It is known that metallic glass alloy, so-called amorphous metal, is produced by quench-casting at a rate one million degree per second.The purpose of the work described here is to evaluate the possibility of the amorphous brazing filler metals for dental use.The strength characteristics of joints made with two different kinds of nickel base amorphous filler metals were compared with those of the joints made with traditional gold alloy solder.Co-Cr and Ni-Cr alloys for dental cast were adopted as the base metals.Tensile, impact, hardness and tarnish test were caried out.The results obtained were as follows:(1)Though the joints were brazed in air, their mechanical properties were comparable to those of joints brazed with gold alloy.The joint strength was excellent when the basic composition of the filler metal was similar to that of the base metal.(2)In the tarnish test it was found that the ioints had satisfactory resistance to corrosion.(3)The filler metals in foil form were convenient to control their amounts and to ensure appropriate space between the base metals to be brazed.(4)In order to avoid a porous brazed joint, brazing should be done by using the highest possible temperature flame in the shortest possible time.For this reason the holder was effective than investing.(5)The excellent flow characteristics of the filler metals made it possible to fill gaps of up to 0.03mm.(6)The color of the filler metal matched that of Co-Cr or Ni-Cr alloy system to be brazed.

View full abstract

The relationship between the dimensional change and the marginal leakage of dental amalgam was investigated. In order to vary the dimensional change in a wide range, amalgam alloy and mercury were mechanically triturated either for 5, 10, 15, 20, 25 or 30 seconds.A single mix was used to evaluate both the marginal leakage and the dimensional change.The marginal leakage was evaluated by means of the depth of dye penetration and the dimensional change was measured for 24hours using an electric micrometer. Both experiments were repeated three times for each trituation time employing a lathe-cut alloy and a spherical alloy.The results are summarized as follows.The marginal leakage of the amalgam restorations significantly correlates to the dimensional change at 24hours after the trituration.The relationship between the depth of dye penetration, D(mm)and the dimensional change at 24hours, C(μm/mm)is given by the following regression equations. D=0.0036C²-0.101C+0.71 for the lathe-cut amalgam D=-0.054C-0.54 for the spherical amalgam

View full abstract

Fe, In and/or Sn were added to 88Au precious alloy and 15kinds of alloys were prepared.Total concetration of the additional elements was 1wt%.Two specimens for thermal expansion measurements were cast separately from each alloy, and thermal expansion(%)and thermal expansion coefficient were determined.Maximum temperature of the measurement was 970℃.Thermal expansion coefficient was determined within 200℃ temperature range(room temperature〜200℃, 200〜400℃, 400〜600℃, 600〜800℃ and 800〜970℃)by linear regression.Below 800℃, it did not depend on the content of additional elements.Average coefficient values of this alloy system are;12.9×10^-6/℃(RT〜200℃), 14.6(200〜400℃), 15.6(400〜600℃)and 17.3(600〜800℃).In the range of 800〜970℃, the coefficient strongly depended on In or Sn content, especially during the first cycle heating period.Contrasting other methods of determining thermal expansion coefficient, it was concluded that our method was the most convenient and reasonable to compare the thermal expansion coefficient of alloys and porcelains.

View full abstract

The effect of fluoride content in apatites as a filler of dental composite resins on their mechanical properties was studied.Fluoridated hydroxyapatites were synthesized at 80℃ and at pH 7.4, and mixed with 2・2′-bis(4-methacryloxyethoxy phenyl)-propane.The compressive strength and Knoop hardness of the composites did not change significantly with the degree of fluoridation.In tooth cavities, the composites seemed to adhere well to enamel without a bonding agent, and any microleakage was not found.The adhesive strength of the composites was also scarcely affected by the fluoride content.

