In the previous report, we examined the change of the physical properties of LTV vinyl silicone rubber (Toray Silicone, CF5005) due to 3-month-long storage in water, and that of adhesive strength with methacrylate resin due to 2-month-long strorage in water, and obtained stable results in both cases.
But, to determine whether it is suitable for use as a resilient denture relining material, a longer test period is necessary. Therefore in the present studies, the specimens were stored in 37℃ water for 5 years (1979〜1983), the physical properties and adhesive strength with methacrylate resin were examined. The results are as follows:
1) No decrease in hardness, tensile strength, elongation and tear strength was observed.
2) Water absorption was extremely small, and there was no discoloration.
3) Decrease in adhesive strength with methacrylate resin was not noted.
4) From these results, it is appears that the present material shown excellent stability, even if it is used in the oral cavity for a long period.

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To clarify the staining of porcelain with the alloys used for porcelain fusing in the fabrication of the ceramometal restoration, 21 kinds of Au-Pd-Ag system alloys and those containing 5 wt% Sn or In were made. The effects of porcelain staining and the physical mechanical properties of these experimental alloys were investigated and the following results were obtained.
1) The color difference ΔE^*ab (in NBS unit) were significantly affected by the Ag content, but were not by the Au and Pd content. The ΔE^*ab gradually increased with the increase of the Ag content and the color of stained porcelain shifted to yellowish.
2) It was suggested that the yellow shift of the boundary layer of porcelain in Ag containing alloys was not attributed to silver oxide, but to colloidal metalic silver.
3) Porcelain staining decreased in following order: the alloys without additives, those containing In and those containing Sn.
4) A correlation was found between hardness (Hv) and tensile strength in the alloys without additives. The alloys containing In or Sn were about twice as hard as the alloys without additives.
5) The thermal expansion coefficients were affected by Ag and Pd, and increased with the increase of the Ag content, but decreased with the increase of the Pd content. Although the Sn or In containing alloys showed similar pattern, the range of composition (13 to 17×10^-6/℃) became smaller. The total averaged value of the thermal expansion coefficient was 15.5×10^-6/℃ for the alloys without additives, and 15.7×10^-6/℃ for Sn or In containing alloys. The coefficient of the alloys containing additives was slightly greater than those without additives.

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4-(3-Methacryloyloxypropoxycarbonyl)phthalic anhydride (MPRPA), 4-(4-Methacryloyloxybutoxycarbonyl)phthalic anhydride (MBPA), 4-(2-Methacryloyloxyethoxycarbonyl)phthalic anhydride (4-META) and 2-Benzoyloxyethyl methacrylate (BEMA) were synthesised and MMA-TBB type adhesives containing these monomers were prepared. Adhesive strength of these adhesives to the 5 kinds of dental alloys polished by emery paper was measured after a 2, 000-time thermal cycle test. Adhesive with MBPA showed the best adhesion to the alloys of all adhesives.
Adhesive strength was provided by cohesive failure area of the fracture surface in case of adhesion of alloys by MMA-TBB type resins. A 50 μm-thickness of adhesive showed better adhesive strength than that of 150 μm, and adhesive strength was increased by heating the adhered samples for 1 hour at 60℃.

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To investigate the casting shrinkage of higher-melting dental alloys, the densities of pure nickel, the system of Ni-Cr and Ni-Cr-M (M: Si, Cu, Mo and Mn), and commercial dental casting Ni-Cr alloys were measured at temperatures ranging from room temperature to about 1, 700℃ by using an apparatus which was based on the sessile drop method. Thermal and solidifying shrinkage of dental Ni-Cr alloys were calculated from these density changes.
The voluminal shrinkage during solidification of pure nickel was 4.91 vol% and that of Ni-Cr alloys in the range of 3.96 to 5.79 vol%, which were independent of the chromium contents. The shrinkage of Ni-Cr-M alloys were from 2.70 to 5.46 vol%, and that of the Ni-Cr-Si alloys decreased with the increasing amount of silicon. The shrinkage of commercial dental casting Ni-Cr alloys were from 2.59 to 4.69 vol%.The vacancies in the cast caused by the crystal growth during solidification have direct effects upon the solidifying shrinkage. Thus the growth of dendritic structure causes many microporosities in the cast and it results in the small shrinkage. The linear shrinkage of dental Ni-Cr alloys from solidus temperature to room temperature were from 2.07 to 2.78%, which were clearly larger than those of dental gold alloys.

