The visible light-cured composite resins cure only up to a certain depth beneath the surface irradiated with light, in different from the chemically-cured composite resins. This depth is called “the depth of cure”, and vary with some factors. In this study, factors affecting the depth of cure were examined. For the same brand, the depth of cure varied with the differences of shades of resins. Hence, the irradiation time should be selected with the shade of resin. The depth of cure increased as the irradiation time was extended, and decreased as the irradiation distance was extended. This depth also varied with setting positions of irradiation rod of activator lights. This depth was influenced with cavity materials, the depth of cure in ivory cavity with light permeability was about 1.2times that in steel cavity without light permeability.

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It is thought that the depth of cure of visible light-cured composite resin is dependent on intensity of activator light. In this study, depths of cure of all combinations of seven visible light-cured composite resins and seven actvator lights were measured and compared, in addition, the spectrum of the radiation emitted from each activator light unit was measured. From these results, the relation between the depth of cure and intensity of light was discussed. For the same material, the depth of cure varied with activator light used for polymerization. However, all of them, except on light, showed the almost similar depth of cure for almost materials, and it seemed that almost material could be polymerized with any activator light except one unit. The spectrum of each activator light showed the different pattern, respectively. It should seem that the depth of cure of material was related to the intensity of light determined from these spectra in 410 to 500nm region, where the photosensitizer (comphoroquinone) absorbed. When the same activator light was used, the depth of cure of material varied from brand to brand and with the shade of resin.

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The experimental adhesive resins consisted of MMA, 4-META, PMMA, TBB-O (: same as Superbond C&B), and their tensile adhesive strengths to ceramics were investigated with and without silane coupling agents in comparison with Panavia-EX. As adherend, porcelain for metal-ceramics VITA VMK68 dentin, opaque and one of dental implants BIOCERAM (; single crystal of alumina, Kyocera Corp.) were used. Experimental resin and Panavia-EX adhered a little to those adherend. And expermental resin with 1% silane coupling agent showed higher adhesive strength to ceramics than the experimental resin without silane. But any adhesives was not considered to have enough stability for longterm Clinical application, because of the lack of endurance of tensile adhesive strength after long period water immersion. The experimental resin with 1% of silane coupling agent revealed the excellent adhesion to BIOCERAM (its adhesive strength was nearly 200kgf/cm² after 1 month water immersion period). On the other hand, the tendency to failure of porcelains, whcih were adherend, was examined. Panavia-EX was apt to cause adherend-failure. But in the experimental resins such a phenomenon was not observed.

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In order to accumulate the fundamental data on discussing the flow characteristics of Bis-GMA composite resins, Bis-GMA + TEDMA monomer mixtures at each of the following rates were measured by coneplate type rheometer: 10 : 0, 8 : 2, 7 : 3, 6 : 4, 4 : 6, 2 : 8, 0 : 10. Each mixture was added an inorganic filler and they were also measured by that rheometer. The viscosity vs time curve and the flow curve were studied at four temperatures in the range of 20℃ to 37℃. The composites were studied at five percentages in the range of 60wt% to 75wt% filler mixed with Bis-GMA 70wt% + TEDMA 30wt% monomer mixture. The results were summarized as follows. Bis-GAM, TEDMA and Bis-GMA + TEDMA monomer mixtures were Newtonian. As the amount of TEDMA increased, the viscosity of Bis-GMA + TEDMA monomer mixtures decreased. Bis-GMA + TEDMA monome mixtures showed the Andrade type viscosity change in the rnge of 20℃ to 37℃ and the relationship between the logarithm of apparent activation energy and mol ratio of Bis-GMA + TEDMA monomrer mixtures was linear. The composite of monomer and filler showed thixotropy which was increased by the amount of filler. Thixotropy was decreased by the rise of temperature from 20℃ to 37℃. It showed the Andrade type thixotropy change.

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The correlation between permebility and castability was investigated using four dental casting techniques (centrifugal, normal air pressure, peripheral air pressure and vaccum casting). Four dental investments, which had different permeability coefficients, were utilized for this study. Coil type wax patterns were used for measuring the castability (Fig.1). Shell type investment samples for measuring the permeability were shaped by silicone rubber cut mold. Castability was indicated by casting ratio which is the value of cast length divided by the whole length of coil pattern. Permeability of investment sample was measured at casting temperature by the method described in the second report. The effect of permeability on castability was changed due to casting methods. 1. In centrifugal and normal air pressure castings, higher permeability gave higher casting ratio. 2. In peripheral air pressure casting, higher permeability decreased casting ratio. 3. In vaccum casting, higher permeability increased casting ratio.