View full abstract

The changes in phase transition temperature(Tm), enthalpy(ΔH), H/HHW(height/half-height width)value of dimyristoy land dipalmitoyl phosphatidyl choline(DMPC, DPPC)liposomes induced by phenyl-P, HEMA, 4-META, MMA, TEDMA, Bis-GMA, Iso-Bis-GMA were studied by differential scanning calorimetry(DSC), in order to clarify the mechanism of phospholipid interaction with monomers in bonding agents.Phospholipid interactions with these monomers were examined by ¹H-NMR spectroscopy.It is suggested that the changes in the Tm, ΔH, H/HHW values may not only be due to the hydrophobic interaction, but also due to the double bonds or the functional groups(amino, hydroxy, phosphate, etc.)in monomers.The profiles of these adhesive monomers using DPPC liposomes were characterized by shift in Tm usually to a lower temperature and a decrease in ΔH with a reduced H/HHW value.Iso-Bis-GMA changed transition behavior more singnificantly than Bis-GMA.

View full abstract

Casting properties of a 18-8 stainless steel as a cast denture alloy were studied.The steel and a Co-Cr alloy were cast into phosphate-bonded investment molds by use of an argon high-frequency pressure casting machine.Proof stress of the steel was fairly lower than that of the Co-Cr alloy, indicating that the application of the steel was limited to full denture.Ultimate tensile strength of the steel was nearly equal to that of the Co-Cr alloy.Elongation of the steel was larger than that ot the Co-Cr alloy.Corrosion-resistance and castability of the steel were sufficient for cast denture.The surface of the steel castings was rough for reaction with molds.Casting accuracy of the steel was nearly equal to that of the Co-Cr alloy.

View full abstract

Permeadility of eight dental casting investments was measured at high temperature by the equipment described in the second report.Also thermal expansion, which is essential to the production of correct dental castings, was measured by thermal mechanical analizer(TMA).In this report, the correlation between permeability and thermal expansion was investigated.The obtained results were as follows:(1)Permeability correlated to expansion during the heating.(2)Higher powder-liquid(water)ratios gave higher permeadility values.(3)Phosphate-bonded investments had little permeability in heating up to 200℃.(4)The colloidal silica mixes of investments and the addition of carbon to investments increased permeability.

View full abstract

Recently, non precious alloy is commonly used for dental treatment instead of precious alloy.But only a few studies were reported about its electrochemical behavior.The purpose of this study was the basic research for the study of application of electrolytic polishing and elctrolytic etching to Cr-Co-casting(Cr was contained 0〜50%)and Cr-Ni casting(Cr was contained 0〜20%).The relation between potential-current density curve(V-A urve)and potential sweep rate was observed, they were concerned each other, then reproducible and efficent potential sweep rate was considered 35mV/min.The ralation between V-A curve and electrolytic conditions(those were, the distance between electrodes, the area of positive electrode, concentration and temperature of phosphoric acid)and as cast or annealed metal.Findings were as follows 1.V-A curve was closely related to content of chromium.Less than 10% Cr, the value of electrolytic etching was higher, so this indicated in reference to corrosion resistance.2.Electrolytic coditions influenced V-A curves.a)Distance between electrodes(10〜40mm)had a little influence with V-A curve.b)According as area of positive electrode incresed, density of current became smaller, but potential of remarkable point did not change.c)Concentration and temperature of phosporic acid produced remarkably effect on V-A curve.3.Annealing(900℃ 1 hour)was considered no effect on electrolytic behavior.4.The value of decrease by electrolytic treatment under constant current density was in propotion to time of electrolytic treatment.

View full abstract

Recently, dental abhesive resins have been clinically applicable, but more superior adhesive resins are desirable.In this study, we synthesized 6-methacryloxyethyl naphthalene-1, 2, 6-tricarboxylate anhydride(MENTA-126)as one of the methacrylate monomers having both of hydrophillic and hydrophobic groups, and investgated adhesion to tooth of the self-curing methacrylic resin containing of MENTA-126.The results that adhesion of the MENTA-126 resin to tooth had high strength and good stability, clearly showed the prominent adhesion ability of MENTA-126 to tooth.Adhesive strength of the MENTA-126 resin had approximately equal magnitude of the resin containing of 4-methacryloxyethyl trimellitate anhydride(4-META), which have a simular molecular structure to MENTA-126.Therefore, also by us, the effectiveness of the monomer having both hydrophillic and hydrophobic groups on adhesion to tooth was suggested.