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The effets of Cr contents on the corrosion resistance of Ni-Cr binary alloys and Mn, Si, Cu or Mo contents of Ni-Cr binary alloys were investigated. The alloys were prepared with the composition of Cr ranging from 0 to 39.8 wt%. Additions were made to Ni-5% Cr and Ni-20% Cr alloys as follows:Mn 0.5, 2.0 wt%, Si 2.0, 5.0, 10.0 wt%, Cu 2.0, 5.0, 10.0 wt%, Mo 2.0, 5.0, 10.0 wt%. The corrosion resistance was assessed by the release of Ni in Ringer's solution at 37℃ and 1% lactic acid at 37℃, and by electrochemical corrosion behavior in Ringer's solution.
The results are summarized as follows.
Ni-Cr binary alloys were classified into three types of Cr ranging from 0 to 5.5 wt%, Cr from 10.8 to 21.0 wt% and Cr from 26.3 to 39.8 wt% according to the release of Ni in Ringer's solution. It is necessary to keep the Cr contents to a minimum of 10.8 wt% for released Ni and rest potential values in Ringer's solution and 15.7 wt% for restraint of released Ni in 1% lactic acid. Alloys containing Mn exhibited the decline in the corrosion resistance. Si addition to Ni-5% Cr alloy had the effect of increasing the corrosion resistance and the alloy with Si 4.6 wt% showed the best corrosion resistance. Alloys containing Cu exhibited good corrosion resistance to the release of Ni and the rest potential value, but not in the anodic polalization curve. Alloys containing Mo exhibited good corrosion resistance and the optimum additive amount of Mo was affected by Cr content. In the case of the alloys with Cr 5.5 and 21.0 wt% contents, the optimum additive amounts of Mo were 1.7 and 7.1 wt%, respectively.

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Enamel prisms may be fractured by the instrument following careless application of bonding agent to acid-etched enamel. In such a case, the adhesive strength between tooth and restored resin is considerably reduced, causing impaired marginal adaptation. In this investigation, the effect of added load during the application of bonding agent on the resultant adhesive strength was examined quantitatively. The effect of added load was so apparent that, for example, an adhesive strength of approximately 190 kg/cm² was obtained following the loading of 0.01〜0.03 g, when a piece of sponge was used as the insutrument for application. However, it decreased to either 100 or 50 kg/cm² when a load of 2〜3 or 7〜10 g was applied. These findings suggest that application of bonding agent should be made as carefully as possible to avoid the damaging of acid-etched enamel prism following its application.

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This study was to investigate the influence of aluminum content on the properties of sintered Ti-Al alloy. The alloys were added from 2.5 wt% to 15.0 wt% aluminum powder to titanium powder. The effect of added aluminum powder on the properties of sintered compacts was investigate by measurement of thermal expansion curves, density of green and sintered state, compressive yield strength and sintered shrinkage.
Experimental results were as follows.
1. Ti-Al green compacts exhibited abnormal expansion at approximately the melting point of aluminum. Maximum expansion of these compacts increased remarkably with aluminum content. Final sintered shrinkage decreased substantially as the aluminum content increased. When -250mesh Ti powder was used, the expansion ocurred in the case of over 7.5 wt% aluminum powder contents,
2. The compressive yield strength of Ti-Al sintered compacts was maximum at 7.5 wt% aluminum powder content.
The findings show that the fitness of sintered titanium alloy prosthetics can be improved.

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The mechanism of setting expansion of phosphate-bonded investment was studied by SEM and X-ray diffraction analysis. Six kinds of investments were prepared by mixing commercial glass beads (as a base), magnesia clinker and NH₄H₂PO₄ (as binders). The content of glass beads in the investment powders was kept constant at 80%. The ratio of magnesia clinker to NH₄H₂PO₄ varied from 12/8 to 4/16. Three kinds of 20% colloidal silica solution were mixed with the investment powders at the L/P ratio of 0.24. The findings were as follows.
(1) The time on setting expansion decreased with increasing ratio of magnesia clinker to NH₄H₂PO₄.
(2) The setting expansion after 2 hr showed the maximum at the ratio of magnesia clinker to NH₄H₂PO₄ of 7/13 or 6/14. However, the X-ray diffraction data of MgNH₄PO₄・6H₂O did not agree with this result.
(3) In spite of the same concentration of colloidal silica solution, the values of setting expansion of mixtures differ from each other. The solution at maximum setting expansion had uniform sized and spherical silica particles, and had high ability to hold water.
(4) As an initial product of setting reaction, large needle-like crystals (probably Mg(NH₄)₂H₂(PO₄)₂・4H₂O) were found. The shape of final product MgNH₄PO₄・6H₂O was plate or block.

