The dimethacrylates, EpDMA and BdDMA, which have a bisphenol type epoxy chain and butadiene chain in their main chains, respectively, were synthesized.The properties of the terpolymer composed of EpDMA, BdDMA and MMA monomers were examined.The monomer mixture of EpDMA, BdDMA and MMA was used as the liquid of denture base resin, and the properties of the cured resin were examined.
 The polymerization shrinkage of the terpolymer of EpDMA-BdDMA-MMA decreased with the increase in the EpDMA concentration in the cured resin, and the transverse strength and the elastic modulus were greatest at the BdDMA concentration of 0.3〜1 vol%.
 The denture base resin produced using a monomer mixture as the liquid, the transverse strength and the impact strength showed the highest values of about 110 MPa and 14KJ/m², respectively, at the liquid composition of 10 vol% EpDMA, 1 vol% BdDMA and 89 vol% MMA.

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 The effects of the shrinkage stress on the various cavity forms, were examined.The shrinkage stress was obtained from the displacement of the brass mold developed by polymerization of the composite resin.The shrinkage stress developed in the cavity wall, was analyzed by the finite element method, and the crack of the cylindrical silica tube filled with composite resin, was observed.
 The shrnkage striese 30 minutes after mixing the composite resin was reduced with the increase in the marginal angle as well as the diameter or the depth of cavity.Preparation of the bevel at the cavity margin reduced the shrinkage stress.In the case of reverse bevel, reduction of the stress was not observed within 24 hours, but in the other cases, the stress immediately decreased after hardening.The analysis by the finite element method reveoled the maximum stress at the margin, with less stress for the round, flat and reverse bevel in this order.
 For the observation of the cylindrical silica tube filled with composite resin, the crack was observed in the cylindrical silica tubes prepared round, flat or without bevel, it was not observed in the tube prepared reverse bevel that the crack was developed in this tube and composite resin was detached form this tube within 24 hours.

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 This study evaluated the cytotoxic effects of three common restorative materials on early passage cultured cells derived from human gingiva (HG cells) . Other early passage cultured cells derived from human dental pulp tissues (HP cells) and L cells established obtained from mouse subcutaneous tissues, were also examined.
 Cytotoxicity was assessed according to the uptake of neutral red and dye exclusion with nigrosin.The cytotoxicity was in the order of glass ionomer cement (highest) , light cured composite resin and dental amalgam. HG cells were the least sensitive to the materials tested.Both filtration of extracts and addition of serum into the extract affected the cytotoxicity. Glass ionomer cement increased the acidity of the extract, but the two other materials did not. Dissolution of metal ions, aluminium, tin, copper, mercury and zinc occurred from the materials. The extract of the composite resin had a different absorbance.
 This study disclosed differences in the cellular reaction to the restorative materials.Thus, utilization of early passage cultured cells is necessary for biological evaluation of the dental materials in vitro.

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 Ag - Cu binary alloys containing 5〜30% copper were subjected to dynamic extraction at 200 rpm and 37℃ to simulate the functional movement in the oral environment.Extraction was carried out in Eagle's minimum essential medium every two weeks for 18 weeks.The corrosion products were examined by the separation of extracts with a 0.22μm filter. Significant dissolution of copper occurred with increasing copper content, but the increase in silver dissolution was slight. The amount of copper in the filtrate was the same as that in the extract, but no silver was detected in the filtrate.Therefore, dynamic extraction accelerated the dissolution of copper from the Ag - Cu binary alloys and thus lowered the corrosion resistance.