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It was reported in the previous part that the expansion, especially the setting expansion of the phosphate-bonded investment was significantly changed by some alterations of the mixing condition. The expansion was also markebly different among the different lots of each commercial product. In the present study, it was examined how these variations of the expansion might affect the dimensional accuracy and fit of the Ni-Cr alloy castings. The casting ring was lined with a sheet of ceramic liner. The hexagonal rod castings became larger than their original wax patterns except for one investment wihch is adjusted by the manufacturer to bring lower setting expansion and higher thermal expansion. Although the casting shrinkage of Ni-Cr alloy could thus be compenstated, the cast crown showed discrepancy between its margin and the abutment die in most cases. As the setting expansion increased, the dimension of the rod casting increased and the discrepancy of the crown decreased. No discrepancies could be found when a lower L/P ratio of the investment was selected and the setting expansion became maximum. The marked variations of the setting expansion among the different lots of the investment was also reflected on the significant differences in the fit of the crown.

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The purpose of this paper is to clarify the softening temperature of porcelain for metal-ceramics. Thermal expansion curves were investigated and softening temperature under load and flow rate were measured. Following results were obtained. 1. The temperature in which the thermal expansion coefficient decreased or shrinkage initiated on the thermal expansion curve was not softening temperature of porcelain. It seemed to be firing shrinkage. 2. Softening temperature under load from 1, 000kgf/cm² to 20kgf/cm² was above 600℃ and stress relaxation due to flow of porcelain was not produced below 600℃. 3. The viscosities of opaque porcelains were calculated from flow rate as a function of temperature. Softening temperature and strain temperature were determined comparing with the viscosity of typical glass. Softening temperatures of opaque porcelains were about 861℃ in Jelenko, about 900℃ in Ceramco, and about 846℃ in Vita. Strain temperatures of opaque porcelain were about 527℃ in Jelenko, about 497℃ in Ceramco, and about 526℃ in Vita.

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In the previous paper, the new Au-Co-Ni casting alloys for dental magnetic appliance was studied. And the magnetic properties, melting temperature, mechanical properties and corrosion resistance of the alloys were reported. As a result, it was found that some Au-Co-Ni alloys had satisfied properties as dental casting ferromagnetc alloys, except to the corrosion resistance and fluidity. To improve those probrems, Pd, Cr and Si were added to selected compositions of the Au-Co-Ni alloys. The effect of such alloying elements on the Au-Co-Ni alloys was studied in this paper. Magnetic properties, range of solidification, crrosion resistance, mechanical properties, microstructures and magnetic attraction to Sm-Co magnet were examined. Results were as follows: 1. Crrosion resistance was improved by adding 15%Pd or 2%Cr and more. 2. The fluidities of Au-Co-Ni ternery alloys could be improved by adding 0.2%Si. 3. 34.8Au-15Pd-30Co-20Ni-0.2Si, 47.8Au-2Cr-30Co-20Ni-0.2Si, 66.8Au-10Pd-14Co-9Ni-0.2Si and 74.8Au-2Cr-14Co-9Ni-0.2Si were excellent as dental casting ferromagnetic alloys.

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A hydroxyapatite-polyacrylic acid composite cement (hydroxyapatite-glassionomer cement) was prepared. The compressive strength of the cement increased as the heating temperature of hydroxyapatite. The highest strength of the cement was about 1, 300kg/cm². In this cement, hydroxyapatite heated at 1, 400℃ was used. The compressive strength of the cement depended on the P/W and on the quantity of tricalcium phosphate in hydroxyapatite. The setting reaction between hydroxyapatite and polyacrylic acid was mainly due to the formation of the COO-Ca bonding. This composite cement was investigated histopathologically by using 10 young human teeth. The pulpal reaction was remarkably lower. It caused no unpleasant feeling to patient and no pulp death during the period of 1 month after operation.

