Polychlorotrifluoroethylene (PCTFE) resin was chosen to make a composite resin paste that contained a glass fiber. The paste was used as a restorative material, and was baked at 250〜280℃ for 1hr, after being applied to a metal frame of veneer or tissue surface of pontic. Technical work concerning this resin for restoration, mechanical properties, adhesive bonding strength between composite resin and metal after baking, were investigated. The technical work was performed easily. The tensile strength, elongation, elastic modulus, knoop hardness and bonding strength of specimens that contained 0.5g fiber in 10ml of PCTFE paste and were quenched in tap water immediately after baking, were 322kg/cm², 43%, 87×10²kg/cm² and 7.6, 150kg/cm², respectively;all of these except elongation were increased in the case of slow cooling. This composite resin is expected to prevent the accumulation of plaque or the adhering of staining substances in the oral cavity.

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To evaluate the surface reproduction of a dental stone model, measurement of the roughness of its smooth surface must be performed in combination with the reproduction test. Therefore, we developed a non-contact photogenic surface roughness analyzing system in which reflected light was used to measure roughness. Ra was found to decrease as the measured value increased. By the least square method, a negative correlation was found between the measured value and Ra. The appropriate angle between the light source of the system and the photodiode was found to be 160°. The results showed that this analyzing system can be used to evaluate the surface reproduction of a dental stone model when it is used in combination with the reproduction test.

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Pretreating agents were studied using bonding agents containing 2-methacryloxyethyl p-methoxyphenyl phosphoric acid (CH₃O-OH) and BPO-sulfinic acid initiator. A bonding agent containing 5wt% CH₃O-OH showed the high bond strength to EDTA-pretreated dentin as well as acid-etched dentin. Among various EDTA solutions, a 0.3M (pH 7.4) solution was the best for the pretreatment. A bonding agent containing 10wt%CH₃O-OH showed the highest bond strength (14MPa) to the dentin pretreated with this mild etchant for 60 sec.

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A hardening material was developed by mixing tetracalcium phosphate [Ca₄(PO₄)₂O] powder with citric acid [C₆H₈O₇] - malonic acid [C₃H₄O₄] solution. When mixed at a powder to liquid ratio (P/L) of 1.3 (g/g), this paste hardened within 3-4 minutes with its surface pH rapidly increasing to the neutral range. The strength of the hardening material was sufficient for dental and/or bone cement at P/L=1.3 and above. No apatite was detected in the hardening material by X-ray powder diffraction, however in distilled water its crystal structure was partially converted to apatite. This conversion was more rapid in phosphate buffer solution (pH=8.0); it occurred within one day, and the crystal structure of products was similar to bone apatite. The hardening material was slightly soluble (ca.2wt%) in distilled water. However the residue, which was amorphous, was also converted to apatite in phosphate buffer solution (pH=8.0). These results suggest the usefulness of this hardening material as a basic material of bioactive dental and bone cement.

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Bond strength of a dental adhesive resin cement with 20 commercial dental casting alloys was evaluated by tensile and three-point flexture tests. The specimens were stored in water at 37℃ for 24 fours before the tests. The alloys were also subjected to the bending test to determine the modulus of elasticity, elastic limit and 0.2% proof stress, and the relationships between these mechanical properties and the bond strength were examined. The bending bond strength expressed by the peeling debond force by bending was significantly different among the alloys used while no significant differences were found in the tensile bond strength. The debonding occurred in a manner of cohesive fracture through the cement in all cases. Multiple regression analysis showed that the peeling debond force was dependent on the 0.2% proof stress and modulus of elasticity of the alloys used, but that the tensile bond strength was independent of them.

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To investigate the relationship between the shape of adherend and the bond strength, tensile bond strength was measured using Ni-Cr and Au-Ag-Pd alloys of various thicknesses. The minimum and maximum bond strengths of Ni-Cr alloy were observed at thicknesses of 0.5mm and 3.0mm respectively. Bond strength was greater when a thin specimen was reinforced with adhesion. In a dry state, bond strength depended upon the thickness of the specimen but the values for Ni-Cr alloy and Au-Ag-Pd alloy were similar. The bond strength of hardened Au-Ag-Pd alloy was slightly higher than that after quenching but the influence of thickness was clearly observed.

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Self-setting apatite cement consisting of an equimolar mixture of tetracalcium phosphate and dicalcium phosphate dihydrate was found to set to a phase of hydroxyapatite when mixed with diluted phosphoric acid. The addition of hydroxyapatite to the cement greatly reduced the setting time to one acceptible for clinical application. Physicochemical properties such as crystallinity and wet compressive strength of set cement strongly depended upon nature of hydroxyapatite added as a setting accelerator. As crystallinity of added hydroxyapatite increased, the crystallinity of the set apatite cement increased. This finding makes it possible to prepare the most desiable self-setting apatite cement for different portion of hard tissues such as enamel, dentine and bone. The wet compressive strength measured when the set cement was stored in synthetic saliva decreased as the crystallinity of added hydroxyyapatite increased. Setting time and pH of the paste after spatulation, however, were negligibly affected by the added hydroxyapatite. In great contrast to the currently available cements, the self-setting apatite cement with components of particle size less than 37μm expands slightly, but notably during the setting reaction.

