Change in compressive and tensile strengths, dimensional and weight change of glass ionomer cement("Chembond" and "Fuji-ionomer Type I") were observed in regards to the passage of time. Also, the surface of hardened cement was examined with SEM by means of replication technique and compared with polycarboxylate and zinc phosphate cements. Following results were obtained: 1. In respect to the compressive strength, those of "Fuji-ionomer" were largest regardless to the period of passed time. However, those of "Chembond" were similar to a zinc phosphate cement. 2. On the other hand, tensile strength of a polycarboxylate cement was the largest regardless to the period of passed time, followed by "Fuji-ionomer, ""Chembond" and a zinc phosphate cement in this order. 3. Bond strength of a polycarboxylate cement asw largest, followed by"Fuji-ionomer, ""Chembond" and a zinc phosphate cement. Although those tendencies were apparent up to 30 days, after this, similar bond strengths were obtained regardless to the type of cements. 4. As to the dimensional change under dry condition, similar contraction were observed with glass ionomer cements as a polycarboxylate cement.However, under wet condition, only glass ionomer cements indicated expansion.5.Decrease in weight of glass ionomer cements were intermediate between polycarboxylate and zinc phosphate cements under the dry condition.Contrastingly, apparent increase in weight was observed with glass ionomer cements. 6. From the SEM observation, it has become apparent that small cracks, appeared on the surface of glass ionomer cements, became more greater in width and depth after 1 day placement under dry condition.But, these cracks disappeared following 1 day placement under wet condition.

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Porcelain-fused-to-metal restorations are used extensively in restorative dentistry because of their strength, esthetics, and insolubility in oral fluids.The purpose of this study was to determine the favorable firing temperature of commercially available porcelain used in the porcelain-fused-to-metal system.The favorable firing temperature was evaluated using observation of surface texture and gloss, the tensile strength test, and observation of the interface between opaque porcelain and metal.The muffle of the porcelain furnace made in our laboratory was controlled by a computer to verify the working temperature.The following results were obtained:1.Opaque porcelain a)On Ceramco and Vita porcelains, surface gloss can be obtained by a firing temperature of 860℃, on the other hand, the Unibond porcelain, surface gloss cannot be obtained, but a slight color change does occur when a firing temperature of 900℃ is reached.b)By means of photomicroscopic observation of the interface between porcelain and metal, penetration of porcelain into the irregularities of the metal surface was observed at various firing temperature of 700℃, 750℃, 800℃, and 850℃.And from the E.P.M.A.analysis of the interface between Unibond porcelain and metal, the appearance of bonding between porcelain and metal at the interface was observed at a firing temperature of 850℃. c)From the tensile strength test, when the firing temperature was raised, a resultant increase in tensile strength was observed.2.Dentin and enamel porcelain a)In the case of Ceramco and Unibond porcelains, their surfaces had a granular texture, and a surface gloss was obtained by a firing temperature of 760℃;but the granular texture disappeared and smooth surface was obtained when a firing temperature of 790℃ was reached.On the other hand, the Vita porcelain surface had a granular texture, and surface gloss appeared at a firing temperature of 770℃;but the granular texture disappeared and a smooth surface was obtained by a firing temperature of 800℃.b)From the tensile strength test, when the firing temperature was raised, a resultant increase in tensile strength was observed.The results of this study indicate the most favorable firing temperature for opaque porcelain is 850℃;and for dentin and enamel porcelains, 760-780℃(Ceramco and Unibond)and 770-790℃(Vita).

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The Physicochemical properties of synthetic fluoridated CO₃-apatites were studied, The crystallinity of the apatitis showed similar patterns of variation with the degree of fluoridation analogous to the complex pattern of the fluoridated hydroxyapatites previously reported.The apparent solubility of fluoridated CO₃-apatites and dissolution rate of their pellets in acetate buffer solution at pH4.0 and 37℃ decreased monotonically with the degree of fluoridation in contrast to the unexpected crystallinity phenomena, and were extremely sensitive to acid at low fluoride content.

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Adaptation or dimensional deviations of the castings produced by Ni-alloys and phosphate bonded investments was evaluated by the ring-type castings fabricated by a direct technique for taking wax pattern and by sectioning the crown-type castings on the preparations embedded in resin.The correlation between dimensional deviations of the working dies for die-investing technique and dimensions of castings was also discussed.The findings were as follows:1)The phosphate bonded investments tested showed the sufficient expansion to compensate the castingshrinkage of Ni-alloy. 2)The observation of the sectioned specimens of the crown-type castings showed that the investing technique using the wax ring made an even space between the castings and the preparation.But the castings produced by the steel ring lined with petrol-jellyed asbestos or wet asbestos showed the restraint of the expansion at the line angle between the axial wall and the occlusal portion. 3)A high positive corrllation of the dimensional deviation was observed between the working dies and the castings in case of the die-investing technique by the phosphate bonded investments.