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In the investigations of reinforcement of denture base polymethylmetacrylate resins with carbon fiber cloths, effects of thickness and number of the cloths on bending, tensile and impact strength, and safe limit evaluated from transverse-deflection value according to the American Dental Association (ADA) specification of the composite were studied. The composite specimens were fabricated with; 1) single sheets: 0.1, 0.2, and 0.4mm thick cloths pretreated by the epoxy resin (ECF) and by the lauroyl chloride (LOCF), 2) pile sheets: two and four sheets of 0.1mm thick ECF. In cases of ECF cloths, the physical properties of the composite resins increase with thickness and number of the CF pile sheets, while in cases of LOCF cloth these were unchanged. Based on the transverse-deflection values according to the ADA specification, it was recognized that the upper limit of thickness was 0.2mm ECF in cases of the single sheets, and that of number of the CF pile sheets was two in cases of the ECF sheet of 0.1mm thick.

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Seven commercial nickel-chromium casting alloys for crowns and bridges were studied with respect to the effects of microstructure, investigated by X-ray microanalysis, on electrochemical corrosion behavior: rest potential and anodic polarization curve in Ringer's solution at 37℃. The results are summarized as follows. 1. Nickel-chromium alloys containing a high amount of many additional elements showed a complex microstructure, consisting of segregation of elemental components, eutectic structure or preciptation of carbide or boride etc. 2. Rest potential value (vs.SCE) of nickel-chromium alloys containing molybdenum or copper shifts toward more noble potential than that of the alloys without them. 3. Nickel-chromium alloys containing tungsten, carbon or boron showed a microstructure consisting of the precipitation of various crystal phases and their rest potential value was more base potential than that of the alloys having homogeneous structure because of local cells between various phases. 4. Molybdenum has the same effect as chromium for increasing the resistance to pitting corrosion of nickel-chromium alloys in Ringer's solution. 5. Nickel-chromium alloys having the microstructure consisting of the segregation of elemental components or various crystal phases are susceptible to pitting corrosion because of local attack to the poor chromium region.

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Methacryloyloxyethyl hydrogen phthalate, methacryloyloxyethyl hydrogen isophthalate and methacryloyloxyethyl hydrogen terephthalate were synthesized and MMA-TBBO type adhesives containing these monomers were prepared. Adhesive strength of these Adhesives to the felt polished 14 kinds of elemental metals and 6 kinds of dental alloys was estimated by means of 2, 000 times thermal cycle test. Adhesive with methacryloyloxyethyl hydrogen terephthalate (MEtPh) showed highest adhesive strength of these three kinds of adhesives in spite of its low monomer concentration (below 0.5mole%). A little better adhesion was obtained in the case of adhesives with methacryloyloxyethyl hydrogen isophthalate (MEiPh) or methacryloyloxyethyl hydrogen phthalate (MEPh) in comparison with non-additive type. Adhesive strength of the latter two types of adhesives, however, decreased considerably after thermal cycle test. Of all the metals and alloys used in this study, zinc, aluminum and tin were observed to be excellent adherends for adhesives examined here.

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Biocompatibility of Fe〜30at%Pd alloys with shape memory effect was studied by anodic polarlization behavior in 1% NaCl solution and biological reaction of alloy implanted in the leg bone of hen. Natural potential of Fe-Pd in 1% NaCl solution was about -80mV (referred by SCE) and nobler than Ni-Ti with -240mV. However, by the result of anodic polarization, the passive breakdown potential of Fe-Pd was bout 450mV, and considerably lower than Ni-Ti with 1, 200mV. According to the results of animal experiments, 3 months after implantation, paticular swelling of bone by tumor which was observed in the case of Ni implantation was not observed. But at the boundary of bone and alloy, connective tissue was partly formed and significant dissolution of Fe was observed, and another contacting position of bone with alloy, partly dissolution of Fe was also observed.

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In order ot investigate the casting shrinkage of the dental alloys, the density of five gold alloys and Au-Pd-Ag alloy were measured at temperatures ranging from room temperature to about 1, 400℃ by using an apparatus which was based on the Sessile drop method and of which the reliability has been confirmed in previous work. The thermal and solidifying shrinkage were discussed on the densisties at room temperature, solidifying point and melting point which were determined from the curves showing the variation of density with temperature. The voluminal shrinkage during solidification of multi-component alloys was smaller than that of small-component alloys and the surface of the former having large dendrites was more smooth than the later having many shrinkage folds was. The growth of the dendritic structure during solidification causes many vacancies in the cast and results the small solidifying shrinkage.

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