Alginate impressions were immersed in solutions of five brands of commercially available glutaraldehyde for 10 and 30 minutes, then poured with a gypsum mix.Surface roughness, scratch resistance and waviness of the stone casts obtained from the treated impressions were measured.The effect of the glutaraldehyde depended on the immersion time.In general, immersion for 30 minutes caused deterioration in the stone cast surface.There was no adverse effect when the impression was immersed in an acidic glutaraldehyde solution without the addition of alkaline buffer.These results indicate that the buffering components(mainly phosphate)remain on the alginate impresson surface after long term immersion in the glutaraldehyde solution and this inhibits the hydration of gypsum.

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The feasibility of using various nitrides as wax pattern coating material for an Ag-Pd-Cu-Au alloy was studied. Nitrides used in this experiment were h-BN, AlN and Si₃N₄. Wax patterns were painted with the nitride coating materials, and were then outer-invested with a mixture of gypsum-bonded investment and water. The temperature of the mold was 700ºC, and the heat source was a blow pipe. Thin specimens (thickness: 0.55 mm) were cast in the 45 Ag-20 Pd-18 Cu-12 Au alloy (melting point: 930ºC) using a centrifugal casting machine. The cast specimens were investigated macroscopically and by scanning electron microscope, surface-roughness analyzer, X-ray diffractometer and micro-vickers hardness meter.
The results were summarized as follows. BN showed the benefit of separation that indicated improved cleansability and work efficiency. The BN coating layer remarkably inhibited the formation of CuO on the cast surface, only Cu₂O was detected. The color of the cast surface coated with BN was rusty red, which agreed with the color of Cu₂O. The surface-roughness (Rz) of the cast specimens decreased to less than 2/3 of the control with the use of BN. It was suggested that BN restrained the decrease in hardness of the surface layer. Nitrides did not influence interior hardness of the cast specimens.

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To monitor the biological activity of EBA and VBA, we examined their interaction with dipalmitoly phosphatidylcholine(DPPC)liposomes at various pHs using NMR spectroscopy.^1H-NMR chemical shifts of EBA and VBA in the liposome system shifted to a higher field and/or broadened at lower pH values(<pH4).VBA had a larger change in both NMR chemical shifts and DSC phase transition properties in the liposome system than EBA.

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Differences in deformation behavior around the indenter between titanium and other dental alloys were investigated using a new type of hardness tester.Dynamic hardness data, such as the relation between time and load or depth of indentation, were evaluated using a trigonal pyramid diamond indenter at a fixed load increase rate.Results obtained from this hardness tester showed good corresondence with those from the conventional Vickers hardness tester.Increments of indentation depth during load holding time depended on the alloy.In titanium, a parabolic increase caused remarkable increment within approximately twenty seconds of load holding time.Under SEM impressions indented on conventional dental alloys showed sharp accurate edges and clear slip lines around the impressions.Titanium, however, showed dull edges around the impression and there were no slip lines.These differences were associated with deformation mechanisms due to differences in the crystal structures, such as the hexagonal close-packed structure of titanium and face-centered cubic structure of other alloys.

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Pure titanium was cast into three experimental phosphate-bonded SiO_2 investment molds, a commercial MgO base investment mold and a commercial phosphate-bonded SiO_2・ZrSiO_4 investment mold at mold temperatures of room temperature and 300℃.Two different types of casting machines were used:1)a pressure type casting machine(Castmatic CM-230)and 2)a centrifugal type casting machine(Ticast Super R).The surfaces of 10×10×1.5mm cast plates were exmined.Surfaces of the plates cast in phosphate-bonded SiO_2 investment molds had a layered structure.When the mold temperature remained at room temperature, the thicknesses of the layered structure, the surface roughness and the hardness of plates cast by the centrifugal casting method were lower than those by the pressure casting method.

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The objective of this study are to determime the contact angle and the tensile bond strength of glass ionomer cement to dentin and to examine the relationships between contact angle and bond strength to dentin.Thirteen different glass ionomer cements used for luting, lining, restorative filling and base on the market were used.The contact angle and the tensile bond strength to dentin were measured according to the methods used in the previous study.The contact angle of light-cured type glass ionomer cement to human dentin showed lower value than a conventional type.The two glass ionomer cements for luting(FB and TI)were the lowest contact angles among the cements examined in this study.The cements for filling had the highest tensile bond strength to human dentin among the cements tested.The tensile bond strength of light-cured type glass ionomer cement to human dentin had higher value than a conventional type.Significant correlations between the contact angle and tensile bond strength of the cements used as lining, filling and luting were found(correlation coefficinet=-0.600, -0.865 and -0.698, respectively);however, that of the cement used for base material was not found.The results suggested that the wettability of the glass ionomer cements, excluding the cement used for base materials, to human dentin is also one of the factors predicting the bonding properties of the glass ionomer cements, as observed in the various types of luting cements in the previous study.

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This study examined the influence of various mold cavities on the reaction and mechanical properties of titanium castings.The width of the 1.5mm-thick material changed from 2.0mm to 4.0mm to 6.0mm or 8.0mm.The thickness of the 4.0mm-wide material changed from 0.5mm to 1.0mm to 1.5mm or 2.0mm.Using Titavest PS as an investing materials, test materials were cast at 600℃.The reaction of titanium castings were examined by hardness test, observation of the microstructure and Computer aided microanalyzer(CMA).Mechanical properties of titanium castings were measured using a three-point flexure test(apparent elastic modulus, 0.03% proof stress and 0.2% proof stress were calculated).From the results of the hardness test, observation of microstructure and CMA, the reaction of titanium castings increased with increases in the mold cavity.Apparent elastic modulus, 0.03% proof stress and 0.2% proof stress decreased with the increases in the mold cavity.The changes caused by increases in the mold cavity were considered to reflect decreases in the percentage of hard layer in the superficial layers of the cast materials.

