The effect of air-vent system on microstructures in low-melting 32 Ni-23 Cu-25 Mn casting alloy was investigated in this article(Part 2), and it was examined which air-vent systems were optimum to the homogeneity of microstructures. As a result, three kinds of crystal grains as dendritic grain noted by A-grain, disk-like grain(B-grain)and large-sized grain(C-grain)were observed for three different air-vent systems. On the contrary, the formation of C-grain was uniform at the surface layer of casting specimen and the grain size of C-grain distributed uniformly over casting specimen which had 45 degree-sprue and blind-type air-vent system. Therefore, it was clarified that the optimum air-vent system corresponded to blind-type air-vent system in 45 degree-sprue case.

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The microstructure change due to various air-vent systems in dental 84Ni-9Cr casting alloy was, similarly to the article(Part 2), investigated. As a result, cell structures which indicated equiaxed and cell-like morphologies were found at the interior and superficial layers of casting specimen in using both blind-type and closed-type air-vent systems at the 0 degree-sprue. On the contrary, cellular dendritic and cell structures which were observed in 45 degree-sprue and blind-type air-vent system, formed at the interior and superficial layers of casting specimen, respectively, which showed morphologically inhomogeneous distribution. Examining the shape and the size distribution of microstructures, the distribution of equiaxed and cell-like cell structures at 0 degree-sprue and blind-type air-vent system showed, independent of portions of casting specimen, the homogeneous state having approximate 20μm as average value. The cell-like cell structure at closed-type air-vent system(0 degree-sprue system)had, however, the inhomogeneous distribution at the superficial layers. In addition, arm length of cellular dendritic structure at 45 degree-sprue system ranged from 100 to 500μm near the sprue portion where had larger values than the other portions of casting specimen. Considering the corrosion property, cellular dendritic structure which showed strong Ni-segregation was heavily attacked and this corroded area was very larger than cell structures. Therefore, the blind-type air-vent system at 0 degree-sprue in high-melting 84Ni-9Cr alloy was optimum, which was different from the Ni-Cu-Mn alloy having the 45 degree-sprue and blind-type air-vent system as an optimum vent system.

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The present studies, as basic studies purposing to clarify the condensability of amalgam mix using a spherical alloy and a lathe cut alloy, examined the effects of various manipulative conditions. For the studies, a condensation apparatus for measuring the condensability, which makes it possible to measure the condensation height during operation, was contrived and applied.
The following results were obtained.
(1)The change of condensability became stable according to the increase of the number of thrust, and when the thrust number exceeded 75 or 100, it became almost fixed.
(2)The mixing time and the size of amalgam mix had little effects on the condensability.
(3)The mercury-alloy ratio, the starting time of condensation, the condensation pressure, the size of plugger in diameter and the cavity-plugger's area ratio had effects on the condensability.The effects were remarkable especially in the case of spherical alloy amalgam.
(4)Under the same condensation pressure, spherical alloy amalgam showed smaller condensability as compared with lathe cut alloy amalgam.

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The present studies are concerned with the soluble elements, properties of set cement surface and its elemental analysis of dental cements in distilled water.Zinc phosphate cement is soaked in distilled water for a day, the soluble elements are Zn 4.2μg/cm², and Mg and Ca, respectively 2.9 and 0.4μg/cm².Again, in the case of 7 days soak, the author presumes that zinc phosphate is separated as crystals, approximately 10μm, on the surface, judging from the EPMA's face analysis.
The amount of solubility of Zn of carboxylate cement, both in a day and 7 days soak case, is comparatively small, but Mg, in both cases, shows large values, resp ectively 2.9 and 26.2μg/cm².
The amount of solubility of silicate cement is in the case of a day soak, Na shows a large value, 247.1μg/cm², which reaches 340.2μg/cm² when soaked for 7 days. Again, Si and Al, in the case of a day soak, respectively show 33.0 and 36.1μg/cm², which increase in the case of 7 days soak.

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Change in mechanical properties and microstructure of 7 commercially available amalgams (2 conventional, 4 high copper and 1 fluoride containing) immersed in water up to 12 months was examined.
Slight increase in compressive strength and also slight decrease in diametral tensile strength was observed in any case except for fluoride containing amalgam.With fluoride containing amalgam, eminent decrease in both compressive and diametral tensile strengths were observed.
Any change in static creep was also observed with amalgams except for the apparent increase in both lathe-cut conventional and fluoride containing amalgams. Apparent change in microstructure were observed with these two amalgams, indicating some relation with altered physical properties.

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Physical properties of a high copper amalgam containing tannin-fluoride preparation and its alteration following immersion in water up to 12 months were examined in relation to its microstructure.
Any eminent effects were observed on the physical properties of resultant amalgam in regard to the admixed ratio of tannin-fluoride preparation up to 0.5%.However, apparent influences were observed at 1.0 wt%.
Effect of water immersion was apparent with the reduction of diametral tensile strength of amalgam containing 1.0 wt% tannin-fluoride. Remarkable change in compressive strength and static creep was not observed. Microstructural change was observed on amalgam containing tannin-fluoride regardless to its admixed ratio.

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The solubility of casted silver in various corrosive solutions in different thermal and periodic conditions was measured by means of an atomic absorption analyzer. Three factors (solution, time and temperature) and levels were selected.By design of experiment, 27 specimens were assigned using L₂₇(3¹³)table of orthogonal arrays.
The amount of dissolved silver was slight as about 0.03 mg/cm² in maximum.The factors selected were all significant. The slolution was the most decisive factor to the silver dissolution. At three month period, silver dissolved significantly most in NaCl solution, and least in the artificial saliva. No significant thermal and periodic effects were observed in the artificial saliva, while the thermal effect at 60℃ was noted in 1% lactic acid solution. The periodic effect at 3 months was revealed in NaCl solution.