View full abstract

The tarnish test, the wear test and the bending test of TiN Ion-plated specimens for various alloys were performed.Results(1)The TiN film had the colorimetric properties which were the hue of about 2.5Y, the value of about 6 and the chroma of about 4 by the standard color chip of JIS.(2)The resistance to tarnish of alloys was improved by Ion-plating.(3)The wear of TiN film didn't depend on mechanical properties of the base(substrate)material if the maximum depth under the wear test was less than Ion-plated film thickness.(4)Wear amounts of TiN film were large to inorganic materials such as TiN film porcelain and enamel but small to metallic materials such as Type IV gold alloy and Ni-Cr alloy.(5)Wear amounts of Ag-In alloy and porcelain were large, but those of Type IV gold alloy, Ni-Cr alloy and enamel were relatively small to TiN film.(6)The composite materials which TiN films of 3μm thickness were plated on both sides of 0.3mm thickness-substrate(Ag-Cu alloy)gave 20 percent increase in the elastic coefficient and 50% increase in the proof stress under the bending test.

View full abstract

We have been studying adhesives to tooth substrates and the adhesion mechanism.It was found that phosphoric acid etching demineralized the dentin and the denaturation of collagen was also taken place during the etching.A weakened surface layer on dentin where adhesives were applied was formed due to the reaction.Dentinal plugs were also dissolved away by the acid.Affection of zinc phosphate cement on dentin during the setting of prosthetics was expected to be the same as the acid etching prior adhesion.Dentin surfaces modified by a zinc phosphate cement were observed by SEM after removal of the cement at several intervals.The observation was also carried out on the dentin treated with the liquid in the cement.The tensile adhesive strength to the dentin treated with the cement which was washed out was lower than that to the dentin etched with the acid.The glue was 4-META/MMA-TBB resin.The anticipation was confirmed through the experiments written above.Chemical modification of dentinal collage with glutaraldehyde could minimize the adverse effect of the cement on dentin during the cementation.

View full abstract

This study was planned to investigate usability of bovine teeth as substitute for human teeth in the bonding test.Tensile adhesion of adhesive restorative materials to their enamel and dentin was determined.Ca content of the tooth specimens was also determined by using an electron probe microanalyzer.Findings were as follows:1.The adhesion to enamel and superficial dentin layer was comparable between human and bovine teeth with no statistically significant difference.2.Although the adhesion of the adhesive resin to enamel was great, it did not necessarily follow that great adhesion to dentin was obtained, in the individual human teeth.In bovine teeth, the great adhesion was more or less shown in enamel and dentin.3.A significant correlation was found between Ca content of the tooth substances and bond strength of resin to tooth.4.For the bonding test of various restorative materials, the first and second incisors of matured bovine having over 40mm tooth length are satisfactory substitutes for human teeth as adherend.

View full abstract

In the irradiation of laser to teeth, cracks are introduced on enamel surface and the temperature in pulp chamber is elevated.These behaviors are considered to be damageable to teeth. Safe energy density of laser exposure to teeth was found to be below 24J/cm².Acid solubilities of enamel blocks were tested for a) unlased samples, b) only lased, c) unlased, treated with caries inhibiting agents(38% Ag(NH₃)₂F, 2% NaF, 8% SnF₂, 2% FeCl₃+1% NaF), and d)lased, with the previous treatments.Laser irradiation tended to decrease their acid solubilities.The X-ray diffraction analysis of lased enamel powder showed that the crystallite size of enamel apatite increased in the a-axis and decreased in the c-axis.Acid solubility of lased enamel decreased as the specific surface area of enamel apatite calculated from the crystallite size decreased.

