It is thought that porosity in a laser spot weld metal is due to a remnant of gas produced by closing of the top surface mouth of the keyhole generated during welding, and that the pulse shape influences the porosity formation tendency. Therefore, the formation of porosity was examined in welds made with rectangular pulse shapes. Cobalt-chromium alloy and CP titanium were used for this study. Spot welds were formed by irradiation with single pulsed YAG laser under various parameters of output power, pulse width and defocused distance. Then, the penetration geometry and porosity were observed and measured. Porosity was more easily formed in spot welds of cobalt-chromium alloy than CP titanium. It was confirmed that if the penetration depth was 1.5mm or less in the CP titanium, the formation of weld metals without porosity was possible. However, it was difficult to obtain a deeply penetrated weld metal without porosity in the cobalt-chromium alloy.

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The purpose of this study was to develop a temporary luting agent with excellent handling and with suitable bond strength which, in addition, would leave less of a remnant after the removal of a temporary restoration from the abutment. The basic composition of the experimental material (PEE) was polyethylmethacrylate (PEMA) powder and eugenol oil. The powder/liquid ratio varied from 1.0 to 1.6. The controls used were commercial temporary luting cements. The follwing results were obtained; PEE 1.6 had high consistency, high film thickness and low water solubility compared with PEE 1.0〜1.4. No sighnificant difference was observed in bond strength between self-curing resin crown and stainless die abutment when comparing PEE 1.6 and the control after the thermal cycling test. Observations of the interface of the adhesion specimen showed that PEE 1.6 did not remain on the die abutment. From the results, it was concluded that PEE 1.6 was suitable for clinical use.

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Titanium (Ti) is active metal. However, Ti has an ability to protect itself against chemical attack by a passive oxide film. The nature of the oxide film is an important factor in determining chemical reactions of Ti. Pure Ti was annealed in ambient air at 800℃. The oxide films of the specimens were removed by abrasion. The specimens were immersed in a mixed solution of NaF and H₃PO₄ (APF). The effect of oxide films on degradation of Ti in APF solution was measured by a thermal desorption spectrometer (TDS). The dislodgement of ions from the specimens during heating was detected. The amounts of released hydrogen were estimated for the specimens with the heat and the immersion treatments. The oxide films were an effective factor in determining the degradation of Ti in the APF solution. The TDS method was a useful technique for identification of the absorbed molecules.

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Four kinds of combination of molds simulating inlay or crown and cavity or abutment with different thermal expansion coefficients were attached by means of four dental luting cements, i.e. zinc phosphate cement, polycarboxylate cement, glassionomer cement, and resin cement. Film-thickness was calculated from the difference between cemented molds. The adhesive strength was measured by tensile adhesive test after 1000 thermal cycles performed 10 minutes after mixing by immersing into a 5℃ and 55℃ water bath for 30 seconds each, and a 60kgf load was applied twice for 10 seconds during each immersion in the case of load applying conditions. Resin cement showed the largest adhesive strength, polycarboxylate cement was second, and zinc phosphate cement and glassionomer cement were about equal. A low adhesive strength was observed when the inner mold was made of stainless steel (SUS) and the outer mold was made of low expansion alloy Inver (INV). In the case of crown made of INV, the adhesive strength was large when the load was not applied during thermal cycles, and conversely in the case of crown made of SUS, the adhesive strength was large when the load was applied. Film thickness of inlay was greater than that of crown.

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The aim of this study was to investigate the reinforcement effect of the position and diameter of a glass fiber post on the strength of resin composites in core build-up by insertion of a glass fiber post. Three different cured-type resin composites for core build-up and three different diameters of two different brands of glass fiber post were tested. Rectangular specimens, in which either the post was placed into the upper side (compressive side) or the lower side (tensile side), were fabricated and subjected to the 3-point bending test. In addition, the fracture resistance of the resin composite core with fiber post placed in human extracted premolar was determined. Significantly greater flexural strength was observed in the specimens in which the post was placed in the lower side than in those with it placed in the upper side (p<0.05). A trend was seen that the larger the diameter of the post, the greater the flexural strength in the 3-point bending test and the fracture resistance of the resin composite core in extracted teeth.

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The development of antibacterial dental resin using the silver methacrylate monomer (MAg) as an antibacterial substance was tried. The solubility of MAg in methyl methacrylate (MMA) was examined, and then the mechanical property of the polymer obtained by polymerization of MAg-containing MMA was tested. As a result, MAg was dissolved into MMA at a concentration of 84μmol/l, and it was suggested that the concentration was sufficient for the appearance of antibacterial activity. The resin obtained was transparent and colorless, and there was no esthetic problem. The compressive and bending strength of the resin were not significantly different compared with those of PMMA.

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