A lever type testing apparatus was devised to evaluate the grinding performance of tools. Grinding of a Co-Cr alloy for three successive hours was performed under dry conditions to investigate the performance life of three vitrified bond wheels on the market and experimental electrodeposited wheels of CBN and diamond. The grinding behavior was determined by analyses of workpiece- and handpiece-vibrations and mandrel whirling, and observations of grinding chips, wheel loading and wear. Alumina wheels tended to stop grinding suddenly at a wheel rotation speed of 24,000 rpm or gradually at 12,000 rpm, which produced grooves due to attrition of abrasive grains on some localized areas of the wheel surface. When the height of the workpiece was high at 12,000 rpm or even low at 24,000 rpm, the vitrified bond wheel tended to strike against the workpiece at short intervals, causing self dressing of cutting edges. Under high grinding force and at high rotation spped, the diamond wheel exhibited very remarkably high performance at the initial stage of grinding, however the grinding rate decreased extremely with time. The loss of performance was attributed to a change of plated Ni-P alloy sustaining grains. On the other hand, the performance of the CBN wheel was relatively high. The grinding rate showed little change after three hours of grinding.

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This study examined the effect of the polymer/Sn composite plating on adhesive strength of Panavia EX and Super Bond C & B to type IV gold alloy. A cationic surfactant was found to be necessary for providing a sufficient amount of polymer particles in the Sn plating bath. The adequate particle size range was 0.5〜1.0 μm. The adhesive strength using polymer/Sn composite plating was increased by 70〜80%. The maximum adhesive strength was obtained when the polymer concentration in the plating bath was in the range of 5〜10%, but the adhesive strength was little influenced by the different polymers.

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This study investigated the treatment of metals for obtaining firm adhesion between the adhesive resin, Panavia EX and Super Bond C & B, and the various dental alloys. The effects of poly vinyl chrolide (PVC) concentration in Sn-plating solution on adhesive strength of the adhesive resins to gold alloy type IV, 12% Au-Ag-Pd and Ni-Cr were also examined. The maximum adhesive strength to gold alloy type IV was obtained when the polymer concentration in Sn plating solution was 3〜5%. The PVC/Sn composite plating had similar effects on adhesive strength to 12% Au-Ag-Pd alloy and Ni-Cr alloy. The contact angle of water and BMEPP against the dental alloys treated with plating was influenced by the polymer concentration.

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An adhesive self-curable opaque resin was developed using poly (methyl methacrylate) coated titanium dioxide, 4-methacryloxyethyl trimellitate anhydride and tri-n-butylborane derivative. Uniformly encapsulated particles were obtained by three-step polymerization of methyl methacrylate in the presence of surfactant-adsorbed titanium dioxide with potassium persulfate. The opaque resin showed better mechanical and handling properties than that with uncoated titanium dioxide, and it could be used as transparent 4-META/MMA-TBB resin. 4-META/MMA-TBB opaque resin bonded strongly to surface-treated dental alloys. It could be used for bonding veneering resin to metal frameworks and for seating resin bonded fixed partial dentures to enamel surfaces.

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When α-tricalcium phophate (α-TCP) powder is mixed with a polycarboxylic acid solution, an α-TCP-polycarboxylic acid complex is formed and hardens. The purpose of this study was to investigate the influence of various additives on the physical properties of α-TCP-polycarboxylic acid complexes as a basic study of new calcium phosphate materials incorporating α-TCP. Ground α-TCP powders were mixed with various additives. ZnO, MgO, ZrO₂, TiO₂ and α-Al₂O₃ were used as the additives. The mixing liquid for dental polycarboxylate cement (HY-BOND polycarboxylate cement, Shofu) was polycarboxylic acid solution. After the α-TCP powders, each containing a different additive, were mixed with the polycarboxylic acid solution at a powder/liquid ratio=1.2/1.0 (g/g), the setting time, compressive strength, and solubility and disintegration of the complexes were measured by the methods specified by ADAS No.61 for zinc polycraboxylate cement. Also, the complexes were analyzed by X-ray powder diffraction analysis and observed with a scanning electron microscope. The addition of the individual oxides to the complexes generally increased the setting time, especially in the case of ZnO. Although the presence of a small amount of additive in the complexes slightly increased the compressive strength, it was impossible to increase significantly the strength by the addition of the oxides used in this study. The addition of ZrO₂ or TiO₂ decreased the solubilty and disintegration of the complex;however, that of ZnO or MgO increased the solubility and disintegration. X-ray diffraction analysis of the complexes showed amorphous patterns and the unreactive α-TCP and/or additives were identified. Scanning electron microscopic observation indicated that the complexes consisted of a matrix and unreactive α-TCP and/or additive particles. The results suggest that the presence of additives that react rapidly with the polycarboxylic acid solution remarkably affected the setting reaction and physical properties of the complexes.

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Mechanical properties of seven kinds of light cured composite resins were measured to evaluate the environmental durability in water after storage in distilled water at 37℃ for 2 months. Water sorption of all composite resins increased rapidly within 1 week and then increased gradually for 2 months. This water uptake was thought to be involved in the physical or chemical deterioration of composite resin material. The tensile strength of all composite resins measured by the direct tensile test reached the maximum value after 24 hours but decreased significantly after 2 months and became the 55〜75% of their maximum values. However, the rate of decrease differed with the commerical resin. The diametral strength and the compressive strength of most composite resins reached equilibrium after 1 week with no further decrease. The direct tensile test was found to be useful to evaluate the environmental durability in water in a relatively short period.

