobalt-chromium alloy, the factor affected the mechanical properties much less than titanium, though the distribution of casting defect was influenced considerably.It was suggested that thermal capacity affected the coagulated microstructure of titanium, which influenced the change in elongation due to the peculiar deformation mechanism of titanium.Since titanium is easily affected by various factors, the mechanical properties of titanium castings should be evaluated with detailed consideration of the specimen configuration, casting conditions, etc.

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We examined the effects of nitric acid and heat treatments on titanium and Ti-6Al-4V alloy by measuring the dynamic contact angle, relative cell adhesion rates after 1 hour and 24 hours, and the cellular adhesive strength of L-929 cells using a cone and disk type viscometer.The dynamic contact angle was not influenced by 40% nitric acid, but was decreased by heat treatment.The relative cell adhesion rate after each treatment remained the same as the control value except for that after 1 hour treatment at 800℃.The percent of adherent cells decreased with longer application of shear stress.However, there was no difference in the percent of adherent cells with changes in the experimental conditions.Thus, a method other than contact angle should be used to evaluate cell adhesive strength.

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The chevron notched beam(CNB)method was used to evaluate the fracture toughness(K_<IC>)of porcelain for metal ceramics.Compliances were calculated using Bluhm's slice model, and the effects of notched shapes, span ratios and cross head speeds were examined by four point bending mode in Ar gas.Results indicated that K_<IC> was only slightly affected by these factors.In particular, the absence of dependence on cross head speeds supports that, in Ar gas, stable crack growth did not occur near the maximum load.The averaged K_<IC> was 1.11±0.08MPam^<1/2>, although slight increase, as considered due to R-curve behavior, was observed with increase of crack length at the maximum load.The fracture energy calculated from both K_<IC> and Young's modulus was about 8.9±0.7J/m^2.These measurements suggest that the CNB method is a simple technique than the SEPB method and useful for evaluating the K_<IC> of dental ceramics such as porcelain.

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The author examined composite ceramics precipitated a whisker to obtain biomaterial with excellent mechanical properties by adding a diopside consisting of crystallized glass to hydroxyapatite(HAP)which is known as a highly biocompatible material.The author compared this composite ceramics with HAP and diopside with regard to mechanical properties and tissue irritation.In conclusion, the diopside and the composite ceramics were significantly stronger than HAP.In particularly, the composite ceramics(60vol% diopside)was approximately three times stronger than HAP, but the mechanical strength of all materials examined had a tendency to decrease gradually over long-term storage in saline.Concerning tissue irritation, the diopside and the composite ceramics showed the same biocompatibility as HAP.Therefore, 60vol% diopside and diopside alone may be useful as bone filling materials and for dental implants.

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