Dental investments were developed using the expansion originating from thermal decomposition and crystal growth of decomposed phases of a new aluminum phosphate compound, aluminum phosphite Al₂ (PHO₃)₃. The thermal decomposition of aluminum phosphite was investigated thermoanalytically together with X-ray diffraction and gas-chromatography. The thermal dimensional changes of gypsum-bonded investments containing aluminum phosphite were measured. The aluminum phosphite, which had decomposed by 400℃, expanded as the temperature increased, while transforming to crystal growth of aluminum orthophosphate and aluminum methaphosphate, which took place when heated further, contributed to a large expansion of the investments. Since the amount of thermal expansion could be regulated without any difficulty, it would be possible to develop dental investments that employ expansion alone.

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To evaluate the cushioning effect of casting ring liners painted with petrolatum (petrolatum painted liner) on the setting expansion of investment materials, cushioning ability was determined for 15 ceramic liners (A: rockwool type, B: ceramic fiber low temperature type, C: ceramic fiber standard type, D: ceramic fiber low temperature standard type, E: kaolin type). Petrolatum painted liners were seated inside the sliding frame of an appratus for expansion measurement, and then the setting expansion was measured for 120 min. Cushioning effect were calculated by the difference between the setting expansion with and without liner. The cushioning effect of petrolatum painted liners were classified into three groups. Group I : Painting with petrolatum improved the cushioning effect of two products of A, two products of D, one product of E. Group II: Painting with petrolatum worsened the cushioning effect of one product of C. Group III: The other nine liners slightly changed the cushioning effect.

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In this study, we investigated the strength and persistence of antibacterial activity in a resinous temporary sealing material containing silver inorganic antibacterial agent (BIKAHM-AK) on cariogenic bacteria. The disks containing BIKAHM-AK showed sufficient antibacterial activity to all bacteria tested (8 strains of 8 species) and the activity increased in a dose-dependent manner to BIKAHM-AK. The antibacterial activity was retained for at least 7 days without significant decrease even when the materials were immersed in saline. The persistence of the activity was observed in all materials containing 5〜25 wt% BIKAHM-AK. These results suggest that the resinous temporary sealing material containing BIKAHM-AK shows sufficient antibacterial activity to cariogenic bacteria and is useful for controlling plaque formation in the oral cavity after temporary sealing.

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The electrodeposition (ED) of adhesive monomer on dental alloy surface has been previously investigated to improve the adhesion of dental resin to dental alloy. In this study, the relationship between treatment conditions and bond strentgh was investigated, and the ED conditions were analyzed, using a phosphate monomer (2-methacryoyloxyethyl dihydrogen phosphate, P-1 M) The P-1 M electrodeposited on the alloy surfaces, and its phosphoric acid group formed an ionic bond on the alloy surfaces. We also found that methacrylic group was adsorbed on the alloy and its double bond existed after ED treatment. Effective treatment conditions for each alloy differed depending on the type of alloy; in a solution concentration of 1〜5% and treatment current of 0.5〜50 mA, the maximum bond strength was 8.0 MPa for 18 K gold alloy. Similary, at 1〜5%-1〜50 mA the maximun bond strength was 9.1 MPa for Au-Ag-Pd alloy, and at 5〜10%-0.5〜100 mA it was 14.1 MPa for Co-Cr alloy.

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A three dimensional finite element method was applied to calculate stress distributions of an all ceramic crown on a lower second molar under three loading conditions. When a wedge force was applied to the occlusal surface, tensile stress was produced near the fissure. As the fissure radius or the crown thickness decreased, tensile stress increased. When a vertical compressive force was applied at the fissure bottom, tensile stress was produced in the boundary surface between the crown and the abutment tooth. Tensile stress increased with a decrease in crown thickness. When a constant pressure was applied over the fissure, tensile stress was produced at both the bottom and the boundary. When the crown thickness and the fissure radius were above 1 mm and 0.5 mm respectively, the increase in tensile stress was not significant.

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Dimensional accuracy of dies obtained from agar/alginate combined impressions and vinyl polysiloxane impressions were investigated and the fit of full veneer cast crowns were also investigated. The dimensional changes of dies made of the agar/alginate combined impressions were larger at the lower portion of dies compared with the vinyl polysiloxane impressions. The difference in impression did not affect the marginal gaps of crowns, although internal gaps between the crowns and the original die were influenced by the impression. In addition, a low correlation between dimensional changes of dies and the fit of cast crowns was observed.

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A thiirane monomer with a cyclohexane ring structure, 2,3-epithiocyclohexyl methacrylate (EPCHMA), was employed as an adhesive bonding promoter for precious metal alloys. Two surface treatment agents for dental metals containing EPCHMA alone or both EPCHMA and 4-methacryloyloxyethoxycarbonylphthalic anhydride (4-META) were prepared to improve the bond strength of resin to metals. Precious and nonprecious metal alloys and pure titanium were used as an adherend. A surface treatment agent was applied to the surface of alloys polished to a mirror-like finish and allowed to stand for one day. The surfaces were washed to remove excessive monomer prior to bonding. Two alloy specimens were butt-jointed with MMA-PMMA resin and then tensile bond strengths were measured after 2,000 thermal cyclings. The surface treatment with both EPCHMA and 4-META significantly enhanced bond strengths to nonprecious metal alloys and titanium compared with the case of the treatment with EPCHMA alone, and the treatment maintained bond strengths to precious metal alloys comparable to those of the EPCHMA treatment.

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