Solubility and remineralization behaviors of self-setting apatite cement were investigated in organic acids of acetic, lactic, and citric acid and in synthetic saliva.The degree of supersaturation of the synthetic saliva used here was comparable to that of resting human saliva.One-week solubility of several types of self-setting appatite cement was considerably amaller than that of commercially available dental cements in the organic acids.For example, the one-week solubility of the self-setting apatite cements in citric acid, one of the most powerful acids in dissolving cements, was less than 4.5%.Thermodynamic analysis by use of chemical potential plots suggested that the solution composition was in equilibrium with dicalcium phosphate dihydrate, which probably formed on the surface.Thus no further dissolution occurred.This finding can partially account for the smaller solubility of the present cements even in the organic acids studied here.In synthetic saliva, the solution phoshphate decreased with time once the set cement was introduced to the solution, whereas the solution calcium increased.The former finding suggests that some phosphate compounds precipitated in the synthetic saliva and the latter finding indicates that some portion of the set cement dissolved.The thermodynamic analysis of the solution compositions, however, strongly suggests that remineralization is major process and dissolution a minor one.In fact, comparison of scanning electron micrographs of the cement pellets before and after the treatment in synthetic saliva showed that smaller crystals of apatite deposited on the surface of the cement pellet after the treatment in synthetic saliva.This finding comfirms that in oral environment the present cements remineralizes to take lattice nios present in oral fluids i.e.saliva, in its solid structure.

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The dimensional changes of two types of alginate impression material in air, 100% relative humidity and water were measured by means of an electronic micrometer with a non-pressure method.The effects of impression thickness, impression diameter and retentive conditions of impression with a tray were examined.The effects of three factors examined were all statistically significant as determined by an analysis of variance.The effect of impression thickness was particuraly great.The minimum impression thickness resulted in the minimum dimensional change.When the impression diameter was minimal, the contraction in air increased.A high expansion in water was observed in the absence of a tray.The number and diameter of the retentive hole in the perforated tray had little effect.These findings indicate that the alginate impression of 2.5〜5mm thickness and maximum diameter(width)ratained with a perforated tray will provide the best dimensional stability.

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The acrylic resin denture base is used more than the metal denture base, but especially upper complete denture base, it has the following weak points:The patients feel the sense of incompatibility due to a thick palatal area of denture base, and the acrylic resin denture base fails in a few years because the acrylic resin has low fatigue strength.Methods to thin the palatal area of acrylic resin denture base by reinforcement such as carbon fiber(CF)and aramid fiber(AF)cloths were developed and the static and fatigue properties of the reinforced denture bases were examined.The palatal area of CF and AF-cloth reinforced denture bases became 50% and 40% thinner, respectively.In static property, the stiffness and strength of both reinforced denture bases were somewhat improved compared to those of acrylic resin denture base alone.In fatigus property, the CF and AF-cloth reinforced denture bases were, respectively, 1.86 and 1.76 times stronger at N=10⁵ cycles.

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The cast 53Ag-30Pd-17Cu(AP), 53Ag-30Pd-17Cu-5Zn(APZ), and 70Au-10Ag-3Pd-3Pt-14Cu(Type IV)alloys were solution-treated at 700, 750, 800℃ for 3, 33, 63, 93min, softened by water quenching(Q), and then over cooled from 450 to 250℃(H).The change in their Vickers hardness(Hv)under conditions Q and H were examined.In both AP and APZ alloys, Hv after Q increased with the increase in solution treatment temperature and decrease in solution treatment time, however, Hv fluctuation due to solution treatment condition in AP and APZ alloys was ±13 and ±7, respectively, which are small values compared with those in AP and APZ subjected to H.The Hv of hardened AP and APZ increased as the solution treatment temperature increased in both AP and APZ, reaching 327 and 279 for AP and APZ, respectively, after solution treatment at 800℃ for 33min.When hardened, APZ which contains Zn had an Hv smaller than that of AP which contains no Zn, and a zinc-soluted PdCu order lattice phase was already observed after quenching.In the Type IV alloy, the changes in the solution treatment temperature and time did not give rise to the changes in Hv after Q or H.The changes in Hv after Q and H were explained based on phase transformation.

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The effect of amalgam composition and aging time on the cytotoxicity of dental amalgams was examined by means of a rapid and sensitive in vitro cell culture test.Amalgam disks(4mm dia.×1mm thick)were made at 14MPa and aged for 1 hour, 24 hours, 7 days and 30 days at 37℃.Each aged amalgam disk(n=8)was placed on a cover glass in a plastic dish.Five ml of fibroblasts, 1×10⁵par ml of Eagle's MEM with 10% fetal calf serum, were evenly seeded and incubated for 24 hour at 37℃ in a humidified atomosphere of a 5% CO₂ in air.The cover glass was removed and fixed in 10% neutral formalin and then stained by H.E.to differentiate between the areas affected or unaffected cells around the specimens.The affected area was quantitatively determined using an image analysis system.Dispersalloy(zinc-containing high-copper amalgam)showed higher cytotoxicity than any other amalgam.Lumi Alloy(high-copper amalgam)showed the same cytotoxicity as Hi-Atomic M(low-copper amalgam).Spherical-D showed the least cytotoxicity among the tested amalgams.The cytotoxicity of amalgam was decreased with aging time, probably because surface is oxidized or because the release of the elements such as zinc most responsible for the cytotoxicity, is prevented by further amalgamation.

