In previous studies, the present authors examined the discoloration of esthetic restorative materials, which might be mainly caused by the condition of the elements of the materials and the hydrogen sulfide gas. From the results of those studies, the causes of the discoloration were, supposedly, not only the combination of the elements and the hydrogen sulfide gas but also the physical aspects of the specimens: surface conditions, structures and properties. They measured the surface roughness of the specmiens to estabish the relationship between the color shift and the surface conditions. They further confirmed the existence of sulfur on the surface of the specimens, and examined the relationship among the discoloration, structures and properties of the specimens. The results were as follows: 1. The surface roughness of the specimens exposed to the hydrogen sulfide gas showed larger roughness than that of the specimens exposed to the air. 2. The two-dimensional analysis by an electron microprobe x-ray analyzer detected more sulfur in all of the specimens exposed to the hydrogen sulfide gas. Thus detected sulfur on the specimens exposed to hydrogen sulfide gas showed no significant difference in its concentration and distribution, that might clearly indicate that the hydrogen sulfide gas generated the sulfide on the surface of the specimens which had nothing to do with the color differences.

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The measuring conditions of amalgam dimensional change, specimen length, amount of alloy, measuring time and direction, were reconsidered by applying the “Double-cap” method to avoide the effect of the initial flow due to measuriing load. The dimensional changes of three alloys were measured by means of an electric micrometer. The effect of initial, medium and final flows was completely restricted by applying the “Double-cap”. The effect of the specimen length was insignificant by the “Double-cap” method, while a shorter specimen exhibited more shrinkage in measuring without the cap. The amount of alloy and the measuring time were significantly effective to certain alloy in measuring with the cap. The suitable testing conditions indicated are: 1) Apply the “Double-cap” 2) Prescribe the specimen length to 4mm 3) Start to measure immediately after condensation.

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For objective comparison of dentail reproduction of impressions, test blocks are required to prove that widths and angles of the carved lines are all in the defined range, and they should be available to researchers when necessary to get the same fine blocks. The authors, in the present studies, conducted to product test blocks satsifying these requirements. First of all, original pattern of the test block was prepared with lines carved in accrdance with ISO1563, and the accuracy in cross-sectional shapes of lines were confirmed by means of Surface Roughness Analying System^*. Next, ruled test blocks were duplicated by electroforming from original pattern, and their accuracy is also confirmed by the same method. As a result, it proves that all the duplicated lines are almost the same as the original pattern ones. Conseqently, it proves that by the present method, test blocks satisfying the above-mentioned requirements can be mass-produced, and another merit is that by using the present method, original pattern can scathelessly be reserved for future use. Again, it proves that the test block prepared by the present method show satisfying efficiency as those for specification test. (^*Surflyzer-Surfcom 703 B, Tokyo Seimitsu Co, Ltd., Tokyo)

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Corrosion and discolaration of Chromium-Nickel alloys were studied by placing the alloy specimens in 0.01N HCl, 0.05% HCl, 1% Lactic acid, Saline, humans saliva, 0.01% Na_2S and 0.1% Na_2S+1% Lactic acid mixture for 3-21 days, and then measured weight loss, concentration oa disolved metallic ion, spontaneous electric potential and color difference of the surface of chromium-nickel alloys bridge. The results indicated that the amounts of weight loss and metallic ion in 1% lactic acid or 0.01N HCl could be related to the chromium content of the alloys. When chromium content excess 12% very little corrosion and discoloration was observed.

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In order to measure the density of higher-melting dental metals in a wide temperature range from room temperature to about 1700℃, the previous apparatus based on the sessile drop method was advanced. By using a graphite heater, the furnace was able to meet the demand for measurements at high temperatures. By completing the optical system, the sharp shadow of the sample was taken on film even at high temperatures at which the sample radiates intensely. A texture analyzing system was composed by combining a projector through a digitizer to a microcomputer and errors caused by analyzing were discussed. The systematic error of the analyzing system was given less than 0.08%. The density of pure nickel was determined with the apparatus and the analyzing system, and the satisfactory results were obtained. Namely, the apparatus and the analyzing system were proved to be very useful to investigate the thermal shrinkage of higer-melting dental metals.

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Surface detail reproducibility of the indirect models made by the combination of various impression and cast materials was evaluated using both original models having the fine cut lines, and several knoop or micro-vickers indentations. The results obtained were as follows. 1. Modern elastmeric impressions were excellent in their reproducibility of both the fine line and the small indentations in the combination with any cast materials. However, a newly developed siliconised alginate and the conventional alginates were definitely inferior. Agar or agar-alginate combined impressions showed great difference in the ability to reproduce the fine surface details depending on the cast materials poured. 2. Crystal morphology such as the shape, particle size and void spaces among crystals, would greatly affect the surface characteristics of indirect models. 3. The indentation pattern reproduction test could more clearly demonstrate minute detail with SEM images than the fine line reproduction test.