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The relationship between the polymerization and the monomer structure of various dimethacrylates was investigated utilizing differential scanning calorimetry. Five ethyleneglycol dimethacrylates, three alkyleneglycol dimethacrylates, urethane dimethacrylate (UDMA) and 2, 2-bis[4(3-methacryloxy-2-hydroxypropoxy)phenyl]propane (Bis-GMA) was used. The polymerizations were isothermally conducted in sealed aluminum pans at the temperatures of 70℃, 80℃, 90℃, 100℃ and 110℃.
The thermogram of the dimethacrylates in isothermal bulk polymerization exhibited several exothermic peaks and the rate and extent of polymerization obtained from the thermogram increased with the increase of the polymerization temperature. The rate and extent of polymerization of the ethyleneglycol dimethacrylates were obviously dependent on the monomer structure, that is, the rate of polymerization increased with the decrease of the chain length between both two functional groups and the extent of polymerization increased with the increase of the chain length, while, no obvious dependence on the monomer structure was observed in the alkyleneglycol dimethacrylates under the conditions used. UDMA showed the highest rate of polymerization at all temperatures examined, and nonaethyleneglycol dimethacrylate showed the highest extent of polymerization of all the dimethacrylates. Both the rate and extent of polymerization of Bis-GMA were the lowest among the dimethacrylates.

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Migration of crystal grains in liquid alloy during solidification by dental-centrifugal and gaspressure casting processes was investigated.
Distribution of crystal grains in cast structure and solidification time were measured, and moving velocity of crystal grain in liquid alloy was calculated.
The results confirmed that solidification of alloy by dental-centrifugal casting process is dependent on the migration and accumulation of crystal grains in the liquid alloy caused by centrifugal force, that distribution of crystal grains in cast structure is strongly dependent on the rotational speed of the arm of cast machine for one second from the beginning of cast. Solidification of alloy in cast using full crown-like molds is also identical. In gas-pressure casting process, migration of crystal in the liquid alloy caused by gravity does not occurred.

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To study the wettability of porcelain to porcelain-fused-to-metal (PFM) alloys, an apparatus equipped with a CCD camera and a personal computer was made for measurements of the contact angle. In experiment I, the performance of the apparatus was tested using an opaque porcelain and PFM alloys on the market. Compared to the usual photographic method for measurements, no significant differences in the values of the contact angle were observed. In experiment II, the contact angles and works of adhesion between the porcelain and ten experimental PFM alloys which were prepared by adding 0, 2, 4 and 6 wt% Ti, Sn, or Mo to an 80 wt% Ni-20 wt% Cr master alloy were determined using the appartus that had been improved based on experiment I. As a result, the work of adhesion (x) correlated highly significantly with the corresponding previously reported pull-through shear bond strength (y), and the regression line was y (kgf/cm²)=-21.4+0.4136x (erg/cm²).

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Yield strength of dental casting silver alloys was obtained from a compressive test, and the influence of size of small casting specimens and testing conditions upon yield strength and compressive strength was investigated.
Four factors (diameter of specimen, L/D ratio of specimen, testing speed, lubricant) were analyzed by variation analysis using the orthogonal table L₉.
Yield strength and compressive strength of all alloys were significantly affected by diameter of specimen and specimens of 2.0 mm in diameter had higher strength.
According to this study small specimen (2.0 mm in diameter, 3.0〜4.0 mm in length) was found to be useful to evaluate strength of dental silver alloys economically.

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In this study mechanical strength of eight kinds of silver alloys were investigated by the compressive yield strength and Vickers hardness to compare with the strentgh of ADA type gold alloys. (Au)-Ag-Pd alloys were found to have satisfactory mechanical properties as alternative alloys, but Ag-Sn-Zn alloys and Ag-In alloys were found to have poor yield strength or poor plasticity.
A correlation was observed between Vickers hardness and compressive yield strength in tested silver alloys.

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A method to measure the dimensional changes directly with restraining the deformation induced by measuring load of elastic impression materials was devised. A small magnet was attached to a thin steel net burried in the upper surface of the specimen to touch the terminal of the lever-type gauge head of an electronic comparator turned upside down.
An alginate and condensation silicone impression materials were used in this study. The former was measured for 60 minutes and the latter was for 24 hours respectively from 5 and 8 minutes after the start of mixing with the change in air, in 100% relative humidity and in water.
The results of experiment indicated that the time-sequence changes from immediately after the hardening were easily and accurately measured in every environment by this method. An environmental influence was found on the alginate, however, it was not found on the silicone.

