Mechanical properties of heat curing acrylic resin obtained by polymerization for long period of heating at a temperature lower than conventional temperatures were examined.The mechanical properties of the resin were lower than those of the resin cured at 100℃.The results of high performance liquid chromatography and differential scanning calorimetry suggested that the poor mechanical properties were due to significant amounts of residue monomer and benzoyl peroxide in the resin, but is not to changes molecular weight.

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To improve the transmittance of light-cured composite resins, the matching of the refractive indices of the matrix monomer and filler were examined.Eight fluorinated aromatic dimethacrylates and diacrylates with a low refractive index were synthesized.Three of these monomers had a poor solubility to TEGDMA.The depths of cure and the other physical properties of eight experimental composites prepared from one of five fluorinated monomers, TEGDMA and UDMA were determined compared with those of the control composites prepared from Bis-GMA or Bis-MEPP/and TEGDMA in the same ratio.These composites contained 70wt% of silanized silica filler.The depths of cure of the experimental composites except for one were significantly greater than those of the control composites.The mechanical properties of the experimental composites were comparable to those of the control composites with a few exceptions, but the difference in the mechanical properties between these exceptional composites and the control was small.The water sorption of the experimental composites was markedly lower than that of the composite containing Bis-GMA and comparable to that of the composite containing Bis-MEPP.These five fluorinated monomers are considered useful as the matrix monomer of light-cured composite resins.

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The goal of this study was to test the influence of the type and oxidation treatment of dental casting alloys on the tensile bond strength of luting cements.Also, the influence of film thickness of luting cements on the tensile bond strength of different dental casting alloys was examined.Four different luting cements(zinc phosphate, polycarboxylate, glass ionomer and adhesive resin cements)and four different dental casting alloys(Au-Ag-Cu, Ag-Pd, hardened Ag-Pd and Ni-Cr alloys)were used.Cylindrical alloy rods for the tensile bond strength test were casted, and then, top surfaces of the rods were cemented with each luting cement to the bottom surfaces of other rods, using the film thickness adjustment apparatus.The film thickness of luting cement was adjusted to 20, 30, 50, 75 or 100μm.The tensile bond strengths of each cement to different casting alloys at each film thickness were measured one day after the rods had been cemented.The tensile bond strength of the zinc phosphate cement could not be determined in this study due to the separation of the alloy rods cemented with the zinc phosphate cement in water before the tensile test.The tensile bond strength of the adhesive resin cement to any alloy showed the greatest strength;however, that of the glass ionomer cement to any alloy was the lowest strength among the cements examined.The Ni-Cr alloy had the highest bond strength of any luting cement, compared to other alloys.The tensile bond strengths of luting cements significantly decreased with the increase in film thickness of cement layer.The adhesive resin cement had the greatest bond strength, and the glass ionomer cement was the lowest bond strength at any film thickness.The oxidation treatment significantly increased the bond strength of the adhesive resin cement to both Au-Ag-Cu and Ag-Pd alloys.The tensile bond strength of the adhesive resin cement was most dependent upon the film thickness of cement layer, and that of the polycarboxylate cement was least dependent upon the film thickness of cement layer among the cements examined.In addition, the oxidation treatment for precious alloys could be a factor contributing to the increase in the bond strength of the adhesive resin cement.

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A preliminary CAD system to design the inner and outer shape of crown prostesis was developed using the data of 7 abutment and molar measured in the previous paper.The gingival and marginal line in the abutment tooth could be recognized more certainly by the"GIN-MAGN"program, and the three dimensional data of tooth crown above the gingival line could be output and saved.To prepare the data base of the occusal surface of tooth crown, the data of tooth crown above the gingival line of 7 molar were also output by the"GIN-M"program.The data around the toothneck were excluded with an arbitrary height above the gingival line in order to connect smoothly with the margin line of the abutment tooth.The tooth crown data were set up on the abutment data by means of the program"AB-CR-E".In the present system, even though the occusal condition with the antagonistic tooth could not be taken into account, the CAD procedure to set up a tooth crown with an arbitrary size on the arbitrary position of abutment tooth could be accomplished, and the toothneck data of crown were connected with the margin of abutment tooth.

