Specimens prepared with three commercial dental amalgams were immersed in three kinds of solutions:Ringer's, 1% lactic acid and 0.05% hydrochloric acid, at 37℃, and subjected to a repeated corrosion test for fifteen weeks.Quantitative analysis was performed by inductively coupled plasma emission spectrometry for released metal elements to determine the composition of these amalgam alloy powders and immersed specimens.The immersion test for one week was not sufficient to prove the corrosion tendency of amalgam and a longer period of immersion was considered necessary.The kinds and amounts of released elements in each solution differed, and the corrosion tendency of high copper amalgam differed from that of conventional amalgam.

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The tensile bond strength of new bonding agents on human dentin treated with 37% phosphoric acid solution for 60 sec to a photocurable compostite resin was measured and the fractured surface was then observed by SEM.The new bonding agents consisted of various 20wt% high molecular monomers(MW.1500, 5000, urethane acrylate oligomer)as a base monomer.The best bonding agent was a mixture of 20wt% 1500 molecular monomer as a base monomer and the value of the tensile bond strength was 91±17kgf/cm².The tensile bond test and SEM image of the fracture surface suggested that a high molecular monomer as a base monomer promoted the adhesive efficiency to human dentin.

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Studies are currently underway to apply the CAD/CAM system to dentistry and to make prosthetic appliances automatically.This paper reports the basic CAD procedure by using the CAD data base in the previous(part 3)report and gives some modified teeth figures.Mathematically, with Affine transformation, extention, contraction, parallel translation, and rotation of the dental figures are done.In the transformation, the origin of the individual tooth is decided from the mean value of the data base points, and X, Y, Z coordinates are the bucco-lingal, mesio-distal, vertical directions, respectively.This basic transforming procedure reduces the time needed for the CAD procedure.

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An adhesion promoting monomer of 3-methacryloyloxybenzoic acid(3-MBA)was utilized as an ingredient of experimental dental photocurable bonding resins.Effects of the monomer compositions of the resins on the bond strength to tooth substrates were examined.The bond strength of the light-cured resin was enhanced by the addition of 3-MBA.When 3-MBA was incorporated with Bis-MPEPP_2.6E, TEGDMA or their binary comonomers, the bond strengths obtained were ca.130kgf/cm² for the enamel treated with an aqueous solution 10% citric acid and 3% FeCl₃ and ca.50kgf/cm² for the dentin.SEM examination revealed that the acid resistant dentin layer was formed by the infiltration and polymerization in situ of the monomer of the 3-MBA bonding resin.However, bond strengths of less than 50kgf/cm² obtained on treated dentin could be explained by the extent of the tag formation in dentinal tubules.

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We evaluated the use of aqueous solutions containing an acid and metal chloride as a tooth surface pretreating agent.Nineteen solutions containing 10% acetic(AA), citric(CA), lactic(LA)or phosphoric acid(PA)and/or 0.11M aluminum(Al), cupric(Cu)or ferric chloride(Fe)were prepared.The tensile bond strengths of the TBB-O initiated MENTA resin to tooth surfaces treated with the respective aqueous solutions were measured.The amount of dissolved Ca by each of the solutions was determined.The demineralization of tooth surface was mainly dependent on the pH of the aqueous solutions.There was no specific relationship between the bond strength and amount of dissolved Ca.This suggests that a high bond strength can be obtained without serious demineralization.Pretreatment with the CA-Cu, CA-Fe or LA-Cu solution markedly enhanced the bond strengths to both enamel and dentin, altough these solutionsdemineralized tooth surface less than the solutions containing 10% PA.

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Twelve kinds of Ag-Pd-Cu alloy, containing 25, 30, 35, 40wt% Pd, 20, 25, 30wt% Cu and the residual quantity 30〜55wt% Ag were melted in an argon atmosphere.These alloys were cast using dental precision casting, subsequently, softening heat treatment(water quenching from 800℃)and hardening heat treatment(450→250℃ oven cooling)were applied.After softening heat treatment, the Vickers hardness, tensile strength, and elongation of the experimental alloys ranged from 145 to 200, from 41 to 60kgf/mm² and from 11 to 27%, respectively.Therefore, these alloys were very ductile in softening heat treatment condition.After hardening heat treatment, the Vickers hardness of the alloys increased in the range of 241〜433 and tensile strength in the range of 73〜107kgf/mm².However, elongation decreased to 0.5〜3.5%.Composition of the alloy that had the maximum tensile strength(104kgf/mm²)was about 45Ag-35Pd-20Cu.Brightness(L^*)of the test pieces that were immersed in 0.1% sodium sulfide solution of 37℃ for 3 days ranged from 58 to 67.After hardening heat treatment, the Ag-Pd-Cu ternary alloy containing 20〜30% Cu, 30〜40% Pd had satisfactory high hardness and strength for adhesion bridge, but their elongation and tarnishing resistance were insufficient for clinical application.