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The purposes of this study were to develop model materials for microwave polymerization and to evaluate the relation between the newly-developed model material and the adaptability of resin base dentures. Addition of aluminum powder at a concentration of more than 10wt% to the dental stone resulted affect the heating by microwave irradiation. When the aluminum powder was added to the model materials and to the investing plaster in the lower half of a FRP flask, the difference in temperature between the stone cast and the investing plaster in the upper half of the flask was increased by microwave heating and it became feasible to heat from the tissue side of the denture base. By the use of the newly-developed model materials and investing plaster, containing 20 and 30wt% aluminum powder, respectively, the adaptability of the resin base denture polymerized by microwave heating for 150 sec was by 20〜50% greater than that of denture made of conventional model materials and investing plaster.

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Pure titanium was casted with a newly developed CaO-Methanol investment. Castability assessed from the coiled wax pattern showed the highest value when the mold temperature was 1,000℃. Plate castings showed excellent surfaces without reaction with the mold, which surface roughness were 1.2〜1.9μm. The hardness of casting was about Hv 180 and hardened layers 10〜15μm thick were observed on the surface of castings with hardness of Hv 230〜250. Plate castings with high mold temperature (800℃〜1,000℃) showed few internal defects by X-ray examination.

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Machining properties of an electric discharge machine were compared with those of a milling machine using telescope denture. The milling machine with a carbide cutter produced a smooth surface on the precious metals whereas holes and grooves were easily produced with a steel cutter. However, the results were affected by pressure and vibration. For the base metal, the diamond cutter was useful for making the milling surface, but the surface was affected by the grain size of diamond. The steel cutter could not make holes or grooves on the base metal. The electric discharge machining could easily machine both precious and base metals, and their surfaces had a matte finish with many small spots. Holes and grooves could be machine precisely and very easily on both precious and base metals by the special electric discharge machining.

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The purpose of this study was to determine the tooth bond characteristics of a glass-ionomer cement. The effects of the storage time after extraction of experimental tooth, environmental humidity at setting and smear layer on the bond strengths of the glass-ionomer cement on human tooth were examined. Unlike composite resins, the storage time after extraction of experimental tooth had no significant effect on bond strengths of the glass-ionomer cement. This suggests that the in vivo and in vitro bond strengths of the glass-ionomer cement are similar. The bond strengths of the glass-ionomer cement to human tooth varied slightly with the environmental humidity. However this effect was much smaller than that seen in composite resins. The bond strengths of the glass-ionomer cement to dentin showed a slight increase with removal of smear layer from dentin surface.

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Cylindrical human enamel specimens were examined by the direct tensile test using the pinvise chuck built as a trial and the diametral test for indirct tensile strength. Tensile strengths were compared with the previously reported data on compressive strength of human enamel. The tensile strength, both direct and indirect, differed markedly according to the direction of enamel rods. The mean direct tensile strength was 21.9MPa in the direction of enamel rods axes V, 13.9MPa in the direction of crosss sectional longer axes of rods I, and 10.4MPa in the direction of H perpendicular to the directions of V and I. The mean diametral compressive strength was 45.6MPa in the direction of V, 37.7MPa in the direction of I, and 25.5MPa in the direction of H. The chucks to grip the test pieces were manufactured for trial and they were useful for the direct tensile test of enamel.

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This study investigated the effects of the addition of Au to NiTi alloys in order to improve their properties for medicine and dentistry. Ni-49.4Ti-4〜5Au (at%) cast specimens showed super-elasticity at 37℃, which allowed them to recover their shapes from the deformation of 3%, about ten times more than the strain of the proportional limit of Au-Pt alloys. Cast specimens consisting of Ni-49.4Ti-3Au (at%) and Ni-49.5〜49.6Ti-4Au (at%) recovered their shapes by heating to 55〜65℃. These alloys had adequate tensile strength and adequate elongation, and the amount Ni cations that dissolved from them was very small in 0.9% NaCl solution and 1% lactic acid.

