Cell recovery from the cytotoxic effects of 13 commercial dental alloys of Japan and the People's Republic of China was examined in vitro using four kinds of tissue culture cells (Gin-1, HEp-2, Chang Liver, L-929). Cell recovery was observed after 7 days of incubation following treatment for 48 hours with extracts of the alloys. Cell recovery was evaluated by photo-pattern analysis and protein content (L-929). The amount of dissolved metal ions was measured by atomic absorption spectroscopy. Of the alloys examined, Cu-Al-Ni alloy yielded low cell recovery, while none of the other alloys, i.e., Ni-Cr alloys, Co-Cr alloys, Ag-Pd-Au alloys, Ag-Sn alloys, Ag-In alloys, Ti-Ni alloys and Fe-Cr-Ni alloys had an adverse effect on cell recovery. This was confirmed by measurements of metal ions in the extracts. The relationship between the results of cell recovery tests and the amount of metal ions dissolved, and the usefulness of the cell recovery test to the evaluation of cytotoxicity of biomaterials were discussed.

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Trial manufactured investments (setting expansion and thermal expansion type) and commercial phosphate-bonded investments were used for investing of disks and doughnuts types of wax patterns, which were cut by an engine lathe. K-metal was cast into these molds at a mold temperature of 700℃ by a centrifugal casting machine. Dimensional changes from wax pattern to castings were evaluated as casting accuracy. Dimensional changes in the outer diameter of the disk-type wax pattern were the same as those of the doughnut-type wax pattern. In the setting expansion type investment, the dimensional change of the outer diameter was smaller than that of the inner diameter. The thermal expansion type investment gave the opposite result. Casting accuracy correlated positively to setting expansion and negatively to thermal expansion.

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The relationship between thermal properties and powder-liquid ratio (P/L ratio) of 4products of dental cements widely used in dental clinical practice:glass ionomer cement and polycarboxylate cement, was measured and studied. The experiments were made with five P/L ratios of 0.8, 0.9, 1.0, 1.1 and 1.2 (P/L=1.0:maker's instruction) by the xenon flash method. Thermal diffusivity (×10^-2cm²s^-1) of the glass ionomer cement was 0.2119 to 0.2992 and that of the polycarboxylate cement was 0.2289 to 0.3918; it increased with the increase in the P/L ratio. The specific thermal capacity (Jg^-1K^-1) of the glass ionomer cement was 1.0723 to 1.2384 and that of the polycarboxylate cement was 0.9927 to 1.1238; it decreased with the increase in the P/L ratio. Thermal conductivity (Wm^-1K^-1) of the glass ionomer cement was 0.5052 to 0.7122 and that of the polycarboxylate cement was 0.5526 to 1.0775; it increased with the increase in the P/L ratio.

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The effects of an indium trifluoride (InF₃) incorporated in the cement powder on the physical properties of three different luting cements;zinc phosphate, polycarboxylate and glass ionomer cements, were examined. After the powder for each cement containing a small amount of InF₃ (5-7wt%) was mixed with the mixing liquid, the setting time, the compressive and tensile strengths (24hr), the film thickness, the solubility and disintegration (24hr) of each cement and the amount of F^- ions released from each cement were determined. The results were compared to those of the cements without InF₃. The mechanical properties of each cement were not affected by InF₃ with the incorporated amount used in the present study. The amount of F^- ions released from the glass ionomer or polycarboxylate cement and the F^- ions released from the zinc phosphate cement were increased in the cements containing InF₃ in the powder. The incorporation of InF₃, in the cement powder significantly influenced the setting time, film thickness and solubility and disintegration of all the cements examind.

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The purpose of this study was to evaluate physical properties of different luting cements (zinc phosphate, polycarboxylate of glass ionomer cements) containing indium trifluoride (InF₃) in the liquid. After each cement was mixed using the liquid containing approximately 100ppm F^- ions of InF₃, the setting time, compressive and tensile strengths (24hr), film thickness, solubility and disintegration (24hr) and amount of released F^- ions were determined for each cement. The results were compared to those obtained for each cement mixed in liquid without InF₃ or for each cement containing InF₃ in the powder. The addition of InF₃ to the liquid decreased the mechanical strength of the zinc phosphate cement. The amount of fluoride ions released from the zinc phosphate or the polycarboxylate cement containing InF₃ in the liquid was less than that released from the cement containing InF₃ in the powder. The addition of InF₃ to the powder for polycarboxylate cement significantly increased the solubility and disintegration. However, the addition of InF₃ to the liquid significantly decreased the solubility and disintegration. The amount of solubility and disintegration of the glass ionomer cement containing InF₃ in the liquid or the powder was greater than that of the glass ionomer without InF₃. The addition of the InF₃ to the liquid for zinc phosphate or polycarboxylate cement caused the release of a small amount of F^- ion without serious deterioration of the physical properties of the cements.