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 The purpose of this study is to clarify a cause of disintegration for posterior composite resins by long-term immersion in distilled water during the 3 -year period.Three kinds of posterior composite resins [Bellfirm P (BP) , Clearfil Posterior (CP) and Micro Jar (MJ) ] and one conventional anterior composite resin [Clearfil F II (F II) ] were prepared as to specimens with 20mm diameter, and 1mm in thickness.These specimens were immersed in distilled water at 37±1℃ for 3 years.These specimens were observed by scanning electron microscope (SEM) .The residuces in distilled water were analyzed by X - ray microdiffractometry, infrared (IR) and nuclear magnetic resonance (NMR) spectrometers.
 One posterior composite resin (micropaticle filled resin) was eluted in water more than the other posterior and anterior composite resins with conventional fillers.
 In SEM observations, many air bubbles were found inside all sections of the four composite resins, because of all mixing type composite resins. The subsurface layer of all four composite resins showed signs of disintegration, but the center layer of the specimens was not disintegrated.
 Three cured composite resins except MJ had crystalline X - ray diffraction patterns before water immersion, but the cured MJ alone was amorphous. These peaks of crystals showed fillers of these composite resins respectively. X-ray diffraction patterns of the dissolved substances for three composite resins except BP were also crystalline, but the peaks of the crystals expcept CP were different from the peaks of the fillers respectively.
 In IR and ¹H-NMR spectra of dissolved substances, an unreacted monomer could be detected in one posterior composite resin (BP) , but not in the other composite resins.
 In ¹H-NMR spectra of dissolved substances, new signals not found originally were observed in all four composite resins.Therefor, the progress of disintegration was demonstrated clearly.
 The dissolved substances of all four composite resins were shown as the disintegrated substances between resin matrixes and silane coupling agents.
 It is suggested that the disintegration of these composite resins by long-term water immersion is derived from hydrolysis.

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 The adaptability of composite resin inlays was examined.CR Inlay and INLAY / ONLAY were used as materials.After the CR Inlay was polymerized in a U - form metal mold, the dimensional changes were measured before and after heating.Fhurthermore, the composite resin inlays made according to the manufacture's instructions were cemented in an MOD type cavity and the film thickness of the cement was measured.
 The polymerization shrinkage of CR Inlay was 0.63% in the inside of the inlay and after heating it increased to 0.71%.
 The film thickness of the cement in the case of CR Inlay was more than 250μm and that in the case of the INLAY / ONLAY was more than 750μm in the MOD type cavity.
 Dentacolor XS (a box type photo generator) was better than Wite Lite (a handy type photo generator) for the polymerization of CR Inlay.
 Because of the poor adaptation of the inlays and the difficulty in removing a inlay from a stone model for CR Inlay, perhaps polymerization shrinkage of the inlay should be compensated in some way.

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 Light - cured opaque resins with excellent physical properties were prepared using five types of monomer liquid and titanium dioxide as the powder.The five opaque resin monomer liquid had the following monomer compositions.Methyl methacrylate (MMA) / di (methacryloxyethyl) trimethylhexamethylene diurethane (UDMA) = 70 / 30 (M - U) , MMA / neopenthylglycol dimethacrylate (NPG) / UDMA = 45 / 45 / 10 ( M - N - U ) , UDMA / MMA = 70 / 30 ( U - M ) , 2 , 2 - bis (4 - methacryloxypolyethoxy phenyl) propane (2. 6E ) / 2, 2 - bis [4 - (3 - methacryloxy - 2 - hydroxy propoxy) phenyl] propane (Bis - GMA) / triethyleneglycol dimethacrylate (3G) = 60 / 35 / 5 (2. 6 - B - 3) and 3G / UDMA = 70 / 30 (3 - U) by weight.The bond strength, photo - curability and handling properties of the opaque resin were improved.
 Three MMA - based opaque resins showed nearly the same values in Knoop hardness number, diametral tensile strength and shear bond strength.The depth of cure increased with the decrease in MMA content of monomer composition, while the amount of residual monomer decreased.
 The 2. 6 - B - 3 opaque resin had nearly the same properties in depth of cure and Knoop hardness number as the 3 - U opaque resin.However, the 2. 6 - B - 3 and 3 - U opaque resins had a diametral tensile strength more than twice as high as that of the U - M opaque resin.The bond strength of three MMA - based opaque resins showed 0MPa after 5, 000 thermocycles, while the 2. 6 - B - 3 opaque resin, about 16MPa, and the 3 - U opaque resin, about 25MPa.
 Therefore, the bond strength of the opaque resin was influenced by monomer composition.3G - UDMA opaque resin showed excellent physical properties and may be clinically acceptable to bond fixed prosthodontic composite.