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Recently the rare earth metal-cobalt magnets, namely Sm-Co, have been developed. The properties of this magnet are much better than that of the previous ones, such as alnico or ferrite magnet. By using the Sm-Co magnet, good results have been gained in the field of dental science, especially in the prosthetic dentistry. Lately Pd-Co-Ni casting alloys which have soft ferromagnetic properties have been developed. At present time, it has been understood by many clinicians that the alloy was very useful in the mouth to use the magnetic force of the Sm-Co magnet. I this paper, the new Au-Co-Ni casting alloys for dental magnetic appliance have been studied. Ranges of solidification temperature, mechanical properties, magnetic properties, microstructures and corrosion resistance have been examined. Results were as follows: 1) Au-Co-Ni alloys have satisfied soft ferromagnetic properties for dental use.Especially, increasing Co content, high magnetic saturation (10〜13kG) was gained. 2) Low melting temperature (1035〜1040℃) were obtained on the high karat compositions. On the other compositions, melting points were less than 1270℃. 3) Mechanical properties were enough for dental use. 4) Corrosion resistance of Au-Co-Ni alloys were not so good for a solution of 1%NaCl.

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We reported previously that adhesive bond strength to dentin decreased to 6 MPa on phosphoric acid etched dentin and adhesive failure at intertubular dentin and peritubular dentin were observed. Effect of glutaraldehyde pretreatment before the etching was studied and we found that the bond strength increased to 11 MPa. The improvement suggested that the collagen crosslinked with the aldehyde possessed stronger resistance against acid. The mixed failure modes were obsrved on fracture surface of the modified dentin after the tensile adhesive test. The resin reinforced dentin which was prepared by interpenetration of monomers into the dentin and the polymerization in situ was analyzed chemically and scanning electron microscopically.

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Carbon fiber cloths were used to reinforce polymetylmetacrylate resin for the palate of upper resin complete dentures. The cloths were incorporated being sandwiched with the resin. To increase affinity of the carbon fiber to the matrix resin, the cloths were treated chemically: 1) oxidation with chlorate solution, 2) introduction of carbon-carbon double bonds by esterification of the hydroxy groups produced on the surface wtih methacryloyl chloride and that of the carboxy groups produced with thionyl chloride or ethylene glycol followed by treatment of methacryloyl chloride, and 3) introduction of n-alkyl groups by esterification of the hydroxy groups with lauroyl chloride, and otherwise were covered by epoxy resin. The reinforced resins, especially in the case of the epoxy resins treatment, were improved in bending strength by twenty five percent and in tensile strength by fifty percent.

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Compositions of seven visible light-cured composite resins were examined, and amounts of monomer eluted from these cured resins were measured by means of high performance liquid chromatography. As base monomer of these materials, Tri-EDMA, Bis-GMA, Bis-MPEPP and/or UDMA were used as similar as the conventional chemically-cured composite resins. For one material, new monomer, Di(methacryloxymethylene)-tricyclo [5.2.1.0^{2, 6} decane was contained. Inorganic filler contents of these materials varied from brand to brand, and were in the range of 32 to 80wt%. Two kinds of these used the conventional large fillers, the size of which were in the range of about 0.2 to 20μm. Other five kinds used microfillers, and four kinds of these contained the organic composite fillers. The amounts of residual monomer eluted from these visible light-cured composite resins with one-month acetone extraction, were about 2 to 7 times that of the chemically-cured composite resin. In a comparison of amounts of monomer eluted from seven visible light-cured resins, that of two kinds which contained the conventional fillers in quantity were lower than that of the other five microfilled composites.

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The heterogeneities of polymerization of visible light-cured composite resins were investigated by measurments of Knoop hardness and residual monomer in these cured resins. In longitudinal section of specimen, conversion of resin was slightly lower immediately beneath the surface irradiated with light, and became maximum near 0.5mm beneath the surface, and then gradually decreased with depth. In horizontal section of specimen, conversion of resin was highest at center portion and gradually decreased toward cavity wall side. This heterogenities of polymerization were improved by increasing irradiation time and aproaching the light on the surface of material as near as possible. On the basis of hardness (conversion of resin) of chemically-cured composite resin, the clinically effective depth of cure of visible light-cured composite resin seemed to be in the range of 30 to 40% of the apparent depth of cure which generally called “depth of cure”. The visible light-cured resins had more residual monomer than the chemicallycured resin, and which was attributable to the heterogenities of polymerization of the visible light-cured resins. In visible light-cured resins, the material which contained more inorganic fillers with good light permeability, had less residual monomer than ones which contained less.