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To determine the effect of a new type of glass ionomer cement (GIC) containing a tannin fluoride preparation (HY-Agent) on dentin, the basic properties of GIC and F released from it were investigated. GIC contained 0, 1.5, 5.0, 10.0, 15.0 and 20.0 wt% of the HY-Agent in the powder. Setting time, compressive strength and disintegration were examined according to ISO. In order to determine the amount of F release, a GIC disc was immersed in distilled water for 3 months at 37℃. An increase in the amount of HY-Agent in GIC, prolonged the setting time and decreased the compressive strength. The disintegration increased markedly at a concentration of more than 10 wt%. F release was the greatest on the first day, decreasing gradually thereafter: The amount of F release increased with the increase in the HY-Agent in GIC, with a particularly marked release at a concentration of over 10 wt%. Therefore, the amount of F release may be related not only to the amount of F content of GIC but also to its disintegration.

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Sintered titanium alloys were applied to metal-cereamic restorations, and a new method of fabricating metal-ceramic crown was established. The term of powder composition, grain size, compressive yield strength, sintered shrinkage, thermal expansion and bond strength with porcelain were investigated. Bond strengths were evaluated by shear strength and bending strength with a universal testing machine and compared with those of Ni-Cr alloys. Sintered titanium alloys of 95 wt% Ti-5 wt% Al(Ti:-250〜+325 mesh, Al:16〜18μm), 80.5 wt% Ti-7.5 wt% Al-12 wt% Cu (Ti:-350 mesh, Al:16〜18μm, Cu:-350 mesh) were selected for metal-ceramic alloys because these sintered alloys had a sintered shrinkage value of less than 2%, the same compressive yield strengths as the dental gold alloys. The sintered titanium alloy (80.5 wt% Ti-7.5 wt% Al-12 wt% Cu) had the bond strength of 43 MPa with SHOFU low-fusing porcelain by bend testing. In conclusion, the sintered titanium alloy was considered applicable as metal-ceramics for clinical use.

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An adhesive metal primer (V-Primer) contains 0.5% 6-(4-vinylbenzyl-n-propyl) amino-1, 3, 5-triazine-2, 4-dithione (VTD) in acetone. Since a small amount of V-Primer is used clinically for adhesion of dental precious alloys, we examined the cytotoxicity of the V-Primer by the neutral red assay (Borenfreund, E.1985) and a millipore filter method (Wennberg, A.1979) using four experimental designs. (1) Cytotoxicity of V-Primer was compared with that of acetone using HeLa S3 cells in culture. (2) The fifty percent inhibition dose (ID_<50>) of VTD was compared with that of Bis-GMA, which was contained in a component of dental restorative resins, using HeLa S3 cells. (3 )Metabolic activation of VTD by rat liver microsomes and cofactors (S9 mix) was investigated using HeLa S3 cells. (4) Cytotoxicity of V-Primer which was applied to the metal surface was investigated by the millipore filter method. The V-Primer showed a higher cytotoxic effect than acetone. Howevre, VTD showed obviously weaker cytotoxicity than Bis-GMA, because the ID_<50> of VTD in the HeLa S3 cells was 332μg/ml, and Bis-GMA showesd an ID_<50> at 24μg/ml. Moreover, the addition of S9 mix reduced the cytotoxic effect of VTD on the HeLa S3 cells.The V-Primer applied to the metal surface showed no toxic effect on the cells by the millipore filter method. Those findings indicate that in a small amount, V-Primer may have little cytotoxic effect on human cells.

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A decrease in the sintering shrinkage of the hydroxyapatite (HAP) layer is necessary to coat HAP uniformly on the metal substrate by the sintering process, in which the HAP powder is sintered on the metal substrate via the fused glass.In this study, in order to decrease the sintering shrinkage, three kinds of binary HAP powders, which are mixtures of each coarse powder (37-53, 53-74, 74-125 μm) with the fine powder (less than 37 μm), were prepared. The coarse and fine powders were made as follows. Synthesized HAP powder containing 2.8 wt% Li₃PO₄ was fired at 1, 100℃ for 1 hour and then the product obtained was granulated with a mortar and screened. The bulk density of powder compacts for binary HAP powders was greater than that of both coarse and fine powders and the extent of the increase in bulk density increased with particle size ratio (coarse particle size/fine particle size). However, the bulk density predicted from Furnas model differed significantly from the experimental results. This difference was considerd to be due to the effects of particle size ratio and the inhomogeneity in mixing. A minimum of sintering shrinkage (8.4 vol%) was measured at the composition of 40 wt% coarse powder (74-125 μm) with 60 wt% fine powder. This shrinkage corresponded to about 1/5 of that for the normal sintering process.