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Ni-45wt% Ti(Ni-50at% Ti) alloy was cast into Magnesia cement molds and phosphate-bonded investment molds, using an Argon-arc pressure casting machine and a Cu crucible.
The castings (bars) by Magnesia cement molds have larger elongation and rougher surfaces, than those by phosphate-bonded investment molds.
All castings bent at 0℃ showed shape memory effect. Some of the castings were broken on bending at 0℃.

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The problem of the concavity, which occurred on the corner of the inner surface of cast crown, was studied using a K metal under various casting conditions.
1)The incomplete castings and the concavity were eliminated for thick sprue, high mold temperature and many turns of the spring, in the case of a gypsum-bonded investment and centrifugal casting.
2)In the case of a phosphate-bonded investment and centrifugal casting, the concavity was eliminated at higher mold temperature, than in above-mentioned case.
3)No concavity occurred in pressure casting (air pressure:4kg/cm², pressing time: 30 sec), in spite of a phosphate-bonded investment and low mold temperature.
4)The incomplete castings and the concavity occurred for a short pressing time in pressure casting.

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Surface defects of cast Ni-Cr crowns were studied using various casting machines.The following conclusions were obtained;
1)The defective castings with surface roughness were formed, when a gypsum-bonded investment was used.
2)The concavity on the inner surface of cast crown occurred at low mold temperature or in short holding time, when a centrifugal casting machine and a phosphatebonded investment were used.
3)No concavity on the inner surface occurred in spite of low mold temperature or short holding time, when a pressure casting machine and a phosphate-bonded investment were used.
4)In another pressure casting machine, the air in the mold was vacuumed and then the whole surface of cast ring was pressed by Argon gas.No concavity on inner surface and large surface concavity on outer surface occurred, when this casting machine and a phosphate-bonded investment were used.

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The purpose of this investigation was to clarify thermal behavion of dental amalgam.In this investigation, the effect of temperature on the transitions of the γ₁, γ₂ and β₁ phases was clarified by using X-ray diffraction analysis.
The obtained results were as follows:
1.For low copper amalgam, the peaks of the γ₂ phase disappeared into the background at about 73℃.
2.The γ₁→β₁ transition was affected more remarkably by the temperature than by the time elapsed from start of trituration.
3.In case of rising temperature, the peaks of the β₁ phase appeared at about 73℃ in both high and low copper amalgam. Contrary to this, the peaks of the γ₁ phase disappeared in high copper amalgam at higher temperature than in low copper amalgam.
4.In case of falling temperature, the peaks of the γ₁ phase appeared at about 40℃ in low copper amalgam, but between 60 and 70℃ in high copper amalgam.

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Weldability of polysulfone had been studied and possibility of the welding had been already clarified.Namely, it was made clear that welding strength of P.S.F. was expected to be twice as much of adhesion strength by self-curing resin, and that a welding method to prevent occurrence of bubbles should be developed, since considerable number of bubbles existed in the weld of P.S.F. Study to develop a welding method whereby occurrence of bubbles is suppressed has been made, and satisfactory result of the study is reported hereunder. As a means of bubble-free welding, preparative drying was adopted.Specimens in the size of 10×10×2 mm. were cut out of P.1700 NT made by Nissan Chemical Co. Specimens were adjusted to condition at 20℃ for 48 hours, either in a desiccator or in saline solution;thence they were preparatively dried for 0.5-24 hours at 100-160℃ by a fixed temperature blower-dryer (DK 42 type made by Yamato Kagaku). These results lead to the conclusions as follows:It was found that occurrence of bubbles at the weld of P.S.F. can be prevented by preparative drying at 160℃ for 3-3.5 hours.

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In order to accumulate the fundamental data for discussing the shrinkage in dental castings, the density of pure gold, silver and copper was measured at a temperature ranging from room temperature to about 1400℃, by using the apparatus which was based on the Sessile drop method. Thermal shrinkage in liquid, during freezing, and in solid state were determined individually from the temperature dependence of density measured under a condition as free from surrounding materials as possible.
The decrease of volume during freezing were 5.2% for gold, 5.0% for silver, and 4.9% for copper, respectively. From these conclusions the shrinkage in dental castings was discussed throughly.

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The purpose of this study was to evaluate the water uptakes and solubilities of 28 kinds of various dental filling composite resins by the method of ISO(TC106, WG1/TG9).Furthermore, the solubilities in )organic solvents[ethanol:H₂O(7:3), tetrahydrofuran: H₂O(9:1)]were examined.
The following results were obtained.
1)It was found that the solubility of dental filling composite resin was generally related to its water uptake (i.e.the greater the value of water uptake, the greater the value of solubility). And the inorganic filler composite resins showed less water uptakes and solubilities than the organic filler composite resins.
2)In this study, the water uptakes and solubilities of dental filling composite resins were not affected by the surface property, namely polished or not, except in the case of lightcured type composite resins.
3)When dental filling composite resins were extracted by 600 ml of water using Soxhlet's method at 85℃, for 48 hours, the values of solubility were commonly greater than those abtained occording to ISO (TC 106, WG 1/TG 9).
4)In addition, when the dental filling composite resins were extracted by 5 ml of ethanol:H₂O(7:3)or 5 ml of tetrahydrofuran: H₂O(9:1)mixed solvents at 37±1℃ for 1 week, it was observed that the values of solubility in the latter were greater than those of the former. But some organic filler type composite resins showed no weight loss after extraction by both organic solvents when they were placed in a dessicator as the method proposed by ISO.
5)The filler embedded in composite resin was observed by SEM after any extraction.

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