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Nine experimental Ag-Pd-Cu ternary alloys, containing 20〜30wt% Pd and 10〜20wt% Cu, were cast into rods 4.5mm in diameter using an original vacuum/argon-pressure oxide-free casting technique.Test samples 2.0mm in diameter were made from the rods by wire-drawing.After softening and herdening heat treatments, mechanical properties(modulus of elasticity, elastic limit, proof stress, tensile strength, elongation, and Vickers hardness)of the samples were measured to analyze the effects of composition and fifteen sets of correlations between the mechanical properties on the condition that few internal casting defects existed.After softening heat treatment, values of hardness and strength increased with increasing Cu and Pd contents, while they increased approximately with increasing Pd content after hardening heat treatment.After softening and hardening heat treatments, tensile strength ranged from 44.4 to 60.7 and from 68.1 to 89.1kgf/mm², respectively.Values of elongation were more than 10% even after hardening heat treatment.Fourteen out of fifteen correlation coefficients(r)were statistically significant(p<0.01).One of the regression lines derived was as follows.Tensile strength(kgf/mm²)=9.1+0.305Hv(r=0.990)Moreover, the mechanical properties observed in this investigation were compared with those of ordinarily cast samples with the same compositions.

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Addition of barium hydroxyapatite(BaAp)successfully bestowed clinically acceptable radioopacity to the self-setting apatite cement consisting of an equimolar mixture of tetracalcium phosphate and dicalcium phosphate dihydrate.To accelerate the setting reaction which was retarded by Ba²⁺ released from BaAp at a lower pH during first stage of spatulation with 20mM phosphoric acid, calcium hydroxyapatite(CaAp)was added to the cement mixture.At about 20wt% of BaAp and 20wt% CaAp, the setting reaction proceeded at a neutral or weak alkaline pH, which is one of the most promising aspects of the self-setting cement and assures that this type of cement may be the least irritating of the dental cements presently available.The cement spatulated at L/P=0.4 set within 10 minutes and its radiopacity was comparable to or more than that of tooth enamel.The wet compressive strength of the set cement stored for one day in synthetic saliva at 37℃ was approximately 100kgf/cm².Although this value is almost one fourth that of 40wt% CaAp cement, this cement appears to be strong enough to apply as root canal filling material.

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The reactivity of various refractory oxides(SiO₂, Al₂O₃, MgO, CaO, ZrO₂)with molten titanium was investigated by energy dispersive X-ray spectroscopy(EDS), using single crystals of oxide as specimen.The region of the reaction boundary between titanium and single crystal oxide was observed by electron microscopy(SEM).Elemental analysis across the Ti/oxide boundary was done by EDS and the reaction layer thickness was quantitatively determined.Of these refractory oxides, SiO₂ is the most reactive with titanium followed by Al₂O₃.The 250μm thick Si-rich region and 100μm thick Al-rich region were formed respectively in Ti around the remnant oxides.The diffusion of Si as a result of reaction is greater than that of Al.MgO, CaO, ZrO₂ show very little reaction with Ti and the reaction layer thickness was below the spatial resolution of EDS(approximately 1μm).The thickness and composition of the reaction layer and reactivity were determined.These results were in good agreement with those obtained by ESCA.

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A preform compression molding method to make polysulfone denture was reported previously by paper.Properties of the mold, adaptability of the molded denture to master model and the movement of artificial teeth were examined.It was necessary to raise the temperature of the crystbalite-stone model above 270℃ to obtain stable expansion.Mold made using 22wt%-colloidal silica showed strong compressive strength under the compression molding condition.Displacement of artificial teeth between wax denture and polysulfone denture was independent of the mold expansion, and the displacement was equal to that of heat-curing acrylic denture.Adaptability of the molded denture to the master model was associated with expansion of the model.Good adaptability was obtained under the expansion of the model, such as setting expansion about 0.30% and total expansion 1.05-1.10%, with about 0.2mm average discrepancy.

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Titanium was polished using several chemical polishing baths containing different ratios of hydrofluoric acid and nitric acid.The meltage, surface roughness, and surface texture of titanium samples after chemical polishing were affected by the ratio of hydrofluoric acid and nitric acid.Generally the meltage increased and surface roughness decreased when the mole concentration of hydrofluoric acid was high and that of nitric acid was low.For example the chemical polishing bath containing 5 mole hydrofluoric acid and 5 mole nitric acid improved the surface texture in one minute, but SEM observation revealed a partially rough surface caused by the excessive solution The chemical polishing bath containing 1 mole hydrofluoric acid and 5 mole nitric acid did not improve the surface texture in a short time because of low solubility, but improved the surface texture gradually with the extension of the immersion time and a good surface texture was observed by SEM.The chemical polishing using the chemical polishing bath with low solubility and immersion of the prosthetics for a rather long time were considered useful procedures to obtain a smooth surface of titanium prosthetics while maintaining their accuracy.

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The effect alkyl ammonium salt/Sn composite plating on the adhesive characteristics of dental alloys was examined.The surface of dental alloys, on which such a composite plating was made, was analyzed by ESCA.The effect of the length of alkyl chain and its terminal atomic groups on the tensile adhesive strength to an adhesive resin was also examined.ESCA analysis revealed that both C and N atoms from the alkyl ammonium salts were certified on the surface of the dental alloys.Stable tensile adhesive strength, as high as 500kg/cm², was obtained when the number of C atoms of alkyl chain was 10 to 16.The alkyl ammonium salts containing such groups as hydroxyl, amino and vinyl at the terminal of the alkyl chain, were effective for increasing the tensile adhesive strength.

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