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Adhesion between dentin and MMA resin was investigated using initiator systems containing 1, 3, 5-trimethyl barbituric acid (TMB) or 5-butyl-1-methyl barbituric acid (BMB), in combination with cupric acetylacetonate (CAA), and vinylbenzyltetradecyldimethylammonium chloride (VB14), cupric ion, a pretreatment solution for dentin, and an HEMA primer. CAA had the strongest effect on polymerization of MMA and the bond strength and its optional concentration was 0.0005〜0.003% in MMA. The maximum bond strength of 13〜14 MPa was obtained using MMA/PMMA resin initiated with BMB, CAA and VB14 after preteatment of dentin with-10% phosphoric acid or 10% citric acid and application of HEMA primer containing CAA. This value was comparable to that obtained with 4-META-MMA/PMMA resin using a TBBO initiator. Addition of BMB to benzoilperoxdie (BPO)/amine initiator system increased the bond strength between dentin and MMA/PMMA resin and the presence of cupric ion on the dentin surface increased the strength further. Cupric ions may be important in the interfacial initiation of polymerization of MMA in the present adhesion systems.

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Adhesion of dentin and photo-curing composite resin was studied using the photo-curing bonding agent consisting of triethyleneglycol dimethacrylate/camphorquinone/1, 3, 5-trimethyl barbituric acid (TMB). The effect of N-(2-methacryloyloxyethyl)-2-pyrrolidone (MEP) primer, cupric ion, pretreatment solution for dentin, and curing time of the bonding agent on the adhesion were investigated. A bond strength of 9.2〜10.4 MPa was obtained after pretreatment of dentin with 5% phosphcric acid and application of MEP primer, which is far geater than that usually obtained with the commercially available adhesive composite resin. Substitution of dimethylaminoethyl methacrylate (DMAEMA) for TMB in the bonding agent lowered the bond strength to 6.1〜6.8 MPa. The MEP primer was more effective than the HEMA primer in improving the bond strength and accelerating the curing of the bonding agent. Pretreatment with 5% phosphoric acid was effective in the adhesion for both dentin and enamel, and was superior to that with 40% phosphoric acid for the dentin bonding.

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An apparatus, using a small round test piece (10φ×6h, mm) screwed into a small bar was designed and produced. The apparatus was used to measure four kinds of bond strengths (by tension, shear by compression loading, flexural cleavage and torsional shear). Bond strength of two kinds of dental adhesive resins (PEX, SB C&B) to 18-8 stainless steel (SUS 304) was measured. Tensile bond strength and shear bond strength by compression loading of PEX to polished SUS 304 were 878±32, 567±84 kgf/cm² respectively, and the difference was highly significant. There was no significant difference between tensile bond strength (420±52 kgf/cm²) and shear bond strength by compression loading (405±55 kgf/cm² )of SB C&B to polished SUS 304. Bond strength by 4-point flexural cleavage of PEX and SB C&B reached over 1000 kgf/cm², and there was no significant difference between the two resins.

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Pure nickel and Ni-Cr binary alloys composed of 5〜40mass% chromium, were melted and cast to small round (10φ×4h, mm) test pieces. Tensile bond strength and shear bond strength by compression loading of two kinds of adhesive resin (PEX, SB C&B) to buff polished alloy surface and oxidized surface by heating from 200℃ to 600℃, were measured with small test pieces screwed into bars. As the chromium content increased up to 15mass%, tensile bond strength and shear bond strength by compression loading of PEX to buff polished surface increased linearly to about 500kgf/cm². Bond strength of SB C&B to the Ni-Cr binary alloys was independent of chromium content, being about 410kgf/cm², but was not improved, when an oxide film had formed on the surface by beating at 200〜600℃.

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The quantity of the remaining double bonds (RDB) in sixty-six kinds of polymerized visible ligth-cured resins was measured. As monomers, three kinds of cyclophosphazene monomers and eigth kinds of commercial monomers were prepared for the visible ligth-cured resins by changing the photoinitiator compositions (six kinds). Trial resins were investigated by means of a FT-IR with the liquid film method. The infrared absorbance measurements were made before irradiation and chronologically repeated after the resins had been polymerized by irradiation for 90sec. The quantity of RDB of all trial resins decreased linearly with the logarithmic time after the start of irradiation. When the inhibitor (BHT) was added, the order of the conversion was: 9G>BPE-200≧4G≧3G≧U-2TH>BPE-100>(EMP-800+3G)≧2.6E>(EMA)₆ > (EMA))₇₎>(EMA))₈₎. When the inhibitor was not added, the order of the conversion was: BPE-200>9G≧4G≧3G≧U-2TH>BPE-100>(EPM-800+3G)≧2.6E>(EMA))₆₎>(EMA))₇₎>(EMA))₈₎. The conversion increased with the decrease in the number of polymerization group in cyclophosphazene resins and with the increase of the CH)₂₎CH)₂₎O chain length in EDMA and BMPEPP resins. The resins with photoinitiator composition A (CQ 0.50wt%, DMAEM 1.00wt% and BHT 0.01wt%) and C (CQ 0.30wt%, DB 0.15wt%, DMAB-EMA 1.40wt% and BHT 0.01wt%) were preferable, showing high conversion. The resins not containing the inhibitor showed higher conversion than those containing the inhibitor, but had a shorter shelf life.

