To elucidate the radical-scavenging effects of vitamin E, we studied the polymerization of methyl methacrylate in the presence of vitamine E and its related compounds(BHT:2, 6-Di-tert-butyl-4-methylphenol and phenol)by BPO at 70℃ using DSC.Induction period and initial rate of polymerization(IRP)were determined from time-conversion curves derived from DSC thermogram.The induction period of phenolic compounds in the BPO system was dependent on the concentration.As the concentration increased, the induction period increased.Its values decreased in the order:BHT>phenol>vitamin E.Compared to phenol, IRP of vitamin E markedly decreased as the concentration increased.It was concluded from this that vitamin E is a retarder.The IRP of BHT was not changed at the range of 0-0.1mole%, indicating that BHT was an efficient inhibitor.In the azobisisobutyronitrile(AIBN)system, the induction period decreased in the order:vitamin E>BHT>phenol.Vitamin E interacted strongly with radicals generated by AIBN.

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Four different cement powders with varied indium trifluorides concentrations(0, 1, 2 and 3wt%)were made by adding indium trifluoride to tetracalcium phosphate powders.The experimental cement powders were refired at 1, 400℃ for two hours in air, then mixed with a 9.9wt% citric-39.5wt% malic acid aqueous solution at powder-liquid ratios of 1.0, 1.2 and 1.4(g/g).Setting time, compressive strength and disintegration of the experimental cements were determined according to the procedures outlined in ANSI/ADA Specification No.61 for zinc polycarboxylate cement.The setting time of the experimental cements at each concentration of indium trifluorides significantly decreased with increases in the powder-liquid ratio.The compressive strength of the experimental cements at each concentration of indium trifluorides significantly increased with increases in the powder-liquid ratio.The amount of disintegration decreased significantly as the powder-liquid ratio increased.

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To determine the effects of various dimethacrylate monomers on setting characteristics of composite resins, seven types of UDMA・EDMA based photo cure composite resins were investigated.The base monomer used in this study was a 50/50% mixture in molar ratio of various ethyleneglycol dimethacrylates and urethane dimethacrylate(UDMA).And silicafiller particles(1.9μm), surface treated with a silane coupling agent(3.26% γ-MPTMS), were added to the base monomer in a weight ratio of 65%.The results obtained were as follows.When the repeating structural unit(n)of〓OCH_2CH_2〓_n of ethyleneglycol increased from 1 to 23, Knoop hardness and polymerization shrinkage of the composite resins examined decreased from 62.1 to 6.56 and from 7.831% to 1.478%, respectively.Inversely, unreacted substance increased from 1.21% to 5.51% with increase of n.

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Seven types of UDMA・EDMA based photo-cure composite resins were investigated to determine the effects of the monomer structure on physical properties and dynamic viscoelastic properties.The base monomers used were mixtures of various ethyleneglycol dimethacrylates and urethane dimethacrylate(UDMA)in a molar ratio of 50/50%.And 65wt% silanized silica-fillers(1.9μm)were added to the base monomers.The results obtained were as follows.Dynamic shear modulus(G')of seven composite resins decreased with increasing temperature.As the number(n)of〓OCH_2CH_2〓_n chain of the ethyleneglycol dimethacrylates increased from 1 to 23, the G' at 37℃ decreased from 5.40GPa to 0.36GPa.The thermal expansion coefficient and water sorption increased inversely from 36.5×10^-6℃ to 112.0×10^-6/℃(37〜80℃)and from 0.50mg/cm^2 to 2.54mg/cm^2(30days after start of storage in water)with increases of n, respectively.

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The function of a nonionic surfactant, poly(ethylene glycol)p-isooctylphenyl ether(TX)in bonding to dentin conditioned with 10-3 for 10s was studied to understand the bonding mechanism to dentin.When the conditioned dentin was immersed in 0.02% TX for 3min after a water rinse and dry, the bond strength of MMA-TBB resin increased to 13.8MPa from 8.0MPa.This procedure was further simplified by direct immersion in 0.02% TX for 40s and equal bond strength(12.4MPa)was obtained.Hybridized dentin was identified by SEM examination in both cases.It was concluded that monomer permeability of substrates is as important as the diffusibility of monomers in preparing hybridized dentin that could unify dentin and resins.TX enhances the impregnation of MMA by improving the monomer permeability of dentin.

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When orthodontic metal brackets are bonded to teeth with light-curing resins, the light does not directly reach the resin under brackets.Therefore, there is concern about the polymerization of resins and bond strength.In this study, the influences of irradiation time and irradiation direction was investigated on the degree of conversion(DC)of light-curing resins under the brackets by using FT-IR method.In the irradiation for 10sec., the resins showed uneven DC.Prolonged irradiation increased DC of resins and constant DC was observed throughout the resins.DC reached 70% in the irradiation for 40sec., but it did not increase any more with the longer irradiation.Therefore, this indicates that the uppermost DC in this study is approximately 70%.

