We prepared a new disinfectant-fixing solution for alginate impressions (NCK solution) composed of l.O% NaClO-0.2% CaCl₂-1.0% K₂SO₄. In this study, we investigated the dimensional stability of alginate impressions and changes in pH and ion concentration of the solution. For comparison, we used four different commercial alginate impression materials. The mean dimensional change of the four impressions obtained 60 min after immersion of a single oblong plate impression measuring 3 cm³ was -0.068%, and was increased by 0.082%, after four pieces of impression materials (12cm³) were immersed. The mean dimensional changes in two pieces were within the acceptable limit for clinical use (±0.2%). However, dimensional changes were not within acceptable limits in two of the impression materials. For such impressions, appropriate disinfectant-fixing solutions especially prepared for use with those materials should be used. The pH and residual chlorine in the NCK solution were 8.91, 7.21mM, respectively. Kinetic study revealed that concentrations of Ca and K ions and residual chlorine contained in the NCK solution were gradually reduced after immersion of the impressions or when a larger proportion of each impression was immersed. These results suggest that Ca and K ions contained in the NCK solution were adsorbed by the impressions.

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To modify the properties of PMMA/MMA-TBB resin, the influences of blending PMMA small beads (MB8) with a pulverized PMMA powder (SB) were studied by measuring setting time, working time, cement film thickness, and bond strength to dentin. The MB8/SB blends demonstrated the following qualities compared with SB powder alone :(1) setting time and working time were increased ;(2) film thickness remained thin over a long period ;(3) mean bond strength to dentin was the same but the lower limit of the range was increased. Thus, the PMMA blends were suggested to be a useful MMA-TBB resin cement providing improved clinical performance.

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JIS class 2 titanium of φ 2mm wiry specimens was welded by 4 types of welding methods. Strength of the welding regions was assessed by tensile tests of these specimens. Methods of welding were laser welding (A) and Tig weIding (B) both with provisional joining by laser welding. Each of these weldings was carried out under two conditions. One was direct welding, in which the surfaces were tightly fixed to direct contact. The other condition was indirect welding, in which the jointing surfaces were tightly fixed intermediate material consisting of a round Titanium plate φ 0.25mm thick. For Laser welding, Nd Yag Laser welding-machine (Dentaurum Co., DL 2000) and for the Tig welding, a conventional Tig welding-machine Inverter (Hitachi Co., Tig 300 NSII) in the Titanium casting machine were respectively used. The highest welding strength with small deviation was observed in the group treated by direct laser welding. In the Tig welding group, there was no significant difference in the strength between direct and indirect welding. There was no significant difference between Tig welding groups and indirect laser welding. It was suggested that jointing surfaces cut rectangularly should be tightly fixed with a jig for the elimination of transverse distortion during the welding procedure. These results may indicate that more amount of molten titanium pool flows under Tig welding than under the laser welding. Tensile strength of the welded region after laser welding was generally higher and more constant than that achieved by the Tig welding.

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With cast and wrought specimens made of CP titanium and Ti-6Al-7Nb dental alloy, elongation and strain of the specimens during tensile test were evaluated using a video extensometer. The strain evaluated by a video extensometer and that estimated from movement of actuator of the test machine were compared. As the resuIts, it is confirmed the former is applicable to evaluate the strain, and the latter ought not to be used as the experimental data. By comparison of both strain measurements, phenomenon, such as sliding between grip wedge/specimen during the early stage of the tensile test and reduction of specimens'area during the last stage of the test, was found out. The initial sliding was greater for harder specimens, i.e. for Ti-6Al-7Nb alloy than for CP titanium. The strain evaluated from the video extensometer apparently became larger than that from the actuator, when the area of the specimens was reduced during the last stage of the test.

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Fatigue test is a requisite for the application of titanium and titanium alloys as a dental casting material in addition to tensile test, hardness test, and others. It is considered that corrosion fatigue test is important because dental prosthesis is generally used in the oral cavity. In this study, corrosion fatigue property in 0.9% NaCl solution using corrosion fatigue test equipment of Ti-6Al-4V alloy and Ti-6Al-7Nb alloy dental castings was investigated. As a result, the corrosion fatigue property of Ti-6Al-7Nb alloy castings was good, and that it is practical for use as a dental material.

