The influence of initiator systems of visible-light curing resin on the polymerization behavior was investigated using DSC kept at 37℃.The experimental visible-light curing resin used here consisted of triethylene glycol dimethacrylate(3G)monomer, a photosensitizer and a reducing agent.The photosensitizers were dl-camphorquinone(CQ), 9-fluorenone(FL)and benzil(BZ), and the reducing agents examined were N, N-dimethylaminoethyl methacrylate(DAEMA), thiophenol(TP), 4-mercaptophenylmethacrylamide(MPMA), thiosalicylic acid(TSA), 3-mercaptopropionic acid(MPA), and 2-mercaptoethanol(ME).The most effective photosensitizer was CQ, and the CQ-DAEMA system gave the values of T(time at maximum exothermic peak)=0.6〜0.7 min, and R(maximum exothermic rate)=16〜18mcal/sec under the conditions employed.The addition of reducing agents containing SH group to 3G and CQ visible-light curing resins also resulted in the promotion of polymerization by visible-light irradiation.The tendency was more significant in the case of thiophenol derivatives, when compared with thioalcohol derivatives.Especially, TP exhibited an excellent acceleration effect in polymerization of 3G and the effect was comparable to that of DAEMA.

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The effects of five repeated casting cycles in six kinds of commercial non-precious alloys, their mechanical properties and components were studied.Nickel-chromium system alloys and cobalt-chromium system alloys were analyzed for molybdenum, tungusten and titanium as well as for the above expected alloys.Nickel-chromium system alloys were also examined for silicon, copper and molybdenum/non-molybdenum.Properties and components of alloys containing tungsten were not affected by repeated casting.Repeated casting of titanium containing alloys caused a decrease in titanium content and a marked reduction of tensile strength.Hardness and elongation of silicon containing nickel-chromium system alloys were affected due a decrease in silicon content.The addition of the same amount of new ingot to the recasting button did not alter the mechanical properties and components of the alloys.

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The flow of plaster from the beginning of mixing to setting and its properties under the forced vibration were analyzed in representative sample and those with final passing time.The flow of plaster mix increased with the vibration applied, but the flow did not exceed as the setting time.The flow of plaster mix was maximum 5 seconds after the beginning of vibration, and it decreased as the vibration time is prolonged.The flow tended to increase 5 seconds after the beginning of vibration when the amount of plaster mix was large, and this tendency increased as the vibration time was prolonged.The flow gradually decreased with the delay of vibration beginning time, but it decreased abruptly at the flow change time.The flow disappearing time, flow change time and final passing time of plaster mix were almost constant for a particular plaster mix regardless of the amount.Flow change time of plaster mix almost coincided with 5cm final passing time.Plaster mix showing the same consistency under static conditions exhibited quite different flow under dynamic conditions.

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Cylindrical specimens(4mm in diameter×4mm in height)of visible light cured composite resins were cured in white teflon mold by illuminating from the top for 10, 20, 40 and 60 sec and from the top and bottom for 60 sec each.Specimens were then stored in air at 23℃ for 30 minutes, in water at 37℃ for 24 hours, or in water at 37℃ for 7 days before testing.Compressive test was performed and compressive yield strength were calculated.Specimens stored for 30 minutes did not have sufficient strength, and the compressive yield strength could not be calculated for some specimens.Prolonged exposure times up to 40 sec increased the strength of the specimens but a 60 sec exposure had no clear effect.

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This study was undertaken to compare the marginal accuracy of ceramic core coping and metal coping in the porcelain-fused-to-metal system, and to investigate the shrink-free quality of ceramic core material.In anterior teeth(1), the mean mrginal discrepancy for ceramic core coping was 24μm, and for metal coping 71μm, whereas in posterior teeth(6), the values were 16μm and 63μm respectively.The margins in the ceramic core coping appeared more closely adapted than the metal coping.Scanning electron microscopic observation of the ceramic core materials disclosed a porous microstructure even at a firing temperature of 1315℃.Al, Si, Mg, Ca, Ba, Cr were detected by electron prove X-ray microanalysis.By X-ray diffraction analysis, the Al₂O₃, SiO₂, and MgO peaks were observed at firing temperatures of 4℃, 500℃ and 1200℃.And the spinel(MgAl₂O₄)peaks was observed when a firing temperature of approximately 1315℃ was reached.The results indicate that the aluminum oxide spinel occupies a greater volume than does the combination alminum and magnesium oxides reacting to from the spinel.Thus, there is a resultant volume increase sufficient to compensate for firing shrinkage.

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The purpose of this investigation was to develop a new method for measuring expansion during setting of dental investments and to discuss the results obtained by this method.A modified casting flask lined with kaowool or asbestos and gypsum-bonded investments was used.In the measurements are made through a glass plate put on the flask, the obtained values of expansion during setting show wide variation.Furthermore, the values were also markedly affected by the exudation of excess water from the investment.Therefore, we used a modified metal cover instead of the upper glass plate and sealed the flask to a bottom glass plate using vaseline.These modifications markedly decreased the variation of experimental results.We also found that the variation was greatly influenced by the interval between mixing and pouring into flask.

