[in Japanese]

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　We developed a process for making implant materials. Composite implant materials were produced by double coating to titanium plate with two kind of mixed powder. One was a mixture of titanium oxide and aluminum oxide powder and the other a mixture of aluminum oxide and hydroxy apatite powder. These coating were applied by a plasma flame spray process.
　Titanium plates were preheated at 500℃, 600℃, 700℃, 800℃ for oxidation of their surface. The properties of these implant materials were examined with respect to bending strength, young's modulus, XMA, X-ray diffraction analysis.
　The maximum bending stength, proof strength and young's modulus were obtained with composite implant material which titanium plate was preheated at 500℃ and then double coated with a mixture of 13% titanium oxide and 80% hydroxy apatite to aluminum oxide powder.
　The coating layers were found to chemically combined at the interface. Negligible decomposition of hydroxy apatite by plasma flame spray was observed by the X-ray diffraction pattern.

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　In this study 1) the change of the permeabillity rate, 2) effect of powder liquid ratio and 3) change of pH of free phosphoric acid of zinc phosphate cement that permeated through dentinal tubles of cattle's teeth and glass fiber filter sample were investigated.
　The free phosphoric acid continued to permeate the dentin even though its initial setting was completed. The peak of the permeability was at 9 hours after the initial setting.
　Three different liquid powder ratios of the cement (powder/liquid=1.25 g/0.5 ml, 1.45 g/0.5 ml and 1.65 g/0.5 ml) did not affect the rate of permeability of the free phosphoric acid.
　After the tooth sample cavity was filled with cement, four major elements that permeated the dentinal tubules were detected in the following concentrations: 4.61 ppm P, 3.41 ppm Ca, 1.44 ppm Mg and 0.08 ppm Zn. This indicates that the tooth structure was decalcified by the etching effect of the free phosphoric acid and simultaneously the phosphoric acid itself, especially the pH was reduced.
　In the control sample in which the cavity was filled with distilled water, the concentrations of the four major elements were lower (2.26 ppm P, 2.39 ppm, Ca, 1.44 ppm Mg and 0.08 ppm Zn).
　In the glass fiber filter sample, which was not affected by the phosphoric acid, the elements composing the cement (P, Zn and Mg) mainly permeated through the dentin (20.48 ppm P, 10.04 ppm Zn, 3.42 ppm Mg and 0.40 ppm Ca).
　In the glass fiber filter control sample in which the cavity was filled with distilled water, the concentrations of the four elements were significantly low (0.16 ppm P, 0.037 ppm Ca, 0.098 ppm Mg and 0.12 ppm Zn).

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Residual stress in injection molded specimens having a round or rectangular hole was investigated by photoelastic analysis. Though molten resin flowed as the resin surrounded either side of the hole, and met at the opposite side of the gate, one of principal stress trajectories derived from isoclinic patterns coincided roughly with the shapes of the flowing resin front. Stress in the specimens was concentrated about the hole, and the greatest concentration developed at the side of the hole near the gate. The isochromatic fringe order curves about the round hole were smoother than those about the rectangular hole, and the stress concentration in the specimens having the round hole was less that in the specimens having a rectangular hole. In specimens having rectangular holes of the same size and the same shape, the molten resin readily flowed around the rectangular hole with it's short side pointing to the gate in comparison with that with it's long side pointing to the gate. Though both specimens had a maximum principal stress of 207.0 kgf/cm², the extent of this stress was small in the specimen having the rectangular hole with it's short side pointing to the gate.

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　Pressures produced during compression of impression materials between parallel disks were measured with diaphragm pressure transducers and analyzed hydrodynamically to clarify the relationships between the impression pressures exerted on tissues and factors affecting them in impression procedures.
　The amount of pressures ranged according to the viscosity of materials, tray seating speed, and the thickness of materials, which was the most effective when the tray seating speed was constant. The force applied to the tray seems to be important in regulating the impression pressures because it is the integrated value of the pressure distribution.
　On the other hand, the form of pressure distribution depended on the tray designs. It was flat in a relieved area but the effect to reduce pressures was limited by the depth that the tray was relieved, while pressures beneath an escape hole were extremely reduced when the diameter of the hole was more than about 2 mm.
　The pressure distributions obtained from theoretical analyses were larger than those of the experiments in absolute values but well reflected their tendencies. Thus, this method of analyses and the basic theories are thought to be useful guides when the impression pressures are controlled clinically.

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　An apparatus was constructed for measuring adhesive strength under compression shear stress, and adhesion tests were done on the basis of the measured strength of adhesion between dental adhesives and SUS 304. Two dental adhesives, Superbond C&B (SB C&B) and PANAVIA EX (PEX), were examined. The Ni-Cr-Co-Mo quarternary alloy, which was chosen as a potential material for an adhesion bridge, was fused and cast to obtain samples, and their mechanical properties and resistance to tarnishing were determined. Alloy samples with good properties were selected and their respective adhesive strengths to SB C&B were measured under compression shear stress. The adhesive strength of SB C&B to SUS 304 varied with aging temperature, and was about 550 kgf/cm² when the samples were left to stand at 60℃. For the samples aged at 20℃ and 37℃, adhesive strength further increased when they were subjected to 30 thermal cycles of 120 s in the water adjusted to 4℃ and 60℃, respectively, whereas it decreased in samples aged at 60℃. When applied to SUS 304, the adhesive strength of PEX was less affected by aging temperature than SB C&B, though the measured values themselves were smaller with a larger coefficient of variation.
　Tests were made on 24 samples of the Ni-Cr-Co-Mo alloy with a molybdenum content fixed at 15 wt%, cobalt and chromium contents ranging from 5 to 30 wt% and from 10 to 25 wt% respectively, and a nickel content accounting for the rest. The results suggested that an alloy with a composition in the range of 45±10Ni-20±2Cr-20±8Co-15Mo (wt%) has excellent mechanical properties and resistance to tarnishing. Being capable of bonding strongly to SB C&B, Alloys 15, 16 and 17, which stay in the above range, were found to have excellent potential as practical materials for an adhesion bridge.