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To improve the light permeability of the visible light-cured composite resin, the influences of the difference between refractive indices of monomer and filer, and the grain size of filler on the light permeability of light-cured composite resin were investigated by measuring depth of cure. When the refractive index of monomer approached that of filler, the depth of cure of composite resin approached the maximum. The refractive index of matrix resin, however, increased with polymerization of monomer. These results suggested that a monomer with about 0.012〜0.015 lower refractive index than that of filler was most suitable for the monomer component of the light-cured composite resin. When the size of filler was approximately of the same order of magnitude as the wavelength of the visible light, the depth of cure was minimum. This result suggested that the microfiller and the macrofiller were more effective filler component of the light-cured composites resin than the submicron filler. In addition, the light polymerization activities of the monomers used for experimental composite resins were evaluated by measuring the residual monomer in these cured resins by means of HPLC. The monomer with lower viscosity had higher reactivity than that with higher viscosity.

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The addition of calcium hydrogen phosphate (CHP) and calcium hydrogen phosphate dihydrate (CHPD) crystals to a dental stone (Fujirock) was found to improve mechanical properties of gypsum model materials. Crystal of calcium sulfate dihydrate of a hardened mixture propagated on the CHP and CHPD crystals, producing a precise network structure of the dental stone. The Bending strength and the surface roughness of the hardened mixture markedly improved.

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Co-precipitate mixtures containing zinc and aluminum hydroxides were prepared by either heterogeneous and homogeneous co-precipitation. The co-precipitate mixtures were washed and dried, and both ZnO and ZnAl₂O₄ were formed with firing.The particle size of ZnO increased with increased firing temperature and/or with increased amount of ZnO in the powder, while the particle size of ZnAl₂O₄ was relatively small, being less than 0.5μm.These ZnO-Al₂O₃ powders prepared by co-precipitation were applied to zinc phosphate cement. It was found that the ZnO particles reacted with the phosphoric acid faster than the ZnAl₂O₄ particles when the experimental cement powders were mixed with a commercial zinc phosphate cement liquid. The experimental cement powders containing a large amount of ZnAl₂O₄ showed slow setting time, low compressive strength and high disintegration. The powder containing a large amount of ZnO also showed the same results, because a low powder/liquid ratio was needed to achieve a standard consistency despite the large particle size of ZnO. Therefore, the experimental cement powders containing 30〜50wt% Al₂O₃ showed good results and met acceptance criteria(JIS-T-6602). However, the disintegration of the experimental cements was 2 or 3 times as large as that of the commercial zinc phosphate cement, and the surface of the experimental cements exhibited slow neutralization because of slow setting reaction. On the other hand, the solubility in citric acid or lactic acid was nearly the same as that of the commercial zinc phosphate cement.

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The propagating free radicals of self-curing resin for rebasing were examined by the electron spin resonance (ESR) technique. At 37℃, the propagating radical was first detected 5.5 minutes after mixing. The concentration of free radicals increased rapidly with time after 'so-called' induction time and reached the maximum level at 27 minutes. The free radicals thus formed were stable for more than 3,656 minutes, though the amount diminished gradually. With increased curing temperature, the maximum level of radical concentration decreased and the residual free radicals disappeared more rapidly. Radical concentration increased with an increase in the amount of activator of N, N-dimethyl-p-toluidine. The free radicals remained stable longer when mixed with a liquid containing less inhibitor of hydroquinone.

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New type composites composed of methyl methacrylate and rigid siloxane polymers, which have a ladder-like structure, have been developed for denture base resins. The Polymers prepared at various rations of 3-methacryloxypropyl trimethoxysilane and phenyl triethoxysilane were white powder, with molecular weights of 10,000 to 20,000. Compressive, diametral tensile and bending strength of the various PMMA composites which contained 10 to 15wt% of the siloxane polymers, were 20 to 40% higher than those of polymethylmethacrylate. However, the bending strength and bending modulus of PMMA composites were 20 and 15% higher, respectively than those of the copolymers with same amount of polyfunctional monomers, such as TMPT and Bis-GMA. In view of the degree of crosslink in the various copolymers and the structures of siloxane bond, it is speculated that the copolymer is reinforced not only by cross-linkage with the olefinic double bonds, but by the contribution of rigid ladder structure of the siloxane polymers. The results suggest that the molecular composites of the siloxane polymer-PMMA can be extended to denture base resins.

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Reciprocation of wheels in electro-mechanical grinding was investigated with a handier tool. Vitrified wheels and resinoid wheels with smaller grains were used. Co-Cr alloy and Ni-Cr alloy were ground using various current densities and the grinding surface texture was examined. The mechanical grinding with reciprocation of vitrified wheels with smaller grains showed better surface textures for both alloys, but the effect of current density on the electrolytic polishing surface differed between the two alloys. The electro-mechanical grinding surface was affected by the grinding load, and the effect of the mechanical grinding surface appeared at a load of 500g and the effect of the electrolytic polishing surface in the load of 100g. Resinoid wheels were found to be inferior to vitrified wheels for the electrolytic polishing but had some advantage in manufacturing. The electro-mechanical grinding with reciprocation of wheels was found to be a more practical method with respect to both the amount of grinding and the surface texture when the grain size of the wheel, the grinding load and the current density were set suitably.

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