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The agar overlay method was modified and employed in this study to quantitatively evaluate the cytotoxicity of dental materials.The area of fibroblasts affected by the release of toxic substances from tested materials was determined with an image analysis system in order to compare the relative cytotoxicity of amalgams and composite resins.The cytotoxicity of amalgams decreased by 50% or more with aging time.Zinc appeared to be the major contributor to the cytotoxicity of amalgams.The cytotoxicity of chemically cured composite resins was also reduced with hardening time.However, even after 24 hours, the cytotoxicity of all chemically cured composite resins was still apparent.The cytotoxicity of light cured composite resins was dramatically reduced after illumination with the light source.The cytotoxicity of both amalgams and composite resins was strongly dependent upon their hardening process, since aging and curing produced a more stable material which was less likely to release toxic substances into the culture medium.The technique developed in the present study for measuring the area of affected cells to quantitatively evaluate the cytotoxicity of dental materials is simple and reproducible.

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A translucent aluminous porcelain was developed for dentistry.The effects of refractive indexes and sintering behaviors on transparency and strength of the aluminous porcelains consisting of high refractive germanate-glass(Na₂O-TiO₂-GeO₂)and alumina crystal powders were examined.The various germanate-glass specimens with a high refractive index were made by fusion at about 1, 300℃.The refractive indexes of fused Na₂O-TiO₂-GeO₂ glass specimens were 1.64〜1.76, heightened with an increasing TiO₂ content.The sintered aluminous porcelains were made from the mixed compacts consisting of 80wt% germanate-glass and 20wt% alumina at the densification temperature of 580〜820℃.Sintered aluminous porcelains prepared with high refractive germanate-glass had a high transparency compared with the other aluminous porcelains, with almost the same transparency as a commercial feldspathic porcelain(body).Aluminous porcelains had lower transparency with different refractive index due to generation of crystals following the crystallization of glass matrix than that without crystallizing property.Bending strength value was 120MPa, which is similar to that for the glass-alumina ceramics with the same content of alumina volume as germanate-glass aluminous porcelains.Non-crystallized aluminous porcelain had a higher strength compared with the crystallized one.

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Chitosan, a naturally occurring high molecule or weight polymer which is stable in vivo like collagen, has proved a useful biomaterial in applications such as suture thread and artificial skin.A hydroxyapatite bone-filling material was developed with chitosan sol as a binder.Measurements were made of the solubility of chitosan, and of the setting time, compressive strength, and pH value of the material.X-ray microanalysis and diffraction analysis of the material were also conducted.Chitosan is freely soluble in malic acid and succinic acid, but insoluble in citric acid and oxalic acid.The setting time of the bone-filling material tended to decrease with increase in the amounts of its CaO and ZnO components.The setting time increased with increasing ratio of sol to other(powdered)ingredients.The pH value decreased with increasing ratios of chitosan sol to the powdered ingredients.High pH values resulted from increases in both CaO and ZnO.The time between the preparation of the chitosan sol and the onset of kneading significantly affected the compressive strength of the material when set.The strength measured roughly 50% more for times between 90 and 150 minutes than for times shorter or longer than that range.Greater compressive strength was generally observed for increases in both CaO and ZnO.The results of the X-ray microanalysis of the hardened paste showed calcium crystals other than hydroxyapatite.

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Experimental gypsum-bonded investments containing 0.5〜5.0wt% NbC were prepared by mechanical mixing of each powder.Setting and thermal expansion measurement, compressive strength and casting accuracy for Ni-Cr alloy for metal-ceramic restoration were investigated.Analysis of NbC during heating was carried out by X-ray diffraction, TG-DTA and SEM.NbC was oxidized to Nb₂O₅ with a volume change between 300〜600℃, as in the following equation:
2NbC+4 1/2O₂→Nb₂O₅+2CO₂
The theoretical volume of 1/2Nb₂O₅ calculated from the lattice constants according to JCPDS file was approximately 4 times larger than that of NbC.The experimental investments of 70wt% cristobalite and 30wt% gypsum containing 2.0, 3.0 and 5.0wt% NbC showed large thermal expansion of 7.0, 10.0 and 13.0% respectively.The investment containing 2.0wt% NbC showed nearly the same casting accuracy for Ni-Cr alloys for metal-ceramic restoration as the commercial phosphate-bonded investment.

