Antibacterial activity of Ag-silica glass, composite resin filled with Ag-silica glass and silver glass ionomer cement was measured in vitro.Ag-silica glass was prepared by the sol-gel method, and composite resin was mixed in the ratio of resin in Ag-silica glass was 70%.Ketac-Silver and Ketac-CEM were used for this experiment.S.mutans was anaerobically cultured in TSBY at 37℃ for 10-12h.Then bacterial cells were adjusted to a concentration of 1×10⁶cells/ml.Each sample was incubated in this fluid.The number of surviving cells was estimated by culturing on TSBY agar plates.The concentration of silver ion released from composite resin or Ketac-Silver was determined using an ICP.Ag-silica glass and composite resin filled with Ag-silica glass showed significant antibacterial activity.Ketac-Silver also showed antibacterial activity.The number of surviving cells was decreased in proportion to the increase in silver ions released from silver ionomers.

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Dimensional change was measured when five kinds of fading alginate impression materials were immersed in six kinds of electrolyzed acid waters or HAIKUROSOFUTO oxidized water.All alginate impression materials were expanded immediately by immersing into each of the solutions.Powdered materials were continued to expand in HAIKUROSOFUTO oxidized water, and were shrunk in electrolyzed acid waters.The effects of varieties of alginate impression materials on dimensional change were stronger than those of varieties of function waters.Disinfection was investigated when an alginate impression material with adherent or intermixed Escherichia coli was immersed in either an electrolyzed acid water or HAIKUROSOFUTO oxidized water.E.coli adhered to the surface of the impression material was killed by immersion in the solutions for one minute.However, when dental stone was flowed on the disinfected surface of the impression material, a few E.coli were observed on the surface of the stone.Disinfection was not achieved for the intermixed bacteria at 1mm from the surface of the impression material.

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We developed a new replica method using a new type of trial-manufactured resin(Kuraray, Japan).Although many replica methods for evaluating the surface texture of intra-oral restorations have been reported, almost all methods are involved two steps.However, this new method involves one step.The advantages of this method are simplicity of handling and time saving.The disadvantage is that it is a negative replica and therefore a reverse image.To address this issue, a two step method was also developed.We tried to investigate the reproducibility of form and size of these methods by SEM observation while measuring surface roughness. As compared with the conventional method, the results were as follows.1.All three methods showed similar size reproducibility.2.According to SEM observation, this new one step method had good form reproducibility.3.This new one step method was useful for evaluating the texture of intra-oral restorations.

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Surface roughness of stone models obtained from agar impressions and agar/alginate combined impressions with various agar layer thicknesses was measured.Diameters of dies from the combined impressions were also measured.Six brands of agar impression materials were used for the combined impression systems.In three brands, the surface roughness was decreased in the stone models from combined impressions compared to those from agar impressions.Although surface roughness decreased with decreases in agar layer thickness, the dimensional accuracy of the stone dies was not affected by changes in the agar layer thickness.

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To realize computerized porcelain forming, it is necessary to scientifically analyze and mechanical reproduce every casual forming procedure carried out by technicians.Wetness of porcelain slurry during forming is one of the highly influential factors affecting the quality of work.But there seems to be no definite standard for wetness evaluation.To develop automatic control of porcelain wetness, this study examined evaluation of the wetness by image processing.The relationship between porcelain wetness and strength of reflected light from its surface was measured using an experimental system.The strength of reflected light increased as water was supplied to dry porcelain powder.The strength decreased as the porcelain was dried subsequent to wetting.Strength of reflected light was influenced by condensation and the quantity of porcelain powder.

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The orthodontic force of the new expansion appliances made from super-elastic Ti-Ni alloy wire was investigated in comparison with that of quad-helix appliances made from Co-Cr alloy.Shape memory treatment was achieved by the first treatment at 713K for 1.8ks and the second one at 753K or 793K for 1.8ks.Transformation temperatures and the orthodontic force of the appliances were examined.As a result, the load changed linearly with displacement for the Co-Cr alloy specimens, while there were zones where the load was less changeable for the Ti-Ni alloy ones.The load level of the Ti-Ni alloy specimens was in the same range as those of the Co-Cr alloy ones.The load hysteresis was less when treated at 753K.Therefore, the application of Ti-Ni alloy to orthodontic expansion appliances makes it possible to utilize continuous, stable, safe and effective force in orthodontic treatment due to the super-elasticity.