View full abstract

Decomposition product of hydroxyapatite irradiated by CO₂ laser with energy of 300〜24000J/cm²was examined by X-ray powder diffraction method.In the X-ray diffraction patterns a few peaks of α-and β-tricalcium phosphate were observed at 800J/cm².The products lased with 3200〜24000J/cm² were composed of 75wt% hydroxyapatite, 21wt% α-, and 4wt% β-tricalcium phosphate.The lased product and hydroxyapatite powder heated at 500〜1300℃ were incubated at 37℃ in pH 7.4 Tris-HCl buffer.Ca concentration of these solutions were measured.The solubility of lased product with 24000J/cm² was found to be 3 to 5 times as large as that of hydroxyapatite.The product lased with 24000J/cm² and hydroxyapatite powder heated at 700℃ were injected into tibia of Whister rats.The animals were sacrificed at 1, 2, 3, 4, and 5 weeks and investigated histrogically.New bone tissues were grown around the lased products as well as hydroxyapatite.

View full abstract

The purpose of the present study was to develop the apparatus in order to examine the marginal strength of the restorations.Approximately three fourths of the restorations in posterior teeth are of silver amalgam, but the composite resin is growing popular gradually and it will be wide-spread in near future.Since the amalgam is brittle as well known, the set amalgam does tend to fracture at the margin.The composite resin which was applied to the posterior teeth would also show the marginal fracture to a certain extent.Although Jφrgensen, Mahler, Osborne, and others studied on the marginal fracture of amalgam and it was postulated that creep was in some way associated with the marginal fracture of amalgam restorations, little has been reported on its cause and progress.Therefore, the authors developed the apparatus moves the specimen horizontally under the constant load of steel sphere and controls the moving speed of the specimen.It automatically records the location of the specimen, the vertical displacement of the steel sphere on the specimen and the exact position of the end of the specimen.By this apparatus can be observed the initial and final fractures of the specimen.The DEPTH and WIDTH on the marginal fracture as well as the vertical displacement data were calculated by the microcomputer with digitizer.The values were compared with the picture of the fractured specimen.

View full abstract

Sufficient bond strength of the brackets to the tooth surfaces in the course of active treatment and the adhesion characteristics which facilitate the removal of the brackets from the tooth surfaces in the last treatment phase have been one of the essential requirements in orthodontics.The purpose of this study is to develop such adhesion system.In the present study, thermal property a sa adhesion factor was adopted in order to investigate the effects on the adhesion between brackets and tooth surfaces.Orthodontic metal brackets were directly bonded to extracted human teeth with three orthodontic adhesives(Super-Bond, Concise and System 1).The bond strength were measured at 30℃, 70℃, 90℃ and 150℃ in a simple small electric furnace.All the adhesives had a tendency that their tensile and shearing strength decreased with the increase of temperature.The tensile strength of Super-Bond and Concise showed their maximum values at 30℃.Super-Bond lost almost its bond strength at 90℃.Concise decreased gradually its bond strength and even at 150℃ it maintained still low value.Similar tendency was observed for System 1 at higher temperature when compared with Concise.The pattern of the shearing strength in each adhesive with the increasing temperature was also analogous to that of its tensile strength.

View full abstract

In order to investigate the effect of physical properties of alloys and investments at high temperature on the casting shrinkage, the casting shrinkage of cylindric castings were measured.In addition, the physical properties of materials(the coefficient of thermal expansion, the coefficient of elasticity and yield point)were measured at high temperature;and the thermal stress and shrinkage were numerically analized.With the results of measurement, on the alloy that has no phase transformation such as Au-4.0wt% Cu alloy or α-brass, the casting shrinkage was as much as free shrinkage;but on the alloy that has phase transformation such as Au-25.0wt% Cu alloy or β-brass, the shrinkage was lessen.Furthermore the result of neumerical analysis used measured physical properties showed that the investment such as cristobalite, that expansion remains at low temperature during the cooling stage, restricts the shrinkage of alloy such as β-brass that has a low yield point at high temperature.

View full abstract