The casting of a comparatively large-sized frame for denture was tested by connecting the large casting-ring especially designed for new vacuum casting apparatus in this study.
The following results were obtained:
1)The casting of the metal frame for full or partial dentures was possible and had few failures with this technique. An extremely smooth casting especially at the outer surface was obtained.
2)The reason why this vacuum casting-procedure made it possible to produce these large castings was conjected as follows: Avoiding the leakage of air which tended to occur at the gap between the casting-ring and investment by covering the casting-ring, the improvement of exhaust efficiency by means of negative pressure from the bottom and the side of the mold occurring simultaneously and the quick attainment of sufficient pressure difference between the top and the inside of the mold.

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The air turbine handpieces are usually used for the superior instruments to cut tooth effectively. And recently the air turbines become to be used for the dental techniques as to be called the air motors.
In this paper, we studied the torational performance test method of the air turbine handpieces which are applied at the constant feed speed cutting systems and the constant load ones. Both cutting systems are usually applied the dental practice and technical work and the rotational performance of the air turbines are considered to be different with these cutting systems. And having the results of these rotational performance test method, we tried to examined the rotational performance of the air turbine handpieces with the different supporting systems, that is, the air bearing type and the ball bearing type systems.
So, we made the experimental apparatus of the rotational performance test which have the both leading systems respectively. And we obtained the rotational speed and torque diagram that are the coincident the results of the both loading systems. Therefore the constant feed speed test method which are easy one are known as a good test method to examined the rotational performance of the dental air turbine handpieces. And then using the constant load testing method, we studied the relations between the rotational performance and the supporting method of the rotational components. The supporting method of the air turbine handpieces are usually used with the air bearing type and ball bearing one. So we tested the rotational performance of air turbines concened with the both supporting methods. During the loading of the air turbines, the rotational speed of the air bearing type turbine suddenly go down at that point of the ratio of the rotational speed down about 40%. But the ball bearing type turbines are continuing to be rotated at that point.Therefore the air bearing type turbines have a large rotational speed ranges to be changed. But the air turbines with the air bearing type supporting systems have a lower torque than the ball bearing air turbine handpieces.

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The castability in dental 32Ni-23Cu-25Mn and 84Ni-9Cr cast alloys was examined, using the coil-type cast mould patterns with spiral-like and up and down-like shapes.In case of the spiral coil-type specimen having 1.0mm diameter in the alloys, the castability was not effected notably by the crucible form and the sprue position.The value(about 89%)in the low-melting 32Ni-23Cu-25Mn alloy became twice more than that(approximately 40%)of the high-melting 84Ni-9Cr alloy.On the contrary, the castability of the coil-type(up and down)mould pattern in the low-melting alloy decreased when a diameter in coil-part had a larger value than that in sprue-part of the cast specimen.Namely, when the value of(d_c/d_s)² varied less than 1.0, the castability had the approximately constant value but tended to decrease notably at the value of 2.0.It was, in addition, clarified that the castability decreased in increasing the weight ratio of(M_ingot/M_coil).

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As has been previously reported, the effective factors upon corrosive dissolution of casted tin were measured. Two factors, the kinds of solution and the immersion time, were significant.The kinds of solution played the most decisive factor: the most dissolution was revealed in the case of 1% lactic acid solution-the amount of dissolution after three months was approximately 10 mg/cm² (about 850 times that of silver). The periodic effect was observed only in 1% Lactic acid solution and the dissolution increased in proportion to the passage of time.

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Solvent weldability of polysulfone(PSF)was studied as a series of investigation on the welding of dental PSF for mending and adjusting. Welded joint efficiency of PSF welded by only solvents such as chloroform, was about 30%, whereas the efficiency rised up to 50% using the chloroform solution containing 23% PSF by weight. The strength of the welded PSF increased with decreasing scarf angle of the weld. Fracture of the welded PSF having scarf angle of 30°did not take place at the weld, but took place at the base PSF. Necking occurred in the course of stretching process of the base PSF, and elongation of the PSF became about 2 times. On the other hand, elongation of the welded PSF became about 6-10%, and elastic modulus of the welded PSF differed from that of the base PSF. It was observed that fracture surfaces of the base PSF are smoother than that of the welded PSF.

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No effective method of the determination of the edge strength has yet to be found. The purpose of the present investigation was to determine the marginal fracture toughness of several types of composite resins by means of the rattler tester. The rattler test as one of the MPIF standard tests is frequently employed to assess the edge stability of the green compact in powder metallurgy. Five cubic specimens (6×6×3 mm)of each material were prepared and kept in a desiccator until they showed a constant weight. Five specimens were put in the cylindrical screen cage, 9 cm in diameter, made of bronze net(14 mesh)and the cage was revolved 10,000 times at 87rpm.The rate of the weight loss of each material was calculated by weighing every 1,000 times.The rate is represented as the marginal fracture toughness in accordance with the edge brittleness of restorative materials. The results of ratter test showed significantly higher fracture toughness for microfilled composites than the regular composites. With MFR, the increase of the weight loss stopped after 5,000 or 6,000 times revolution, whereas the weight loss of the regular composites continued to increase in proportion to the number of revolution.These results in combination with the SEM studies suggest that the bonding at the filler-matrix interface of the regular composite is more unstable than that of the MFR.