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Durability of adhesion between stainless steel or acrylic resin and precious metals treated with bis(2-acrylamidoethyl)disulfide(BAEDS)was evaluated using PMMA/MMA-TBBO resin and experimental fluoropolymer/MMA-TBBO resin.Changes in tensile bond strength were tested after thermal stress cycling in water.Treatment with BAEDS containing disulfide bond was effective for gold and its alloys.However, durability against thermal stress depended on the type of adherends and resin.Adhesion of acrylic resin with PMMA/MMA resin debonded after a small number of thermocycles.

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Mold investment using a spinel investment was developed to cast full denture bases or crowns with pure titanium.The spinel investment was composed of refractory materials:magnesia, alumina and zirconia.Aluminum lactic acid was used for the mixing liquid and the liquid/powder ratio was 0.2.After firing the spinel investment at 1, 200℃, the spinel content of the mold and the remaining expansion were measured.The remaining expansion of the mold after firing at 1, 200℃ for 60min was 0.3-0.7%.However, this value was not sufficient to compensate for the titanium casting shrinkage.The remaining expansion of the mold, Y(%)was evaluated as Y=-1.52+0.074X, r=0.9(X:the spinel content, r:the coefficient of correlation).Using this investment, a reaction layer 30μm deep was formed at the surface of the titanium casting.The hardness of the layer was greater than that of the inner part of the titanium casting.The titanium-mold reaction created the hard layer in which both the aluminum and the oxygen were dissolved in the titanium.

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The present study investingated a spinel investment composed of MgO, Al₂O₃ and ZrO₂ for titanium castings.The spinel investment with added fluorides, such as MgF₂, CaF₂, had a high compressive strength and the spinel content was increased after firing.For instance, using a spinel investment containing 3% MgF₂ and 3% CaF₂, the remaining expansion was 1.2-2.5% after firing at 1, 200℃ for 60min.The compressive strength was 0.9-2kgf/mm².The remaining expansion depended on the composition of the spinel investment, firing temperature and firing time. Finally, a spinel investment with a remaining expansion equivalent to the casting shrinkage of titanium was prepared.A hard layer in which both aluminum and oxygen were dissolved in titanium, was formed at the surface of the titanium casting.However, high quality titanium castings could be cast with the spinel investment.

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The photoinitiated polymerization of(meth)acrylates(ASOE and MASOE)containing a spiro ortho ester moiety due to the combined use of benzylsulfonium salt(BSS)and photosensitizers, benzoin(Bz), benzoin ethylether(Be), benzophenone(Bp)and perylene(Pe)was examined by differential scanning calorimetry with a mercury-xenon lamp.Bz, Be and Bp were demonstrated to be photosensitizing to the photolysis of BSS at wavelengths from 297 to ca.500nm.This effect decreased in the order of Bz>Bp>Be.However, Pe inhibited the photopolymerization of ASOE and MASOE with BSS.In photosensitized polymerization, the heat from polymerization was higher for ASOE than for MASOE.Furthermore, the heat decreased in the order of full-spectra>313nm>365nm of the mercury-xenon lamp.The infrared spectral change which was a decrease of peak height at ca.1630cm^-1 and 1070cm^-1 confirmed the occurrence of polymerization of both the vinyl and supiro orthoester groups in ASOE and MASOE.

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This study examined the relationship between porosity and mechanical endurance in light-cured composite resin.Consistency depended on the shape of filler particles in the composite resin and air bubbles decreased when the consistency was lowered by a surface-active agent or heating.On statistical analysis, there was no relationship between fatigue endurance and air bubbles in the resin paste.However, there was a tendency toward increasing endurance as the air bubbles in cured composite resin decreased.

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This study evaluated new experimental soft denture liners composed of fluoropolymer(vinylidene fluoride/hexafluoropropylene copolymer)and methyl methacrylate(MMA).Liners were evaluated for water and oil sorption, hardness, water contact angle, elution of MMA and thermomechanical properties.Thermomechanical analysis(TMA)showed that the new materials were viscoelastic.The amount of MMA eluted was less than 0.02%.This value was much less than that of commonly used MMA/PMMA resins.Water sorption increased and oil sorption decreased with time.These sorption behaviors suggest the need for further research and improvement.

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The effects of sprue and air vent arrangements on the castability of pure titanium were investigated for maxillary denture frame using a suction-argon gas pressure casting machine.In general, castability increased with increases in the number of sprue.The use of one blind vent set near the palate was much more effective for making apparently complete casting than several direct vents attached to the periphery of the pattern.Argon gas pressure of 0.9kgf/cm² seemed to be sufficient in the casting machine used and an increase in the pressure to 1.4kgf/cm² induced rather adverse effects on the castability in some arrangements of the sprue and air vents.

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As a first step in developing a new polyalkenoate dental cement with superior mechanical strength and water durability, the setting characteristics of several experimental compounds were investigated by measuring the setting time.Vickers hardness, compressive strength and water durability in the lactate and borate buffer were also evaluated.The compounds were constituted by polyalkenoate solution, reinforcing inorganic fillers and calcium oxide as a reactor.Fired reactor systems containing sodium fluoride could control manipulation time and setting time of the cement.Vickers hardness of the set materials was higher than that of conventional polyalkenoate cement.The hardness of set materials using cryolite in stead of sodium fluoride was especially high.It was demonstrated that uniform distribution of fillers in the cement increased compressive strength, and water durability of set materials.The present study showed that decreasing the soluble component in set materials was important to increase the water durability of set materials.

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