This study focused on establishing casting conditions for a high casting rate using the Ti-6Al-7Nb alloy for dental practice application. This report describes the investigation of the conditions affecting the casting rate, such as the pattern thickness, and the melting time and weight of the alloy, using a casting machine with a spin cast system and magnesia-alumina cement investment material. Regarding the relationship between the pattern thickness and the casting rate, the rate increased significantly as the sheet wax became thicker, at 0.30<0.36<0.46mm. At a thickness of 0.46mm, the casting rate increased to 100%. Regarding the ralationship between the melting time and the casting rate, the rate increased significantly as the melting time became longer, at 60<70<75 seconds. Meanwhile, regarding the relationship between the melting weight of the alloy and the casting rate, the casting rate at the weight of alloy of 30g was higher than that at 40g.

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The aim of this study was to investigate the influence of the position of fiber-reinforced composite (FRC) on the flexure strength of the complex of FRC and hybrid composite resin. The complex of FRC and hybrid composite resin was fabricated with three different FRC positions : upper FRC position, central FRC position, and lower FRC position. The complex of FRC and hybrid composite resin was used as a sample in this study, and the stress value was calculated by a three-point bending test. The lower FRC position showed a significantly higher flexure strength (p<0.01) compared with those of the upper FRC and central FRC positions. There was no significant difference between the upper FRC position and the central FRC position. It was shown that it is desirable to set the FRC position lower when applying FRC to a bridge.

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To clarify leaching levels of di-2-ethylhexylphthalate (DEHP) from gloves made of polyvinyl chloride (PVC) used to prevent an infectious disease by treatment of dentistry into the saliva, one side of disc-shaped specimens of PVC gloves was put in contact with human saliva, and then the quantity of leached DEHP and its metabolite, mono-2-ethylhexylphthalate (MEHP) was determined using gas chromatography/mass spectroscopy. The maximum quantity of DEHP detected after glove contact for one hour with saliva was approximately 1.4 μg/cm², while that of MEHP was approximately 0.47 μg/cm². The quantity of elution varied depending on the contact time with saliva and with the kind of PVC glove used.

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In this study, the effects of the pulse number, energy intensity and irradiation distance of the laser on temperature rise were examined using the dental treatment Nd : YAG laser apparatus. The effects of air-blowing or water-spraying on temperature rise were also investigated. Furthermore, the effect of laser-welding metal to the cast crown on the temperature rise of the human dentin was studied. The increase in both the pulse number and the energy intensity of the laser allowed for an increase in the temperature of the irradiated spot. The application of water-spray cooling resulted in sufficient prevention of the temperature rise of the laser-irradiated spot during irradiation, when compared with that by air-blow cooling. When the metal was laser-welded to the cast crown that had set on the tooth, the maximum temperature rise of the human dentin was only 7℃. These results suggest that intraoral laser-welding without any damage to dental pulp is possible.

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This study examined the effect of surface roughness of the ceramics on the shear bond strength between ceramic and resin composite repair systems after thermocycling. Four commercially available repair systems with and without fillers were tested. Disc specimens of ceramic for metal-ceramics were prepared, and finished with either #120 or #600 SiC abrasive paper. A light-cured resin composite rod was bonded on the ceramic surface using one of the repair systems. The specimens were immersed in deionized water at 37℃ for up to 6 days or thermocycled for 2, 000 cycles in deionized water between 4℃ and 60℃. All of the specimens had lower bond strength values after thermocycling. The bond strengths of the specimens finished with #120 paper were greater than those finished with #600 paper in both repair systems. Under the present conditions, a coarser ceramic surface could be more advantageous for resin composite adhesion when repair systems without fillers are used.

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Titanium surfaces were treated with hydrogen peroxide solution for different amounts of time. Then, one resin sealant and three types of adhesive resins were bonded on the treated surfaces. Color changes, bond strength, and fracture bond toughness were investigated as functions of immersion time. Also, the treated surfaces were examined using a scanning probe microscope. The main conclusions were as follows : 1. As the immersion time was prolonged, the surfaces became less bright and exhibited a brownish color. 2. The resin sealant exhibited maximum bond strength when the surface was treated for 60 min. 3. Great improvements in bond strength were found when adhesive resins were bonded on the 60 min-treated surfaces in comparison with untreated surfaces. 4. Both the 30 and 60 min-treated surfaces revealed fine, uneven-shaped oxide film, while such irregularities were not observed on the 120 min-treated surface. The micro-anchoring effect of uneven surfaces seems to contribute to improved bond strengths.

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This study examined the surface roughness of dental stone models prepared by alginate impression materials and dental stones, after the models were immersed in commercial disinfectant solutions containing potassium sulfate. The test results indicated that the value of surface roughness of dental stone models immersed in disinfectant solutions containing potassium sulfate added to Agusa TB or Cidex plus was significantly smaller than that of the models immersed in solutions without potassium sulfate. It was found that the dental stone models immersed in disinfectant solutions containing potassium sulfate could be used clinically, because their value of surface roughness ranged from 1.10 to 1.83 μm. Consequently, it was suggested that disinfecting dental stone models with immersion in commercial disinfectant solutions containing potassium sulfate is useful for decreasing the surface roughness of dental stone models.

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