An adhesive monomer (β-methacryloyloxyethyl hydrogen succinate) was electrodeposited on a dental alloy surface to investigate improvement of the adhesion to dental methacrylate resin. In this experiment, bond strength was examined in relation to the treatment condition (solution concentration and current) for electrodeposition on 18-carat gold alloy. In addition, findings were compared with the previous results for 12% Au-Ag-Pd alloy, Co-Cr alloy and pure titanium. Results:A functional monomer was electrodeposited on the alloy surface and its carboxylate ion formed an ionic bond, but its methacryloyl group did not react. Effective electrodeposition conditions for improving the bond strength between 18-carat gold alloy and methacrylate resin were a concentration of 20-30% and treatment current of 0.5-1 mA. Bond strength under these conditions was 11.5-13.3 MPa. This value represented the highest bond strength among 4 kinds of dental alloys.

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This study is investigated the possibility of removing investments after casting or oxidation films produced on the cast alloy using a compact water-jet device. This device has a nozzle of 0.17 mm in diameter and can inject high-pressure water (50-2,000 kgf/cm²) during the mobile sample stage at a rate of 0-25 mm/min. High-pressure water was injected to two investments and four cast alloys after casting to remove investments and oxidation films, and then the width and depth of the flutes were measured. The flute of investments was deeply cut by enlarging the water pressure rather than the stage speed. When the sample stage moves at 8.7 mm/min, a water pressure of 700 kgf/cm² is suitable for the removal of oxidation films on the cast alloy. As a result, it was found that water jet device could be used for the removal of investments and oxidation films on cast alloy.

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This thesis investigated pure titanium casting using sintering molds to improve the reactive layer created by phosphate-bonded investment. It was observed that sintering began above l,100℃ temperature. The color of pure titanium crowns appeared close to the metallic color itself, as the burnout temperature increased. On element analysis of the surface layer, the more the burn out temperature increased, the more the depth of the reactive layer decreased. By observing under an electron microscope, a wheat gluten-like component was noted when the temperature rose above l,100℃. Al₂TiO₅ concerned with the sintering of molds. Therefore, it was suggested that the reactive layer is improved by sintering molds even when using a phosphate-bonded investment with a main component of SiO₂.

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To realize aesthetic othodontic wires, we have been developing the FRP wires in combination with biocompatible CaO-P₂O₅-SiO₂-Al₂O₃ (CPSA) glass fibers and PMMA matrix by a hot drawing method. These wires are mainly intended to be used for the movement of teeth during the initial stage of treatment. In this study, a photo cure polymerization method was applied to form the rectangular timber with a sufficient torque force for rotation of the teeth. The FRP wire composed of CPSA glass fibers and UDMA matrix showed a sufficient flexural strength. For torsional properties, however, the wire had a much smaller torque compared with that of Co-Cr and Ni-Ti wires. The FRP using dental composite resin for matrix showed a load 4 times of UDMA based FRP wires. The torsional load was increased to 1/2 of Ni-Ti wire. It was found that the fiber content mainly contributes to flexural load while the use of stiff materials such as composite resin for the matrix is much more effective for improving torsional properties.

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Full veneer cast crowns were made from stone dies obtained from vinyl polysiloxane impressions using custom trays. The marginal discrepancies between the crowns and the stone dies or original metal die were measured. The inside discrepancies between the crowns and the original die were also obtained by measuring the thickness of silicone fit checking material. Although the crowns adjusted to the stone dies revealed small marginal discrepancies on the stone dies as compared to the crowns as cast, both crowns had the same marginal adaptation and thickness of the fit checking material on the original die. The vent holes on the tops of the crowns for the fit checking material revealed the almost same axial discrepancies as compared to the cement thickness reported in the other studies. Both measurements of marginal and inside discrepancies detailed the fit of cast crowns.

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To evaluate the biocompatibility of refractory metals in group IVa and Va, these metals were implanted in rats, then subjected to metal surface roughness test by atomic force microscopy, histological examination by optical microscopy, histomorphometry by image analyzer, mapping of metal dissolution by X-ray scanning analytical microscopy and EPMA, observation of osteogenesis by confocal laser scanning microscopy (CLSM) and highly sensitive analysis by ICP. None of metals except vanadium showed any inflammatory response. The amount of new bone changed little and the bone-metal contact increased markedly from the 2nd to 4th week after implantation. The image of fluorescent labeling by CLSM and calcium enrichment by EPMA revealed that remodeling and calcification proceeded. While vanadium showed a suppressive effect in bone formation. ICP showed vanadium dissolved after immersion in simulated body fluid. These results suggest that zirconium, hafnium, niobium and tantalum have good biocompatibility equivalent to that of titanium.

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Eleven types of Ti-Ni alloy or thodontic rectangular archwires, four kinds and three sizes, were quantitatively investigated for torsional properties by a torsional test, in relation to the thermal change associated with the phase transformation by differential scanning calorimetry. Three kinds of the wires showed hysteresis curves characteristic of super-elasticity in the torsional moment-angle diagrams, while the torsional moment changed relatively linearly with the angle in the case of the other wire. The wires showing low values for transitional angle, transitional moment and moment-angle rate, which were quantitative parameters for the super-elasticity in torsional properties, exhibited sharp peaks during the thermal change accompanying the phase transformation. This appeared to influence the torsional properties in addition to the transformation temperatures. The wires showing no super-elasticity exhibited low peaks, and the transformation temperatures were considerably higher. There was no clear difference in the residual angle of the wires.

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Deformations of crowns on model teeth were measured with strain gages for the cases of experimental crowns which had uniform thickness at their axial surfaces, and the effect of axial metal thickness on the rigidity of the crown and the cement fracture strength was examined. Cemented crowns exhibited smaller strains than those not cemented, showing that cementing integrated the crown structures with the abutment teeth. Among the structures of cemented crowns and abutment teeth, that of the axial metal thickness of 0.3 mm had cement failure at the smallest loads. As the metal thickness was increased, the crown deformation decreased and cement failure loads increased. For a thickness greater than 0.7 mm, however, the increase in failure loads was not obvious. Accordingly, the rigidity of dental prostheses should be one of the most important design factors in preventing failure under occlusal load, and it is recommended that the axial surface of prostheses should have a thickness of at least 0.7 mm.

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