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The tracer element molten(TEM)method has been developed for flow visualization of molten Titanium in dental precision casting.The principle of this technique is as follows.When Titanium is cast, the tracer element wire inserted previously into the selective point of the sprue is molten little by little and distributed according to the molten Titanium flow in the mold cavity.After solidification, to observe the flow pattern, the tracer element needs to be analyzed on a section of the casting by EPMA equipped with the stage scan mapping system.This technique using Ag, Au, Pd or Pt as a tracer has been applied to some simple castings in shape and has been confirmed to be a very powerful technique for Titanium flow visualization in dental castings.

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The thermal properties(thermal diffusivity and thermal conductivity)of human teeth and some dental cements were measured.The temperature change at the pulp cavity was also measured before and after the restoration with the full metal crown.The thermal insulating efficiency of dental cement was discussed.The thermal diffusivity of human dentin, enamel and dental cements was 2.04×10^-3, 3.22×10^-3, and 0.99〜1.87×10^-3cm²/sec, respectively.The thermal conductivity was 1.36×10^-3, 1.84×10^-3, and 0.50〜×1.51×10^-3cal/cm・sec・℃, respectively.The dental cement beneath the crown insulated the thermal shock to dental pulp and the thermal insulating efficiency was increased with the decrease in the thermal diffusivity and thermal conductivity of dental cement.

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New experimental visible-light cured soft resins were prepared by combining a vinylidene fluoride/hexafluoropropylene copolymer(2-6F), or a vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene copolymer(2-4-6F)with 2, 2, 3, 3-tetrafluoropropyl α-fluoroacrylate(4FFA), 2, 2, 3, 3, 3-pentafluoropropyl α-fluoroacrylate(5FFA), 2, 2, 3, 3, 4, 4, 5, 5-octafluoropentyl α-fluoroacrylate(8FFA), or 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7-dodecafluoroheptyl α-fluoroacrylate(12FFA).Some properties of the resins prepared were measured to determine whether they would be candidate materials for the soft denture liner.Water contact angles increased with the increase in the number of fluorine atoms contained in the monomers:85〜90° in 4FFA, 90〜93° in 8FFA, and 92〜93° in 12FFA.Softer resins were obtained with 2-4-6F, especially by the combination with 8FFA giving the softest resin with a hardness of 43〜46(JIS A).Water sorption after 10 weeks was considerably low:0.4〜2%:0.4〜0.9% in 4FFA/2-6F and about 2% in 8FFA/2-4-6F.Solubility was 0.2〜0.4% in the resins with 4FFA and 1.0〜1.4% with 8FFA or 12FFA.Amount of residual monomer was low, and the maximum was 0.4% in the resin with 12FFA.Thus hardness and water sorption of the resins prepared were superior to those of the commercial soft materials.

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New experimental visible-light cured soft resins were prepared by combining a low molecular weight vinylidene fluoride/hexafluoropropylene copolymer(2-6FL), or vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene copolymer(2-4-6FL)with 2, 2, 3, 3-tetrafluoropropyl α-fluoroacrylate(4FFA), or 2, 2, 3, 3, 4, 4, 5, 5-octafluoropentyl α-fluoroacrylate(8FFA).Some properties of the resins prepared were measured to determine whether they would be candidate material for soft denture liner.Water contact angle was 90〜92° with 4FFA, and 90〜94° with 8FFA.The resins combined with 2-4-6FL were sufficiently soft:42〜46(JIS A hardness)in 4FFA, and 33〜39 in 8FFA.Generally the hardness decreased by 5〜10 with the use of a low molecular weight of fluoropolymer.Water sorption after 10 weeks was 0.8〜1.2% in 2-6FL/4FFA, 1.3〜1.7% in 2-6FL/8FFA, about 1% in 2-4-6FL/4FFA, and about 2% in 2-4-6FL and 8FFA.Solubility was 0.4〜0.5% in 2-6FL/4FFA, 0.3〜0.4% in 2-4-6FL/4FFA, 1.5〜1.9% in 2-6FL/8FFA, and 1.1〜1.5% in 2-4-6FL/8FFA.Amount of residual monomer was very low, and the maximum was 0.1%.Tensile strength of the resins was reduced to 40〜70% of that of the similar resins obtained in the previous study.Thus softer resins could be prepared by using lower molecular weight fluoropolymers.