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When Au-Ag-Pd alloys contacted electrically with stainless steel, such as type 447J1 and 316L, were immersed in 0.9% NaCl solution at 37℃ for seven days, amounts of ions released from Au-Ag-Pd alloys and stainless steel increased compared with that after a single immersion.The resting potential of each was changed with the immersion time.Au-Ag-Pd Alloys showed more noble potentials initially.However, the potentials of stainless steel increased gradually and were higher than those of the Au-Ag-Pd alloys after a few hours.Mixed potentials initially stayed around the corrosion area of stainless steel with higher current density compared to that with single potential.After potentials were reversed, the mixed potential moved into the corrosion area of Au-Ag-Pd alloys with higher current density.Therefore, the stainless steel initially and Au-Ag-Pd alloys after a few hours were so easy to corrode that both the nobel and base alloys showed accelerated corrosion under these Conditions.

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By combining information from X-ray transparency and from molten titanium flow, the casting process in a U-type cavity simulating crown section was investigated under several conditions, such as type of casting machine or sprue diameter.Despite the machine type, centrifugal(CT)or two-chamber pressure(PR)machine, jet flow and F type filling were observed in the occlusal area.The flow pattern in the axial area, however, was controlled by the main body force of each casting machine;it was the B type for PR and the F type for CT.Major factors related to internal defects were sprue diameter for PR and sprue-attachment position and angle for CT.

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The controlled mother alloys, 30Pd-15Cu-55Ag(AP), 12Au-20Pd-15Cu-53Ag(APG)containing 0.03% Ir and seven kinds of alloys adding total amount of 2% Zn and/or Sn and/or In to AP and APG alloys which composition were arranged according to special cubic type in simplex lattice designs for multicomponent systems(3 components), were prepared and cast.After softening and hardening heat treatment, the mechanical properties and apparent specific gravity of the specimens were measured.The alloys adding 2% Zn to AP and APG, appeared to have a minimum tensile strength, Vickers hardness number, elastic limit and proof strength(value of strength characteristics)and maximal elongation.The alloys with 2% Sn appeared to have the maximal strength characteristics, or to show no significant difference compared with the maximum values.In(indium)had a tendency to decrease strength and elongation.No significant correlation was found between the specific gravity of as-cast specimens and value of strength characteristics of heat-treated specimens.The result indicates that the best additive for AP and APG is less than 2% Sn or 1% Sn and Zn.

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Titanium-nickel alloy(Ti-Ni alloy)is known to possess super-elasticity and shape memory properties, and the recent focus has also produced a hi-damping alloy.This study investigated the damping capacity of the super-elastic Ti-Ni alloy wire, which is used in orthdontics, in comparison with stainless steel wire.The damping curve of the Ti-Ni alloy wire was found to decrease abruptly, while that of the stainless steel wire decreased gradually.It was additionally shown from the specific damping capacity(SDC)that the super-elastic Ti-Ni alloy wire possesses elevated damping capacity compared with that of the stainless steel wire.

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Chronological change in the properties of composites was measured up to 500 days after immersion in food-simulating solutions, such as 20% alcohol solution, citric acid solution, salad oil and distilled water.The absorption rate of composites was almost same in aqueous solutions, that is, 20% alcohol solution, citric acid solution and distilleds water.The absorption rate in salad oil was 1/3-1/4 lower than those in aqlueous solutions.By immersion in these solutions, the resin matrix of composites was plasticized by the solutions absorbed, and the flexural strength of composites after 100 days on composites was prone to be increased especially in salad oil.Thereafter, the mechanical properties of composites were decreased by the debonding of the filler/matrix interface in aqueous solutions.

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Various heat treatments were carried out on dental Au-Ag-Pd-Cu alloy.Tensile tests and dynamic fracture toughness tests were then carried out on the heat-treated alloys.The influence of heat-treatment conditions on tensile and impact fracture characteristics were then investigated based on the test results.Tensile strength and 0.2% proof stress increased with increased solutionizing temperature.Tensile strength and 0.2% proof stress increased with increased aging temperature in aged materials.On the contrary, elongation decreased with increased solutionizing temperature in as-solutionized materials.Dynamic fracture toughness value tended to increase with increased solutionizing temperature except in some cases similar to the trend in strength values.Increased strength contributes more markedly to dynamic fracture toughness compared to the loss due to decreased ductility.The dynamic fracture toughness value was greater in as-solutionized materials than in aged materials.Heat-treatment with a solutionizing temperature of 1073K was judged to provide superior results when strength, toughness and ductility were taken into account.In as-solutionized materials, the heat treatment process where air cooling was performed after solutionizing was superior because the cooling process was more convenient and aging process can be omitted.

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