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Viscoelastic properties of two acrylic denture base resins(heat-curing resin and fluid resin), a polycarbonate denture base resin and a polysulfone denture base resin have been studied by using dynamic viscoelastometer (Rheovibron DDV-II). Also, the glass transition temperature (Tg) of these resins have been examined by dilatometry method. The decreasing rate ((dE′)/(dT)) of storage modulus (E′) with increase in temperature was more rapid for acrylic resins than for polycarbonate and polysulfone resin. Furthermore, E′of acrylic resin was strongly affected by test conditions, especially frequency for measurement. The glass transition temperatures determined from variation of specific volume with temperature of each material were 110℃ for heat-curing resin, 90℃ for fluid resin, 150℃ for polycarbonate resin and 190℃ for polysulfone resin. From these results, it can be seen that polycarbonate and polysulfone resins show fairly toughness compared with acrylic resins.

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The measurement of spectral irradiance for various dental visible-light sources revealed that maximum spectral irradiance of TRANSLUX, PRISMA-LIGHT and HELIOMAT was 5400, 3200, and 2800 (μW・cm^-2・nm^-1), at 500 nm respectively, and that the maximum intensity for ELIPER was obtained at 450 nm, which was 3600 (μW・cm^-2・nm^-1). All the visible-light cured composite resins examined in this investigation were found to contain BIS-GMA as a monomer component and the filler contents of these resins were from 73 to 79 wt%.
The heat of polymerization per mole determined by differential scanning carorymetry was largest for PRISMA-FIL, smallest for COMMAND and the value for DURAFILL was comparable to HELIOSIT. The depth of cure for five visible-light cured composite resins by visible-light irradiation for 20 sec at the distance of 3 mm from the resins was in the order of PRISMA-FIL, DURAFILL, HELIOSIT and VISIO-DISPERS. The depth of cure increased with the exposure time of visible-light, and was also affected by the shades of resins. It was observed by the measurement of working time of resins with 15000 lx dental light for illumination that PRISMA-FIL was most sensitive to the light, the working time of which was about 100 sec.

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For the purpose of developing new plastic filling materials instead of amalgams, various properties of gallium alloys based on 80%Sn-20%Cu which was added platinum, palladium and silver were investigated, and following conclusions were obtained.
1)Dimensional change of all gallium alloys satisfied ADAS No.1(±20μm/cm).The dimensional change was tended to decrease with the addition of platinum, palladium below 5 wt% and silver below 20 wt%.
2)Compressive strength at two days after mixing and dimensional change correlated inversely to each other. Compressive strength of all specimens at seven days after mixing was more than 20 kgf/mm². It was increased with the increase of palladium and decrease of silver.
3)Shirinkage rates of specimen-length when compressive strength measured which were correlated inversely with compressive strength were 2.9-4.2% and 0.9-3.3% at two and seven days after mixing, respectively.
4)Specimens which could endure the weight of the flow test (JIS) didn't include palladium.
5)Vickers hardness of specimens at seven days after mixing were 117-161. For the effects of added metals, it was clearly decreased, when platinum was added more than 25 wt%.
6)Loss in weight of all specimens by the corrosion in 1% Lactic acid solution ranged from 1.4 to 2.5mg/cm².
7)All specimens have passed the discoloration test of JIS-T 6108(for dental silver casting alloys).

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About representative compositions of gallium alloys as the plastic filling materials (based on 80 wt%Sn-20 wt%Cu)which reported in part 1, change of Vickers hardness and compressive strength of various periods from mixing were investigated and X-ray diffraction analysis, their changes with time and area analysis by EPMA were made.
1)Vickers hardness and compressive strength of all specimens increased with time, their pattern of increase were different from each to each.And there were direct correlations between Vickers hardness and compressive strength.
2)The following results were obtained by area analysis.Almost all amount of Platinum and Palladium concentrated in particles.Gallium penetrated into particles, but its degree of penetration was limited by the addition of Palladium.
3)From the results of X-ray diffraction analysis, PtSn, Sn, CuGa₂ and Ag_0.72Ga_0.28 were found. Moreover, it was found that diffraction strength of Sn, CuGa₂ and Ag_0.72 Ga_0.28 increased with time.
4)Most suitable composition concluded in this study was 48 wt%Sn-12 wt%Cu-25 wt%Pt-15 wt%Ag.

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Changes in the powdery composition of phosphate-bonded investment, Ceramigold, on exposure to 100% relative humidity atmosphere were investigated by means of X-ray diffraction and differential thermal analysis(DTA).
As the exposure was prolonged, setting agents(NH₄H₂PO₄ and MgO)reacted owing to moisture. The quantities of these compounds changed as follows. The quantity of NH₄H₂PO₄ decreased, became below half after 2 days of exposure. NH₄H₂PO₄ was not detected after 6 days of exposure. Mg(NH₄)₂H₂(PO₄)₂・4H₂O and MgNH₄PO₄・6H₂O were detected after 1 day of exposure.The quantity of the former increased from 1 to 6 days of exposure, but unchanged from 6 to 10 days of exposure, and decreased from 10 to 27 days of exposure. Mg(NH₄)₂H₂(PO₄)₂・4H₂O was not detected after 27 days of exposure. The quantity of the latter increased except both from 2 to 4 days of exposure and from 6 to 10 days of exposure when that unchanged. Changes in powdery composition of setting agents owing to moisture is similar to the reaction of setting agents during setting.

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