It has been reported that this alloy exhibits excellent mechanical and fatigue properties through conducting solution treatments at high temperatures of over 800℃. Regarding this hardening mechanism, there is a solid solution hardening theory, in which the Ag-Cu α₁ phase and Pd-Cu β phase become a solid solution in the α solid solution phase that exists near the melting point, starting at 800℃, and also theories based on precipitation hardening. In light of the foregoing, we conducted heat treatment in an air atmosphere and examined the Au-Ag-Pd alloy hardening mechanism. We believe the results show that both the Ag-Cu α₁ phase and Pd-Cu β phase become a solid solution in the a solid solution phase, and theories based on precipitation hardening with regard to the precipitation of the semi-stable β' phase of the L1₀ type structure during cooling are contributing to hardening in a complex way.

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As part of a study on the disinfection of impressions, the present study investigated the effect of disinfecting agar/alginate combined impressions on the dimensional accuracy of stone dies. Nine combined impressions were prepared using combinations of 3 brands of cartridge-formed agar impression material and 3 brands of alginate impression material. The impressions were disinfected in two ways: immersion in 1% sodium hypochlorite solution for 10 min, and storage for 10 min in sealed bags after spraying 1% sodium hypochlorite. Stone dies obtained from the non-disinfected impressions were also prepared as a control. The disinfection of combined impressions decreased the dimensions of resultant stone dies. However, it did not cause the deformation of stone dies except for in one combination of agar and alginate impressions.

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We examined the role of the spongy structure of the lower jawbone where an implant was placed. To evaluate the effect of the microstructure, the voxel FEM was used. The loading condition suited a biting motion, where the forces produced by six muscles were measured. The results of analysis showed that stress around the implant was widely distributed not only in the cortical bone but also in the cancellous bone. It was noted that the amplitude of the stress concentration in the cortical bone around the implant was extremely reduced, almost to one quarter, by the structure of the bone trabeculae.

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We measured the bonding strengths of luting cements to polished titanium surfaces using both tensile and shear bond tests. Seven kinds of luting cements (poly-carboxylic and resin-based cements) were investigated. Relationships between the tensile bond strength (TBS) and shear bond strength (SBS) were evaluated. The fractured surfaces after the tensile bond test were observed, and the tensile strengths of luting cements were also measured. The bonding strengths of resin-based cements were higher than those of poly-carboxylic cements, and the tensile strengths of resin-based cements were also higher. SBS was significantly higher (1.6〜5.9 times, mean: 3.4 times) than TBS, and the relationship between TBS and SBS showed a different tendency with each type of cement. We concluded that only the measurement of the bonding strength was not sufficient to evaluate the bonding characteristics of luting cement. When we compared different type of cements, observation of the fracture mode and measurement of the tensile strength of luting cements were also necessary for exact evaluations.

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In this study, the adsorption force was compared between titanium cast denture bases and Co-Cr alloy cast denture bases by measuring the adsorption force of dentures to the stone model, which was wetted as a model of the oral cavity. For the measurement of adsorption force, the stone model was immersed in water, and a tension test was performed at crosshead speeds of 50, 100, and 150mm/min using a universal testing machine. The contact angle between titanium or Co-Cr alloy and water was measured using a goniometer. Titanium cast denture bases showed a slightly higher adhesion force than Co-Cr alloy cast denture bases. The contact angle to water was 71°for titanium, which was smaller than 80°for Co-Cr alloy, showing better wetting.

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The effect of powder-liquid ratio on shear strength of glass ionomer cements for luting was examined. Four commercially available glass ionomer cements for luting with different setting modes (conventional and resin-modified types) were used. After each glass ionomer cement was mixed at three different powder/liquid ratios, disk shape specimens (10mm in dia., 1.0mm in thickness) were prepared respectively. Specimens were immersed in deionized water at 37℃ for 24 and 168 hours and the shear strengths of specimens were determined using a punch tool. The Weibull moduli of strength data for the specimens were also estimated. The change in mass of cement specimens were recorded before and after storage in water. The volume of matrix phase in set cement was estimated using image analysis. A trend was seen whereby a lower powder/liquid ratio decreased the strength and increased water sorption, probably due to a change in volume of matrix phase in cement. Weibull analysis showed that no significant differences in the Weibull moduli of strength data were observed among all mixing conditions tested. This suggested that the change in mixing ratio of cement did not notably affect dispersion of shear strength data.

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The aim of this study was to assess how the ratio of regular composite resin to the thickness of flowable composite resin affects bi-axial flexure strength, the apparent degree of elasticity, and fracture mode in laminated dental composite resin disc specimens. Regular composite resin: the flowable composite resin thickness ratio influenced bi-axial flexure strength and the apparent degree of elasticity. Strength and degree of elasticity for regular composite resin: flowable composite resin thickness ratios of 1.8:0.2 and 1.6:0.4 were higher than that for regular composite resin alone. The fracture mode was homogeneous, and no defects or voids were observed at the interface between the regular composite resin and flowable composite resin. These results suggest that the stronger regular composite resin should be used at the greatest thickness possible, and that the weaker flowable composite resin should be as thin as possible.

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The effect of light intensity on the Weibull moduli of the bond strength of resin cements to ceramic was examined. Cement rods of two dual-cured resin cements [Panavia F 2.0 (Kurarey, A), Bistite II (Tokuyama Dental, B)] were bonded to ceramic plates using a halogen light-curing unit at an intensity of 300 or 800mW/cm². Non-irradiated specimens served as controls. The shear bond strengths (n=12 each) of the cements were determined at 10 minutes and 24 hours after preparation and their Weibull moduli for bond strength data were calculated. The Weibull moduli for cement A noticeably increased at 800mW/cm². A trend was seen in cement B whereby Weibull moduli decreased as time elapsed. Depending upon the products, light irradiation appeared to reduce dispersion of the bond strength data at the initial stage of ceramic bonding.

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