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In the present investigation, the physical properties of some commercially available composite resins for posterior teeth and visible light-cured resins were examined and compared with one conventional composite resin and one micro-particle filled resin, mainly on the basis of ADA Specification No.27 and ISO Specification No.4049.Soem additional testing procedures were also applied, and the resin/tooth interfaces were observed by EMPA.The following results were obtained:1.The filler contents of two composite resins for posterior teeth(Clearfil Posterior and KG)had almost the same value of one conventional composite resin(Clearfil FII), but one micro-particle filled resin for posterior teeth and three visible light-cured resins fell into the 31 to 63wt% range. 2.Only the water sorption of one visible light-cured resin(Visio Dispers)passed ADA Specification No.27, and the other seven composite resins had values increasing in the following order:KG, Clearfil Posterior, Clearfil FII, Isopast DS, Micro Jar, Heliosit, and Plurafil Super. 3.In the measurement of mechanical properties, eight composite resins passed either ADA Specification No.27 or ISO Specification No.4049. 4.In the measurement of compressive strength, three composite resins for posterior teeth showed values of more than 3, 000kg/cm² at 24 hours and were 30 to 60% stronger than one conventional composite resin measured at 28 days. 5.In the measurement of diametral tensile and transverse strength, three composite resins for posterior teeth and three visible light-cured resins were as strong as or weaker than one conventional composite resin tested. 6.The values of tensile strength at 6 months were almost the same as those at 28 days, and one composite resin for posterior teeth showed discoloration at this time which did not decrease its tensile strength.The discoloration occurred only at the surface of the specimen. 7.Concerning transverse strength values of three composite resins for posterior teeth, as the thickness of each specimen diminished, the values did not decrease;however, in the case of an extremely thin specimen, the value decreased exceedingly. 8.At the interface between each resin and enamel, none of the eight composite resins showed any gaps, but in the cavity floors of the dentin, almost all of the resin/tooth interfaces had gaps in them.

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The mechanical properties of pure titanium and titanium alloys were investigated in comparison with commercial dental casting alloys such as gold, nickel-and cobalt-chromium alloys for crown, bridge, plate and porcelain bonding.It was presumed that pure titanium was suitable for crown, bridge and porcelain bonding, 6%Al-4%V-Ti alloy for porcelain bonding and plate, and 13%Cu-Ti alloy for porcelain bonding.

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The heat-curing base resins cured by microwave heating and cured in a water bath or in a hot press were investigated on the surface roughness and the mold releasing property.The degree of the surface roughness of the base resins cured on the dental plaster mold by microwave heating was less about one-third than that of the resin cured in a water bath or in a hot pree.Further, the bonding strength between the dental plaster mold and the resin cured by microwave heating was approximately equal to two-thirds mold releasing strength between the dental plaster mold and the resin cured in a water bath.The surface of the resin cured by microwave heating was smoother than that of the resin cured in a water bath or in a hot press.Therefore, the specimen cured by microwave heating was easier to separate into the dental plaster mold and the cured resin than that cured in a water bath.Compared with the resin cured in a water bath or in a hot press, the resin cured by microwave heating had several advantages on surface roughness.

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In the previous study, it was found that the investment of magnesia cement which was widely used for industrial refractories is much more suitable for casting titanium than the conventional dental casting investments.The purpose of this study is to investigate the method or reducing the setting time of the magnesia investment for using as the convenient material in the usual dental casting method.The addition of potassium phosphate monobasic KH₂PO₄ or sodium bicarbonate NaHCO₃ reduced the setting time of the magnesia investment.The green strength of the magnesia investment also increased by the addition of 1% KH₂PO₄ or 0.5% NaHCO₃.

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It has been elucidated by a part of authors, Togaya and Ida¹⁾ that the investment of magnesia cement which is widely used for industrial refractories is extremely useful for dental casting of pure Ti metal rather than using a traditional phosphate bonded silica investment.However, the precise control of dimensional fitness between casting and abutment has been left unsolved.Excellent fitness of pure Ti casting(a type of full crown)to abutment was developed by the expansion of mold due to gas pressure generated by the reaction of added Al powder and alkaline aqueous solution in the investment.It was also experimentally confirmed that the generated gas bubbles do not depreciate the surface smoothness of castings.

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Clinically, the flow characteristics will govern the ease of mixing and handling and may affect the cavity wall adaptation.The flow characteristics of restorative composite resin pastes in the unset state were discussed by the viscosity vs.time curve and the shear stress vs.shear rate curve(the flow curve), measured with a cone-plate type rheometer.In the viscosity vs.time curve, viscosity was descreasing as the time has passed.In the flow curve, composite resin pastes showed hysteresis loops.These results show that composite resin pastes are thyxiotropic.