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The object of this report is to clear the effect of irradiation with ⁶⁰Coγ-ray and neutron beam on bovine mandible. Compressive strength of bovine mandible was temporarily greater at irradiation dose of 1×10⁵r with ⁶⁰Coγ-ray than that of unirradiated sample, and then the strength decreased with increasing irradiation dose. In contrast compressive strength of bovine mandible irradiated with neutron beam dereased rapidly with increasing irradiation dose. When bovine mandible was irradiated with ⁶⁰Coγ-ray or neuron beam, (002) peak of 2θ=25.8°appeared clearly in the X-ray diffraction patterns of the samples, and crystallinity of bovine mandible rose slightly. It was found from the X-ray diffraction patterns that bone apatite was more strongly affected than dentin apatite by irradiation with ⁶⁰Coγ-ray neutron beam. Weight loss (TG curve) of unirradiated bovine mandible was about 24% at 500℃, and was approximately equal to that of bovine mandible irradiated with ⁶⁰Coγ-ray. Howevere, weight loss of bovine mandible irradiated with neutron beam for 40 min. was about 15%.

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In addition to sufficient bond strength of the brackets to surface of the teeth, the removal of the brackets from the teeth after active treatment has been one of the requisites. Fluoride, as a inhibiting factor on adhesion, and on the otherhand, as a preventive factor against dental caries, was considered. The phosphate solutions containing fluorides of 0〜10% (w/v) (sodium fluoride, ammonium fluoride) were used as surface treatment agents before direct-bonding. Orthodontic metal brackets were directly bonded to extracted human teeth with three orthodontic adhesives. The tensile strength of Concise and System 1 falled by the addition of fluorides, but that of Super-Bond had not such a tendency. SEM analyses after treatment showed the changes of surface properties, for example, appearances of membranous deposits. X-ray diffraction and electron microprobe analyses suggested that calcium fluoride may be formed on the tooth surface.

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In order to obtain an accurate impression, it is important to determine the working and setting time of impression material. The determinations of the working and setting time, by assessing elastic recovery than any other properties of impression materials, are more realistic and critical. The authors introduced the pulsating rheometer as an instrument for measuring changes in elastic recovery during setting. The purpose of this investigation is to measure the amount of elastic recovery during setting and to determine the working and setting time of commercial alginate impression materials. Zelgan, Algifit new mix, Orthojel and Algipaste had short working time. These materials must be worked as quickly as possible after mixing. The setting times of alginate impression materials used in this investigation were shorter than those of elastomeric impression materials. The values of elastic recovery at the setting time of all materials tested, except Orthojel, were 95 to 98%, which were lower values compared with those of elastomeric impression materials. The elastic recovery of alginate impression materials deteriorated as the duration of strain increased.

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The five kinds of conditioners of dentin surface were prepared in order to improve the adhesive property of glass ionomer cement to the dentin. When 5% EDTA solution or 10% L-ascorbic acid solution was used as conditioner, observation with SEM showed that smear layer on the dentin surface was removed clearly but tubule apertures were not widened, and the adhesive property of the cement became higher. When the dentin was treated with 10% citric acid solution and then with 10% ferric chloride solution, the highest cement adhesive strength value, 63kg/cm² was obtained.

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Viscosity changes of dental zinc phosphate cements in early setting process by mechanical mixing mentioned in our recent paper were compared with those by hand mixing. Those were investigated using Viscometer VT24 which has a cone and plate system (HAAKE Inc.West Germany). About 0.04ml of cement mixture was required for this measurement. Cement mixture attained environmental temperature at the start of the measurement and maintained at the same temperature. The results obtained were as follows. (1) Viscosity Changes were affected by environmental temperature (23, 30 and 37℃). The higher environmental temperature was, the larger was the increasing rate of viscosity. (2) The increasing rate of viscosity measured at 37℃ of cement mixture by mechanical mixing was small at the beginning of the measurement. This stage became long as the ratio of powder to liquid became small. After 0.6〜1.25 min, the increasing rate became almost the same as that of cement mixture by hand mixing. (3) When cement mixture by mechanical mixing was stored on the glass slab at 23℃ for 1 min immediately after the mixing, the increasing rate of viscosity measured at 37℃ was almost the same as that of cement mixture immediately after hand mixing.

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