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A new time-saving method has been developed to produce artifical crowns without using the casting process.Plastic mixtures of gallium and other metal particles are kneaded into desired shape and then heated for hardening.By this method, the time required for hardening and producing restorative materials has been shortened greatly.In the present experiment, gallium was triturated with powdered gold, silver and copper to make binary alloy samples.The dimensional change was measured between heat treatment.After heat treatment, the test piece was examined for compressive strength, compressive shrinkage, hardness, tarnishing and difference in phase.Non-heated and heated alloy specimens(Au-Ga, Ag-Ga, Cu-Ga)expanded to form the new phase.The ability of Au-Ga samples to bear compressive strength, when heated at 300℃ or more(AuGa₂→AuGa), became 2.6 times greater than that of non-heat-treated specimens.The compressive strength of Ag-Ga samples dropped briefly at 350℃(Ag_0.72Ga_0.28→Ag₃Ga)but increased at 450℃(Ag₃Ga→AgGa).The strength of Cu-Ga pieces fell by half at 475℃ and upward(CuGa₂→unknown phase).A compression test showed that the contraction percentage of Au and Ag specimens became large as a result of heat treatment, while that of Cu alloys remained almost unchanged.The results of a hardness test(HV)were comparable to those of the compressive strength test.The Au-Ga alloys increased in hardness after high-temperature treatment.In the Ag-Ga alloys, hardness declined at 350℃ and increased at 450℃.There was no difference in hardness between Cu specimens after heat treatment and those allowed to stand at room temperature.A tarnishing test revealed that Au-Ga samples turned slightly yellowish.In the case of Ag-Ga samples, the reflectivity Y(%)dipped slightly but discoloration was not recognizable.However, the Cu-Ga samples which were heated at temperatures of up to 280℃ showed a slight drop in reflectivity, but those heated at temperatures higher than 280℃ decreased to 50〜66% in reflectivity and turned black.

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Ag-Pd binary alloys with various palladium contents were extracted in Eagle's minimum essential medium by dynamic extraction at 200rpm at 37℃.The extracts were filtered through a 0.22μm cellulose acetate filter, and the silver and palladium amount of the extracts and filtrates as dissolved metallic elements was measured with atomic absorption spectroscopy.Extracts and filtrates were also used in cultivation of L-929 cells to study in vitro cytotoxicity.An increase in the palladium content of the alloy resulted in decreased silver dissolution and increased palladium dissolution.The amount of palladium in the filtrates increased as the extraction period was extended, but the amount of silver was negligible in all filtrates.Extracts which had been extracted for 1day showed strong cytotoxicity in pure Ag.However, the addition of palladium at a weight percent of more than 40% decreased cytotoxicity almost to the control level.Filtrate which had been extracted for 1 or 3 days was noncytotoxic in all alloys.However, the filtrate which had been extracted for 5 or 7 days showed cytotoxicity, which was especially strong in high-palladium alloys.These results demonstrate that extraction using a dynamic method appears to be useful in the investigation of their corrosion and biocompatibility.

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Adhesion durability between dentin pretreated with 10-3 and 4-META/MMA-TBB resin was studied.Reduction of etching periods with 10-3 was not so effective as expected.The weakening of bond strength during immersion in water at 37℃ to the dentin pretreated for 1sec occurred faster than those for either 5sec or 10sec.The strength decreased from 12MPa at 1 day to 9MPa at 3 months, 3MPa at 6 months and finally 2MPa at 1 year in the case of 1sec pretreated dentin.On the other hand, the strength became half after the storage in water for 1 year in the cases of 5 and 10sec pretreated dentins.Combination of 10-3 pretreatment and subsequent glutaraldehyde treatment could stabilize the decrease but not completely.SEM and TEM examinations suggested that dentinal collagen exposed by the etching but not entangled and impregnated by poly(4-META-co-MMA)easily deteriorated by water during the longer immersion.Collagen modified with 10-3 and then with glutaraldehyde was also changed by the longer immersion.

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An excellent durability of adhesion was obtained in the adhesion of 2% 4-META/MMA-TBB resin to dentin pretreated with EDTA3-2(NH₄/Fe).Such high bond strength as 15MPa did not change for up to one year even when they were immersed in water at 37℃.The resin reinforced dentin, a hybrid, was identified between dentin and the cured resin by TEM.The collagen and hydroxyapatite were encapsulated with the copolymer and the crystals were not removed by the demineralization with either HCl or electronic staining.Tensile fracture between the hybrid and dentin like the adhered samples to 10-3 treated dentin did not occur and the cohesive failure in the resin was observed here after the storage in water for a year.EDTA3-2(NH₄/Fe)could not completely demineralize the hydroxyapatite especially at the deeper portion and the width of the demineralized dentin became thinner than 1μm.The encapsulated crystals with the resin could improve the resistance of collagen against deterioration in water and such good bonding durability could be obtained.

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To obtain inlay, crown and bridge types of titanium castings with sufficient size accuracy, zirconia investments with 10mol% calcia were studied for their setting expansion, thermal expansion, total expansion, casting shrinkage compensation deficiency on fabrication method, particle size of zirconia, calcia and mixing liquid.Addition of calcia caused the change from contraction to expansion in setting and the additional thermal expansion at 900〜1, 200℃.The choice of calcia and mixing liquid makes great influence on setting expansion, which is grouped into saturation type and delayed expansion type.By the use of the saturation type, total expansion could be controlled in the range of -2〜+3%.Titanium castings of inlay, crown, bridge types with the values -2〜+2% of casting shrinkage compensation deficiency could be successfully obtained.The casting shrinkage of titanium was estimated as 1.8〜2%.The castings have the surface with a metallic brilliance as cast.