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The influences of the composition on abrasion resistance of composite resins were examined using various experimental composite resins which had various matrix resin, filler size and content.The abrasion test was conducted by the experimental toothbrush abrasion testing machine developed in our laboratory.Three series of heat-curing composite resins were tested.One series was made from a Bis-MPEPP or UDMA monomer, and a silica filler with an average particle size of 0.04, 1.9, 3.8, 4.3, 7.5, 13.8 and 14.1μm.The filler content of this series was constant at 45wt%.The second series contained a silica filler of 4.3μm in a content ranging from 35 to 75wt%.The third series contained a microfiller(0.04μm)and macrofiller(4.3μm)in total content of 45wt%.In this series, the microfiller was gradually replaced by 5, 15, 25 and 45wt% of the macrofiller.The results obtained for these three series indicated that the abrasion resistance of composite resins was controlled by the incrganic filler, mainly filler size and content.The abrasion loss did not vary with the difference of matrix resin.When the particle size of the filler was below about 5μm, the abrasion resistance decreased markedly with the decrease in filler size.The composite resin which contained a 0.04 or 1.9μm filler was less resistant to toothbrush wear than the unfilled matrix resin.However, the microfiller also contributed to abrasion resistance when used in combination with the macrofiller, although abrasion resistance decreased with the increase in the microfiller concentration.The increase of filler content clearly improved the abrasion resistance when used the macrofiller.The analysis of these results and SEM observations of the brushed surfaces of samples suggested that the toothbrush abrasion was three-body abrasion caused by the abrasive in the toothpaste, and affected by the difference in the particle size between abrasive and filler, and between the abrasive size and the interparticle distance of the filler.

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To measure the three-dimensional shape of the undercut portion of a molar model tooth, the tilting method was used.The measuring system was composed of a laser displacement meter with double sensor and a computer controlled tooth model scanning machine(CAMM-3).A model tooth was tilted on the gonio stage with±20° and measured divisionally, and a couple of data were connected by the TILCOMPO program.The undercut portions from the survey line to the tooth neck were measured and drawn by CG.By this tilting method, the whole shape of tooth including the undercut portion could be measured, and these data will be available for the production of the data base for CAD of prosthesis.The marginal line on the crown abutment measured previously was searched.Initially, the difference in the inclination dz/dx between the data before and behind was calculated, and the gingival line was extracted by limiting its value.Then, also by limiting the difference value, the margin located above the gingival line was determined.Thus the marginal line in contact with the inner and outer crown and a significantly important point for the production of crown by the CAD/CAM technique could be determined around the crown abutment.Another elementary attempt to simulate the occlusion by using the data of teech models measured on the articulator was carried out.The maxillary and mandibular teeth were set on the articulator and the maxillary teeth turned over.The shapes of the 5〜7 upper and lower molar were measured.The two data were connected and occluded by the"OCCLUS"program.By turning the maxillary teeth reversely, the small amount of occlusal contact appeared and by further increase in the reversing angle, the growth of degree and area of occlusal contact could be simulated.Thus, the assumptive state of occlusion could be simulated by this method and the occlusal adjustment by computer will be possible.

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A new database system of literatures on dental materials and devices was developed by the Committee for the Database, the Japanese Society for Dental Materials and Devices, with the cooperation of the members.The procedure for the informaton retrieval using on-line system(N1 network system)was shown with examples.

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