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There are not a significant different between adhesive strength and compressive strength in case of whole dental cements, but resinous adhesives showed significant correlations. The various properties of resinous adhesives decreases with higher temperature, for with low softening temperature.
The compressive strength of resinous adhesives at the 37℃ and 60℃ were about 46% and 18% of the value at 23℃, while the adhesive strength at same conditions were about 95% and 65%. But, in case of composite resinous adhesive, the respective values were 85% and 78% in compressive strength, and 84% and 76% in adhesive strength.
However, even at the higher temperature, the absolute adhesive values of resinous adhesives are much higher than that of the conventional dental cements.
These cements were use in the mouth, which has higher temperature than the room temperature at which the test with many properties are generally done. Therefore, the measuring of adhesive strength should be done at a moderately high temperature for the above reasons.
This phenomenon may be one of the reasons concerning the decrease in adhesive strength over a long period.

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By using the technique previously reported, different type alloys were joined by simultaneous casting into a single mold separated by a platinum foil. The image of structures around the joined area of 20K gold alloy, platinum gold alloy and Au-Ag-Pd alloy were observed.
In this study, the joined areas of KIK, Au-Ag-Pd alloy and Ni-Cr alloy were observed under LM and SEM and analysed by EPMA.
KIK was fused to the platinum foil without segregation like the 20K gold alloy or platinum gold alloy as observed in a previous study. Au was diffused into platinum foil with the diffused depth of 1 μm. In the case of Au-Ag-Pd alloy, the segregation was observed under LM and SEM. The diffused element into the platinum foil was Cu with the diffused depth of about 6 μm. In the case of Ni-Cr alloy, the diffused layer was also observed. The diffused elements into the platinum foil were Mn, Ni and Cu with the maximum depth of about 18 μm.
Platinum was also diffused into these alloys with the maximum depth of about 100 μm.

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A new type molecular composites, copolymers of methyl methacrylate and rigid siloxane oligomers, which have a ladder-like structure, have been developed for resins for dental use, for example, hard crown and bridge, composite and denture base resins. The oligomers made from a variety ratio of γ-methacryloxypropyl trimethoxysilane and phenyl triethoxysilane were lucid and viscous liquids, with molecular weight of about 1100. The viscosity of the oligomers increased with the number of phenyl substitutes, and were lower than that of Bis-GMA.
Compressive strength of the various MMA-copolymer, which contained 20 wt% of the oligomers, were higher than that of the copolymers with same weight of polyfunctional monomers, such as 3G and Bis-GMA.
Based on considerations of the degree of crosslink in the various copolymers and structure of siloxane bond, it is assumed that the copolymer is reinforced not only by crosslinkage involved with the polyfunctional substances, but by the contribution of rigid structure of the siloxane oligomers.

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A new casting machine for NiTi alloys was developed, and mechanical properties and fitness of casted NiTi alloys were studied. Good mechanical properties and finess were obtained by using graphite coating on phosphate bonded investment.
The castings of pure titanium, Ni-Cr and Co-Cr alloy were also examined by using this casting machine. Reaction between metals and phosphate bonded investments was markedly decreased by heated mold in vacuum, and the elongation of casted titanium and Co-Cr alloy were greatly increased.
The casting machine developed in this study may be very useful not only for casting of NiTi alloys but also for those of titanium and other base metal alloys.

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Pressure exerted to resin during trial closure and polymerization was measured with a strain gage transducer. Further, internal stress of heat-curing resin during polymerization in the flask was investigated.
When load of 1, 750 kgf was employed at trial closure, the highest value of the pressure to resin was about 40 kgf/cm². Though the pressure to resins during polymerization in water bath at 70℃ and in boiling water went up to 10 kgf/cm² and 17 kgf/cm², respectively, the pressures to resins were 0 kgf/cm² before the exothermic heat was evolved.
The internal stress of the resin during polymerization in water bath at 70℃ for 240 min. and at 70℃ for 60 min. and then in boiling water for 30 min. increased with an increase in polymerization time, and was 300 kgf/cm² and 350 kgf/cm², respectively, after the termination of polymerization. On the other hand, the internal stress of the resin during polymerization in boiling water for 40 min. decreased from 60 kgf/cm² to 0 kgf/cm² when the temperature of the resin was about 120℃ after 20 min, and was 250 kgf/cm² after the termination of polymerization.

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