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We examined the synthesis of new dental resin monomers to clarify the conditions of synthesis and the properties of the monomers and bulk polymers.Octachlorocyclotetraphosphazene(4PNC)and 2-Hydroxyethylmethacrylate(HEMA)were reacted at 50℃ for 4〜100 hours, and synthesized(PNC-EMA).Of the 8Cl atoms of 4PNC, 7.72 were replaced by EMA(methacryloxyethoxy group)in 100 hours(PNC-EMA 4006).IR and XMA, revealed approximately linear relationships exist between the number of replaced EMA and the specific gravity and also the refractive index of synthesized monomers.With the increase in the number of replaced EMA, the compressive strength and the hardness(H_K, H_RS)of bulk polymers increased, but the transverse strength was minimum at 6.In the case of less than 6 in number of replaced EMA, the surface of bulk polymer were cracked after immersion in water at 37℃.The bulk polymer of PNC-EMA 4006, showed considerable chemical stability in water and satisfactory physical properties, with polymerization shrinkage of 9.36%, compressive and transverse strength of 4574 and 542kg/cm² respectively, H_K40.5, H_RS97.2 and coefficient of thermal expansion of 66.9×10⁻⁶/℃.After immersion in water at 37℃ for 1 week, the bulk polymer of PNC-EMA 4006, the compressive and transverse strength were 3200 and 380kg/cm² respectively, hardness was H_K20.0 and H_RS97.0.

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Sixteen Ni-base alloys composed of 10〜25wt%, Cr, 0〜15wt% Mo with Cr and Mo varying at increments of 5wt%, and Ni(60〜90wt%)were prepared by melting under a high-purity argon atmosphere and subsequent centrifugal casting.Tensile strength, elongation, Vickers hardness and resistance to tarnishing were measured.Orthogonal analysis of variance was made on the amounts of Cr and Mo, and an orthogonal polynomial function was determined to estimate the optimum composition of crown and bridge casting alloys.The tensile strength of the castings increased with Mo content, but decreased at 15wt% Mo and 25wt% Cr.Alloys with a tensile strength of 65kgf/mm² or more were in the range of 15 to 22wt% Cr and 12 to 15wt% Mo.The elongation of the castings showed a maximum value of about 27% with alloys of 17wt% Cr and 11wt% Mo.Vickers herdness increased with Cr and Mo content, reaching 218 at 25wt% Cr and 15wt% Mo.The brightness L* after 3 days of immersion in a 1% lactic acid0.1% sodium sulfide mixed solution at 37℃ increased with Cr and Mo content when Cr content of an alloy 15wt% or more, and an improvement in resistance to tarnishing was noted.The alloy containing 69wt% Ni-18wt% Cr-13wt% Mo appeared to have a maximum tensile strength, allowances being ±2 and ±1wt% for Cr and Mo, respectively.Tensile strength, elongation, Vickers hardness and brightness L* of this alloy were 67±4kgf/mm², 25±5%, 188±4 and 71±1, respectively.

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Mechanical properties of light and heat cured resins were compared to understand their characteristics using the same formulation except the catalyst.Their surface hardness and an amount of water sorption were only slightly affected by the curing process.However, the compressive strength and abrasion resistance of the heat cured resins were greater than those of the light cured resins.Scanning electron and light microscopic observations indicated that abrasion loss occurred over the entire area in the light cured resins, compared to regional change in the heat cured resins.Thus, light cured resin matrix appears to be weaker than that of the heat cured.

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Light-activated composite resins were experimentally prepared from a silica filler and several kinds of dimethacrylates as base resins to study the relationship between their refractive indices and the depth and degree of cure of the resin.The monomer that had a similar refractive index to that of silica transmitted light effectively and was well cured by visible light and ultraviolet ray.Since the refractive index of the base resin became larger with polymerization, the transmittance of the cured resin containing a filler decreased markedly.All the resin monomer/silica filler pastes and those cured products transmitted more visible light than ultraviolet ray.The degree of cure was tentatively evaluated by the rate of the decrease of Knoop hardness inward from the surface irradiated with light, and was related to both the refractive indices of monomers and those of polymers.Thus, as for the refractive index of the base resin monomer for light-activated composite resin, it is desirable to use the monomers with refractive indices which are close to that of a filler and change little during polymerization.

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Improvement in shape recovery ratio in Ti-V-Fe-Al alloys for possible application as dental implants was examined.Based on previous results showing the highest recovery ratio in Ti-11.5V-1.7Fe-3.3Al alloy, four alloys with defferent Al concentrations were examined.In the solution treated specimens, retransformation temperature to mother phase(A_S)shifted towards the lower temperatures with increasing Al concentration.Accodingly, the recovery ratio at 60℃ increased, and 4.0 Al alloy showed the highest ratio of 28.5%.By aging for 3 seconds at 400℃, A_S temperature decreased in about 20 to 30℃, and an increase in recovery ratio was observed.For 4.5 Al alloy, however, other optimum heat treatment conditions were required.Further improvement was obtained by decreasing the plastic bending temperature of aged specimens to -20℃, and especially in 4.0 Al alloy, the recovery ratio was 92% at 60℃.This value was higher that of 3.3 Al reported previously, and this alloy may be suitable as a dental implant.

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