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The plasma activated sintering method was used to make silver-samarium alloys containing 0.005〜2.0wt% of samarium.Good sintering compacts with almost 100% density were produced at the low sintering temperature of 650℃, low sintering pressure of 300kg/cm², and short sintering time of within 600 seconds.Mechanical properties of sintered compacts improved when more than 0.5wt% samarium was added.Sintered compacts were cast into the mold of cristobalite investment by the argon arccasting machine.After the heat treatment was performed at 900℃ for 30 minutes, a microstructure was observed.The microstructure of the casting specimens was equiaxed, the grain refinement effect was affected by the content of samarium, and the grain size decreased with increasing samarium content.An addition of more than 0.5wt% samarium increased the hardness but samarium was also found to be segregated by the X-ray microanalysis.The effective additive ratio of samarium on pure silver was thought to be limited to a very small amount.

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Machining properties of electric conductive ceramics with both ram and wire-type electric discharge machining were investigated to apply them to prosthetic works.All electric conductive ceramics investigated in this study could be machined efficiently with the low electric conditions by the wire-type electric discharge machine and had small clearance and surface roughness.Some of them could be machined more efficiently with the increased electric conditions.Most ceramics could be machined by the ram-type electric discharge machine with similar electric conditions to those adopted for metals.Some ceramics had a machining speed and surface roughness superior to those of pure titanium, and a prosthesis was trially made by using these ceramics.

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Studies were undertaken to apply the CAD/CAM system to Dentistry and to make prosthetic appliances automatically.The dental CAD data base was made by measuring the typical tooth models.The measurement was done by a trial 3D point digitizer.To obtain good fitness to the original figure with a small amount of surface point data, 3D spline interpolation was added.Using the convenient CAD/CAM data system, each tooth was measured at the position of the arch formation.To monitor the occlusion, the 3D coordinates and points situations enable to compile some new data, number of data, and the conditions of the interpolation, are considered.

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A compression molding machine for applying the preform compression molding method was developed.Preforms used in this study were made from polysulfone, which has excellent characteristics of high-impact resistance, high-wear resistance and high chemical stability for a denture base resin.Molding conditions, such as preform heating temperature and mold heating temperature, were examined.It was necessary to remove water in the stone cast by heating above 200℃ whenever the preform was melted on the stone cast.The pre-heated preform to the temperature of the stone cast reduced the differences in temperature between upper side and lower side of the preform by far infrared ray heater.The denture base having a thin fin less than 0.1mm was obtained under the compression molding conditions, such as heating temperature of lower mold at 290℃ and upper mold at 130℃, and pre-heating temperature of preform set on the lower mold at 290℃.

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To improve the heterogeneities of visible light-cured composite resins, acrylate-methacrylate monomers containing an acryloyl and a mathacryloyl group in a monomer were synthesized.Using UDMA as a base monomer, mechanical properties and residual carbon-carbon double bonds of acrylate-methacrylate were compared with those of dimethacrylate and diacrylate.Visible light-cured composite resins with acrylate-methacrylate had stronger mechanical properties than those of corresponding dimethacrylate, whereas unfilled resins cured by visible light had similar mechanical properties.Unfilled resin of triethylene glycol diacrylate(TriEDA)had significantly lower mechanical properties, but TriEDA gave the highest visible light-cured composite resin.The mechanical properties of visible light-cured composite resin with triethylene glycol acrylate methacrylate(TriEAMA)were comparable to those prepared by heat-cure, while the light-cured triethylene glycol dimethacrylate(TriEDMA)-composite resin had weaker mechanical properties than the heat-cured resin.The number of residual carbon-carbon double bonds in TriEAMA-unfilled resin cured by visible light was much smaller than that in TiEDMA.It is concluded that acrylate-methacrylate is useful for visible light-cured dental resins.

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The effects of pretreatment of tooth substrate for strong adhesion of resins to tooth were examined.To determine the pretreatment reagent that causes minimum damage and promotes good adhesion on tooth, diethylene triamine pentaacetic acid(DTPA)which has a chelation capacity similar to EDTA was examined.After application of 0.2M DTPA・Fe・Na-0.3M DTPA・2Na(Na salt)or 0.2M DTPA・Fe・NH₄-0.3M DTPA・2NH₄(NH₄ salt)at pH7.4, on the tooth surface, the amount of leached Ca²⁺ and the dependence of treatment time on tensile bond strength were investigated.The pretreated surfaces were also observed with SEM and TEM.Although there was no correlation between the amount of leached Ca²⁺ and the tensile bond strength, the application of these reagents had different effects on the adhesion of resin to tooth substrate.The pretreatment with either Na salt or NH₄ salt is effective for increasing bond strength of 4-META/MMA-TBB resin to dentin as well as enamel, but the bond stability on enamel is improved by the NH₄ salt.

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