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The cumulative weight losses of titanium plates when they were immersed in six KHF₂-LiF-NaCl-KCl fluxes were measured to examine the reaction of titanium.Spreading areas of a silver solder were determined using these fluxes.The cumulative weight loss of titanium increased with the increasing immersion times at 900℃ for all fluxes.The reactivites of the fluxes were promoted in the order of[NaCl+KCl]<[56KHF₂-14LiF-30(NaCl+KCl)]<[50KHF₂-50LiF]<[70KHF₂-30LiF]<KHF₂<LiF.Temperature also affected the reactivity.The activation energy was 19.5kcal/mol in the initial reaction between titanium and[56KHF₂-14LiF-30(NaCl+KCl)].The spreading areas of solder increased in the order of[NaCl+KCl], [70KHF₂-30LiF]<KHF₂<[50KHF₂-50LiF], [56KHF₂-14LiF-30(NaCl+KCl)], except LiF.The spreading of solder hardly occurred for LiF.The reactivity of the fluxes was not always consistent with the increase in the spreading areas of solder.

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Due to recent technological advances, dental casting of titanium seems to have reached the stage of practical application.Fatigue test is requisite for the application of titanium as a dental casting material in addition to tensile test, hardness test, etc.Furthermore, corrosion fatigue test is more suitable considering the actual oral environment.In this study, corrosion fatigue test equipment was developed, with which the corrosion fatigue property of titanium was investigated in 0.9% NaCl solution.As the result, it was suggested that the corrosion fatigue property of dental material could be evaluated effectively with this system, and that the corrosion fatigue property of titanium was good as a dental casting material.

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Experimental primers consisting of 6-[N-(4-vinylbenzyl)propylamino]-1, 3, 5-triazine-2, 4-dithione(VBATDT)or both VBATDT and 10-methacryloyloxydecyl dihydrogen phosphate(MDP)in acetone were prepared to promote adhesion of resin to dental metal.After surface treatment with the experimental primer, composite type resin cement, Panavia 21(Kuraray), was applied, and the adhesive strength was examined.Adhesion-promoting effect of the primer containing both VBATDT and MDP instead of VBATDT alone was observed for precious metals such as Ag, Pt and Pd, and base metals such as Cr and Ti.After the primer with VBATDT and MDP was applied and dried, bond strength was higher at a VBATDT concentration of 0.1 or 0.5wt% than that at 5.0wt%, when the concentration of MDP was kept at 1.0wt%.It was further indicated that a suitable concentration of MDP was around 0.2〜0.5wt% on the basis of the test where VBATDT was constant at 0.5wt% and the concentration of MDP was altered.

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In this paper, the testing method of mode I fracture toughness for a dental adhesive resin was investigated varying the dimension of test specimen as a factor by using double cantilever beam(DCB)testing in which the test specimen had a metal/adhesive resin/metal construction.The major findings were as follows.In all test specimens, it was found that the values of fracture toughness(G_IC, G_IR)at the process of crack propagation were nearly constant.Therefore, it was found that the fracture toughness(G_IC)at maximal load might only be measured to evaluate an adhesive resin. On the values of G_IC, there was no effect from the dimensions of the test specimen, width(b=3, 5mm), thickness(2h_m=2, 4mm)and initial crack length(a₀=9-19mm).Such a testing method is more effective for evaluating the adhesive property of a adhesive resin.

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Titanium castings were prepared in two atmospheres;one was argon-arc melted and cast in the ambient atmosphere(AA)and the other was argon-arc melted and cast in the argon-replaced atmosphere(ARA).Tensile test and Vickers hardness measurement were conducted.The results were discussed in relation to the contents of oxygen and nitrogen absorbed by titanium during the melting and the casting procedures.While the tensile strength and the hardness of castings obtained in AA were higher than those of castings obtained in ARA, the elongation exhibited the reverse relation.The oxygen content was ranked from least to most:the ingot, the solidified and the cast.The oxygen content of the solidified and the cast obtained in ARA tended to be higher than that of castings obtained in AA.On the contrary, the nitrogen content of castings obtained in AA was 13 to 15 times higher than that of castings obtained in ARA.The results of this study indicate that the nitrogen content relates to the above-mentioned difference in mechanical properties of castings obtained in AA or ARA.

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