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　The properties of Co alloys (Co-Cr, Co-Ni, Co-Pd) for porcelain fusing were studied. Tensile strength, elongation, micro-Vickers hardness and thermal expansion were measured, and bonding strength between Co alloys and porcelain was studied.
　Tensile strengths of Co-Cr, Co-Ni and Co-Pd alloys were 164〜499 MPa, elongations 0.8〜18.7%, Vickers hardness numbers 91〜382. These values were similar to those of nonprecious alloys for porcelain fusing. Thermal expansions of Co-Cr, Co-Ni and Co-Pd alloys were the same as or slightly larger than those of porcelain fused alloys on the market. The maximum bonding strength was obtained with 70% Co-30% Pd alloy.

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　Dental base metal alloys were polished by an ultrasonic polisher at a frequency of 28.5 kHz and polishing efficiency and surface texture were examined.
　The amount of grinding of Co-Cr, Ni-Cr and pure Ti by the sintered diamond grinding wheel increased as the grinding load increased from 100 to 500 g.
　After casting specimens of Co-Cr and Ni-Cr were cleaned by sandbasting, specimens were coarse polished by diamond grinding wheels, aluminum oxide grinding wheels and lapping powder of aluminum oxide. The diamond wheel was found to be most efficient. Finishing could be made by lapping using diamond paste, but it was difficult to obtain a mirrorlike finished surface even with 3 μm paste.

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　Three kinds of dental alloys (Co-Cr, Ni-Cr, Ag-In) were ground by newly developed TiC-containing wheels with electric conduction. Both the mechanical grinding and the electro-mechanical grinding with several rotational speeds and grinding loads were performed. Also factors affecting the amount of grinding of tested alloys were analyzed and the grinding surface was also observed.
　The amount of grinding of all alloys were significantly affected by the grinding method, the rotational speed, and the grinding load. The electro-mechanical grinding showed higher amount of grinding than the mechanical grinding. The amount of grinding by the electro-mechanical grinding increased as the rotational speed increased from 250 m/min to 750 m/min but decreased after the rotational speed rose to 1000 m/min.
　The highest amount of grinding was obtained by the electro-mechanical grinding with the grinding load of 150 g, the rotational speed of 750 m/min and the grinding wheel No. 4; a better surface texture was also observed under these conditions.
　The electro-mechanical grinding was found to be useful to shorten the grinding-polishing system of dental alloys.

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　The fracture mechanism of the castings made from Ag-binary-alloys (Ag-Pd and Ag-Cu) was investigated by tensile tests, microfractography, microstructure observation and X-ray microanalyses.
　I-type dimples were formed by grain boundary brittle fracture and its propagation. They occupied the greater part of the fracture surface of single phase alloy that showed high ductility.
　II-type dimples were observed very numerously on the fracture surface of binary phase alloy that showed high mechanical strength and small elongation, and somewhat numerously on the single phase alloys that showed higher mechanical strength than the others. II-type dimples seemed to be formed by the accumulation of dislocations, and their number was related to the mechanical properties of the alloys.

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　The marginal contraction gap between dentin and restored composite resin was observed microscopically. Their shear bond strengths were also determined. Dentin was either treated or not by Gluma before the application of four different bonding agents, and restored subsequently by a microfilled composite resin.
　Marginal contraction gap as detectable in all cases without Gluma pretreatment. No significant differences were observed in regard to the four bonding agents applied. In these cases, the mean shear strength was 1〜3 MPa, in contrast to those of applied Gluma, 8〜15 MPa.

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　The relationship between dynamic mechanical properties and network-polymer structure of set materials made from hydrogen polydimethylsiloxane and vinyl polydimethylsiloxane, which had various characteristics such as molecular weight and the number of the functional groups, were investigated.
　Dynamic mechanical properties and network-polymer structure were measured by the dynamic shear test and the equilibrium swelling test.
　Storage modulus G' was in proportion to the network chain density ν and loss tangent tan δ was closely related to free-terminal chains remaining in the network structure of the set material.
　These results suggest that impression materials that have various properties suitable for any clinical situation can be formulated by giving proper molecular design for silicone prepolymers.

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　Three kinds of MMA-TBB resin, containing 5% 4-META, 5% Phenyl-P and 5% HNPM that have both hydrophilic and hydrophobic groups, and pure MMA-TBB resin were prepared. I investigated the relation between bond strength of these resins to 10-3 treated dentin, and the penetration into dentin of adhesion promoting monomers.
　Bond strength to dentin of MMA-TBB resins containing 4-META and Phenyl-P showed higher values (18〜19 MPa). SEM and TEM suggested that 4-META and Phenyl-P promoted monomers to penetrate into dentin, and concentrated on the subsurface layer of resin reinforced dentin, because the two methacrylates had good affinity for dentin powder. For Phenyl-P, bond strength was low when the dentin surface was not sufficiently dry.
　The concentration of 4-MET in the MMA solution influenced the bond strength to dentin and the highest value of 24.5 MPa was noted at 3%.

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