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Ca(OH)₂ has been used commonly as root canal filling material, liner and pulp capping material, and its pathological characteristics have been well studied previously.But its physical properties, which influence the handling of this material significantly, were not studied very much in the past.So, in order to accumulate fundamental data on the fluid behavior of Ca(OH)₂-H₂O system, the relation between shear rate and shear stress of this system was studied.Ca(OH)₂ and H₂O were mixed at the following rate:0.80g/ml, 0.75g/ml, 0.70g/ml, 0.65g/ml:and were measured at the temperatures 20℃, 30℃ and 37℃.When the Ca(OH)₂-H₂O system was given constant shear rate, the shear stress decreased gradually as the time elapsed.Then the shear rate was varied to 5rpm, 10rpm, 20rpm, 50rpm, and 100rpm, and the shear stress was measured respectively.From these result, a hysteresis loop was plotted according to Umeya's method, and the loop showed thixotropy.The strength of this flow increased as the amount of Ca(OH)₂ increased, and decreased as the temperature rose.Thixotropy was influenced largely by the amount of Ca(OH)₂ and slightly by the change of temperature.

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The biological effects of metals were studied by an organ culture method using chick embryo femora, of which usefulness was investigated to evaluate the biocompatibility of biomaterials.Wires of copper, iron, nickel(>99.99% purity), chromium(>98% purity)and cobalt-chromium alloy(40% cobalt, 20% chromium, 16% iron, 15% nickel, 7% molybdenum and 2% others)were processed to form test pieces of 0.30 to 0.35mm in diameter and 1.5mm in length.A pair of femora were excised from a 9-day chick embryo.The wire was inserted into the distal epiphysis of a femur and the other femur was used as the control, which were cultured at 37℃ for 7 days rolling at 15 rph.The growth and the differentiation of the femora were predominantly inhibited in the femora into which copper, iron or nickel wire was inserted.The femora with insertion of chromium or cobalt-chromium wire showed neither growth inhibition nor suppression of differentiation, although necrosis was observed in the tissue adjacent to chromium wire.The organ culture method using chick embryo femora can be applied for an easy and short-term test to examine the biological effects of biomaterials on the growth and the differentiation of animal tissues.

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The quantitative analysis of the casting porosity did not progress well compared with that of the mechanical properties.The quantitative analysis of the casting porosity of Au-Pd-Ag-Cu alloy was reported in the preceding paper.In this paper, the casting porosity of Ag-Pd-Cu alloy was analized.The polished specimens which were subdivided into equal sized pieces from the castings, were examined by use of the image analysis system connected to a metallurgical microscope.The size and the form of each porosity, and the distribution of porosities were measured.The main results were summarized as follows:The porosity ratio was influenced by the distance from a sprue.The difference between the porosity ratio of the central part and that of the marginal part was influenced by the casting process.There was a definite correlation between the porosity ratio and the maximum area of the porosity.The lower positive tangent count of the porosity was useful to determine the form of the porosity.There was a definite difference between the porosities of Au-Pd-Ag-Cu alloy and that of Ag-Pd-Cu alloy.From the facts described above, it was clear that the image analysis system was very useful to quantitatively determine the casting porosity.

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Change in compressive and tensile strengths, dimension and weight of specimens prepared from glass ionomer cements for luting were determined and compared to those of polycarboxylate and zinc phosphate cements.These specimens were maintained at 37℃ under dry oven or immersed in distilled water up to 12 months.The decrease in compressive strength was observed in a limited degree regardless to the type of cements even after the immersion in water up to 12 months.On the other hand, the eminent decrease in tensile strength was examined with glass ionomer cements.Change in dimension and weight of specimens terminated after a month regardless to the type of cements.

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The grain refinement effects of Ir and Rh added to an equiaxed crystal of Ag-based casting alloys were investigated.The results were as follows: (1)To refine the crystal size, similar to Ir-addition, the maximum amount of Rh added to pure Ag were about 0.005wt%.An addition of Ir or Rh over that maximum amounts caused the formation of white part(second phase)without the refinement of grain size. (2)Grain refinement effects are related to equilibrium distribution cofficient(K)of solute elements.K of Rh in Ag-Rh alloy is thought for much than 1. (3)The grain refinement effects of Ir or Rh added to an equiaxed crystal of Ag-Pd alloys were affected by Pd content of the alloy.A basic amount of Ir to Pd content was about 1/50 and those of Rh was about 1/100, but the mechanical properties did not improved of Ir or Rh-addition.An addition of excessive amounts of Ir or Rh to the alloy caused deterioration of the mechanical properties, especially reduce the elongation of the alloy.

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