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The type IV gold alloy used in clinical dentistry is made by foming AuCu super lattice at around 400℃ and then aging. Solution treatment of materials of this alloy has not been studied yet although it would compose the matrix of aging material. In this experiment, to investigate the deformation behavior of solution treated type IV gold alloy, a tensile test was done and the serration mechanism which appears at the load-elongation curve was examined. The serration shape and load variation relation to temperature dependency and strain rate dependency appeared at 2.8×10^-4/sec strain rate and in the range of 0℃〜250℃ deformation temperature. Stress decrease increased with the increase in the temperature and the periodic waving of the serration became shorter with the increase in the deformation temperature then finally disappeared. In the case of constant deformation temperature and increase of strain rate, the serration form totally shifted to the low temperature side. These findings could explain the deformation behavior without any contradiction by using the P-L effect theory (Portevin-Le Chatelier effect). Another mechanism, twin deformation, was not related because line-like twining was not seen on the polished surface of the testing material after deformation by light microscopy.

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Dental alloys, such at Type IV gold and 12wt% Au-Pd-Ag alloy, are softened by heating to a temperature of 750℃ for 30min followed by quenching, and are hardened by reheating at 350℃〜450℃ for 30min. Not only the hardness of both alloys is altered by the heat hardening treatment, but also their strength and ductility are modified. The effects of heat temperature on the mechanical properties, such as tensile strength, elongation, hardness and fatigue strength of these dental alloys were examined. The Type IV gold alloys were hardened when slowly cooled or heated for 30min at 350℃〜450℃, whole its ductility decreased and its tensile strength and hardness increased. On the other hand, the 12wt% Au-Pd-Ag alloy was softened when quenched from 700℃〜750℃; the ductility increased and tensile strength and hardness were reduced. However, these alloys were hardened, when quenched from 800℃ to 850℃, but ductility was not reduced and other mechanical properties were improved. These alloys were hardened when heated for 30min at 400℃ and then its ductility decreased with the same tensile strength and hardness as those at 800℃. Hence, 12wt% Au-Pd-Ag alloys had 1.8 times greater fatigue strength at 800℃ than at 400℃. Furthermore, its fatigue properties became similar to those of gold alloys. This is probably due to the fact that the ductility of the alloy increased and its tensile strength improved.

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To obtain basic information for improvement of the corrosion-resistant nature of dental Ag-Pd-Cu-Au alloy, its corrosion behavior, such as the electrochemical chage, surface structure change, corrosion product, and ion-release rate in a dielectric solution, was investigated. The rest-potential of the dental Ag-Pd-Cu-Au alloy was high in 1% NaCl and 1% C₃H₆O₃ solutions and low in artificial and human salivas. The corrosion rate, which was measured by anodic polarization, was fastest in the 1% NaCl solution, followed by artificial saliva and 1% C₃H₆O₃ solution. The rate was slowest in human saliva. An aged specimen and an as-casted specimen were quickly corroded. The AgCl was produced at the specimen surface in the 1% NaCl solution as well as the artificial and human salivas during the polarization measurement. Ninety percent of the ions released from the as-casted specimen immersed in the human saliva was Cu. The amount of ion release of Cu and Ag in the human saliva strongly depended on the heat treatment. The amount of Cu and Ag ions released in the human saliva decreased with an increase in immersion time. Fine, needle-like crystals of HAp covered the surface of the speciment immersed it the human salive and the calf serum.

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In this study titanium copings were fabricated using the CAD/CAM process and their clinical application was studied. The lower 1st molar was prepared for the full coverage crown with shoulder. The impression was taken using silicon rubber impression materials and a stone die was prepared. The stone die was digitized by the laser digitizer and the data was collected, treated and reconstructed on the personal computer as the computer graphics. The design of the coping was carried out on computer (CAD) and the numerical program for the machining was prepared. The CAM process of the coping was carried out using the NC wire type electric discharge machining, NC milling and NC laser welding. The final crown was completed by covering the titanium coping with composite resins. In this system the digitizing and CAD process could be carried out in a short time. The CAM process could guarantee high precision even for a titanium copings. This system was found to be practical because the laboratory process could be eliminated and the new technology could be combined with conventional laboratory techniques.

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