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Adhesion between dentin and MMA resin was investigated using chemically activated initiator system consisting of 1, 3, 5-trimethyl-2-thiobarbituric acid, cupric salt, chloride ion, and tert.-butyl peroxymaleic acid(MA) with carboxyl group which usually has affinity to tooth.The adhesive strength of the MMA/PMMA resin to bovine dentin increased significantly to 8-10MPa by addition of MA, while the adhesive strength was 4MPa without MA.When the bonding broke at higher than 7MPa, the adhesive resin layer usually fractured cohesively and the interfacial fracture did not occur.The bond strength obtained in this experiment was comparable to that obtained with MMA resin using TBBO and ferric ion initiator system which is known as the best initiator system for dentin available.

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A new apatite-collagen complex was prepared in calcium β-glycerophosphate solutions at pH8.50.For this preparation, reconstituted type I collagen was cross-linked with phosvitin in the presence of alkaline phosphatase by use of a cross-linking agent of dimethyl suberimidate.After two weeks of immersion in daily-renewed solution of calcium β-glycerophosphate, the complex contained apatite approximately two times the modified collagen in weight.When viewed in a scanning electron microscope, needle-like crystals precipitated densely on the collagen fibrils.However, in some portion of the complex, dot-like precipitate was observed as well.X-ray diffraction and IR analyses of the complex suggested that the apatite precipitated on the collagen fibrils was very similar to bone mineral in two aspects, crystallinity and carbonate content.

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The fatigue characteristics of a zinc phosphate cement were examined.Using a split mould made of stainless steel, 12mm×φ6mm column shape specimens were prepared.Fatigue tests were done by loading partially repeated pulsating diametral tensile stress of 1〜20Hz, minimum stress was 0.2MPa(2.0kgf/cm²)and maximum stress was 3.5〜5.4MPa(36〜55kgf/cm²).During testing, the specimen was kept under distilled water.The existence of a fatigue was confirmed and there were marked signs of fatigue on the fracture surface.The relation between maximum stress and the number of cycles to fracture(S-N diagram) was obtained.Therefore the following equation and fatigue parameter(n) were deduced.logS+0.0775·logN=0.8931 n=12.9 The fatigue characteristics depended on the frequency, that is, a time to fracture was shorter at the loading frequency of 20Hz than that of 1Hz.

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The water sorption and desorption, and the diffusion coefficients of the water sorption and desorption were studied on the experimental composite resins with various filler contents in both chemically-cured and light-cured type.As the filler content increased, the rate of the water sorption and desorption on the composites decreased.And these properties associated with the prediction obtained from the law of mixture.The filler did not absorb water, so the effect of the filler content on the diffusion coefficients of the water sorption was to be associated with of the law of mixture.However, in the diffussion coefficients of the water desorption the effect of filler content could not be proved to be associated with the law of mixture.The diffussion coefficients of the water desorption were over 2 times larger than the those of the water sorption.

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As a model experiment to understand the mechanism of adhesion of the 4-META-MMA/TBBO resin to dentin, 4-META-MMA/TBBO was polymerized in the presence of decalcified dentin sheet treated with citric acid(CA) aqueous solution containing ferric chloride(FC).Curing time of MMA/TBBO resin was reduced by the addition of 4-META to MMA.Addition of 4-META increased molecular weight of PMMA.PMMA polymerized inside the decalcified dentin sheet was insoluble in acetone.PMMA obtained from the monomer liquid used in commercial Super-Bond C & B was all insoluble and no soluble fraction was obtained.These results suggested that 4-META accelerated polymerization of MMA-TBBO resin in the presence of ferric ion and was effective to enhance molecular weight of PMMA.These effects seemed to be related to high bond strength of Super-Bond with dentin.

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Effect of adhesion promoting monomers dissolved in photocurable bonding agents on adhesion to ground dentin was investigated.They were MDP, Phosmer-M and 4-MET.The effect of those monomers was compared with that of Phenyl-P.The bonding agents contained campherquinone(CQ) as a photosensitizer, N-phenylglycine(NPG) as a reducing agent and TEGDMA as a base monomer.Phenyl-P was the best adhesion promoting monomer among those studied monomers.MDP could not polymerize well enough to give good bond strength.Phosmer-M could permeate through the smeared layer but could not make a stable resin reinforced dentin.4-MET did not permeate through the smeared layer and did not adhere to ground dentin.

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