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Using three commercial phosphate bonded investments and one commercial cobalt-chromium alloy, factors that influence casting stress were investigated. Casting stress was affected significantly by the mold temperature. Casting stress was also affected by cooling shrinkage, strength of the mold, cooling rate and sand burning at mold temperatures of 900, 650, or 450℃. Casting stress with 20℃-mold was affected chiefly by the strength of the mold.

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Everbright was developed as a glazing material for light cured direct relining meterial Eporex-R. We examined whether this material can be applied to denture base resin as a glazing and hardening material.Analysis of hardness, smoothness, abrasion resistance, water resistance, weathering resistance and durability revealed that this material had coating effects to the same degree as conventional ultraviolet rays cured glazing and hardening materials. These results suggest that this material can be applied to denture base resin as a glazing and hardening material.

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This study investigated the best conditions for adhesion between dental casting alloys and thermosetting resins.Four commercial alloys(Au alloy, Ag-Pd-Au alloy, and two Ni-Cr alloys)and a visible light-cured and heat-cured thermosetting resins were used.The interface between alloy and resin was analyzed by EPMA.The adhesive strength between alloy and resin was measured after sand blasting or acid etching treatment, and the strength of adhesion after thermal cycling was also examined.Tight adhesion between alloy and resin was observed after both sand blasting and acid etching treatments.The adhesive mechanism was principally mechanical, since no interdiffusion layer of elements composed of alloy and resin was observed by EPMA.The surface treated with sand blasting was effective for the mechanical bond between alloy and resin.The adhesive strength increased with decreasing thickness of the opaque resin layer.The adhesive strength remarkably decreased by increasing the number of thermal cyclings.

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Physical and chemical properties of tetracalcium phosphate(4CP)and α-tricalcium phosphate(α-TCP)cement were compared.4CP or α-TCP was mixed with 45% citric acid solution at a powder-liquid ratio of 1.5(w/w).To determine the acidity of the cements, changes in the pH of 0.5ml of distilled water in contact with each cement surface was monitored.4CP cement gave the highest pH, ranging from 4.75 to 5.23, among the 4 types of cement tested.The measured pH values of α-TCP and polycarboxylate cements were 4.02 to 4.22 and 4.14 to 4.62, respectively.On the other hand, zinc phosphate cement showed strong acidity, (pH3.29 to 3.62).These in vitro results suggest that 4CP cement is irritative to the dental pulp.The compressive strengths of both 4CP and α-TCP cements, (50.0 and 74.9MPa respectively), fullfilled the requirement of ADAS No.61 for polycarboxylate cement.Under the same conditions, it was shown that 4CP and α-TCP cements had high solubility(1.8 and 4.0% respectively)which were inferior to the standard.When immersed in phosphate buffered saline, 4CP and α-TCP cements also showed high solubility but no changes in the compressive strength for 7 days.

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Ti-Ni implants were coated with oxide film to suppress dissolution of Ni, and the corrosion resistance was estimated by means of anodic polarization measurement in 1% NaCl solution.By coating, dissolution at low potential was suppressed and the dissolute current density decreased.A further decrease in current density, which results from stabilization of the passive state on the surface, was observed by repeated polarization.In addition, the oxide film showed close adhesion with matrix, and did not form cracks or peel off by plastic deformation associated with the shape memory effect.The surface was scratched to simulate accidental break in coating film, and polarization measurement was carried out.However, no dissolution at low potential was observed, and a stable surface was maintained.

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The compositions of four proprietary tissue conditioners were investigated by infrared spectrophotometry.The effect of polymers and plasticizers on the dynamic viscoelastic properties of tissue conditioners were examined using two proprietary polymer powders(polymethacrylate and vinyl chloride-vinyl acetate copolymer)and four plasticizers.The proprietary liquid was a mixture of a phthalic ester plasticizers(such as butyl phthalyl butyl glycolate, dibutyl phthalate, benzyl butyl phthalate)with up to 20% ethyl alcohol.The phthalic ester plasticizers used in common proprietary liquids did not appreciably affected the storage modulus G′ and dynamic viscosity η′ of tissue conditioners.The factor influencing the dynamic viscoelastic properties of materials was the structure of the polymer powder.

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Light-cure composite resins containing RDMA in the monomer and TMPT filler in the filler were prepared.The mechanical properties, adhesion to bovine dentine, and contraction gap were studied.Brinell hardness was found to be maximum when the filler contained 30wt% TMPT filler, and abraded surface became smoother because of TMPT filler.However, compressive strength, amount of water sorption, and coefficient of thermal expansion depended on the weight of inorganic filler such as RM50.The amount of residual monomer was minimized in the mixture of TEGDMA, RDMA in the monomer and TMPT filler, RM50 in the filler.Tensile bond strength to dentine was only 2〜3MPa, because of polymerization shrinkage of composite resin.However, it was improved by Super Bond.Contraction gap was slightly better with a bonding agent and much better with Super Bond as a bonding agent than without a bonding agent.

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Barrel finishing of titanium castings using the centrifugal barrel machine was performed and polishing efficiency and surface texture were examined.Centrifugal barrel finishing was found to be very efficient for polishing and finishing titanium castings in a short time.Barrel finishing with media for coarse finish resulted in a large amount of polishing but also caused wear of the edge of the specimen.Barrel finishing with media for medium and final finishing after the medium finishing, performed using convention rotation grinding wheels, was found to be useful for dental use to obtain a good surface texture while maintaining dimensional fitness.

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