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Bonding of MMA-TBB resin to 10% citric acid etched dentin was investigated. The permeability of the dentin was improved by Triton X-100 (TX) and 5% glutaraldehyde in ethanol (GA/EtOH) which can immobilize water-soluble proteins in the demineralized substrate. Measurement of tensile bond strength and SEM observation of fractured surfaces were carried out. When demineralized dentin was treated with TX, the bond strength was 0.8 MPa and adhesive failure was identified. However, when treatment with GA/EtOH was added after TX, the bond strength increased significantly to 13.9 MPa (p<0.05) and the fracture mode changed to cohesive failure in the cured resin. It was concluded that the bonding became possible by the double pretreatment. Glutaraldehyde immobilized the water-soluble proteins. The MMA could be impregnated into the dentin and polymerized in situ forming the hybridized dentin.

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The bonding durability of four kinds of metal-resin veneers to a Ag-Pd-Cu-Au alloy was evaluated by the shear bond strength and impact resistance. The surface of cast alloy was treated with only Al_2O_3 sandblasted on polished surface or applied to the beads before casting. Then resin veneers φ 6×2 mm were fabricated according to the manufacturer's instructions. Specimens were stored in water at 37℃ for 24 hrs as a control and 30 days or thermocycled for 5,000 times between in water baths of 4℃ and 60 ℃. The results indicated that when treatment was applied to beads, bonding strength and their durability was effectively improved. After immersion for 30 days, the shear bond strength of the two kinds of veneers was higher than that of the control. The fractography after impact test implied that cracks initiated in the opaque resin and propagated into or along the interface between the resin and the alloy. From results of the flexural test and of previously described, it was suggested that the opaque resin was not cured sufficiently and has poor mechanical properties compared to those of the body resin. The degree of conversion of the opaque resin and the wettability between the resin and the filler should be improved to increase the bonding durability of metal-resin veneers.

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The influences of primers and dentin conditioning on bond strength of PMMA/MMA resin to dentin were studied using an initiator system consisting of barbituric acid, copper salt and quaternary ammonium chloride. While N-(2-methacryloxythyl)-2-pyrrolidone primer produced higher bond strength than HEMA primer, HEMA primer containing glutaraldehyde (Gluma) gave the highest bond strength. Pretreating dentin with 10% phosphoric acid containing 3% copper chloride (10 P-3 Cu) for 30s followed by rinsing with water for 30s produced significantly higher bond strength than the same conditioning for 10 s each regimen. The highest bond strength to dentin of PMMA/MMA resin, formulated with 2% 1-cyclohexyl-5-ethylbarbituric acid, 0.003% copper acetyl acetonate and 0.06% vinylbenzyltetradecyldimethylammonium chloride, was obtained after pretreating dentin with 10P-3Cu for 30 s and rinsing with water for 30 s followed by application of Gluma.

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The 3-point bending test specified by ISO 6875: 1995 for resin-based filling materials and that by the ISO 4049:1988 for dental ceramics were employed to evaluate the effects on the flexural properties of dental restorative materials. A Ag-Pd alloy, a Ag-Sn alloy (JIS type 1 silver alloy), a Ag-In alloy (JIS type 2 silver alloy), two castable ceramics, a ceramic block for CAD/CAM, a composite resin for filling, two composite resins for veneering, a composite resin for core build-up, and a composite resin block for CAD/CAM and bovine dentin were examined. Flexural strengths of the Ag-Sn alloy and one of the castable ceramics obtained from two test methods were significantly different:flexural moduli of two castable ceramics, photo-curing composite resins and the photo-and chemical-curing composite resin obtained from two test methods were significantly different. The reasons for these discrepancies were considered because of the heterogeneity of the surface and the inside of castable ceramics and the effect of specimen geometry on the conversion ratio of composite resins.

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