This study investigated the effect of Phenyl-P dissolved in 30% HEMA primer on the restoration of shrunken demineralized dentin and improving the monomer permeability.
Light cure resin was bonded to demineralized dentin treated with primers. The priming periods required for an aqueous solution of 30% HEMA could be decreased from 10 min to 1 min by dissolving 1% Phenyl-P in the solution. Phenyl-P was effective for restoring the collapse demineralized dentin in shorter periods. Intact dentin contiguous with the etched dentin was demineralized by Phenyl-P in primer, which made the hybridized dentin layer thicker than the previously demineralized dentin layer.

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Since the denture base absords with use, various deodorant and cleansing preparations are on the market. This absorption of smell is caused by rotting of food residue, so that it may be prevented to some extent by providing a bactericidal property in the resin base. In this study, we examined whether acrylic resin could exhibit bactericidal activity by the oligodynamic action of silver. We evaluated changes in the color, water absorption, solubility and transvers deflection of the denture base resin by the addition of silver powder. Concerning the oligodynamic action, no inhibition zone was observed without the addition of silver powder, but inhibition zones of 0.8-2.4 mm, 1.3-3.3 mm, and 2.1-4.0 mm (4.2 mm with standerd silver) were observed with the addition of silver powder to resin powder at 5%, 10% and 20% respectively. Concerning color changes of the acrylic resin with the addition of silver, the color difference was greater at a higher silver content. The color difference was smaller in dark pink resin than in clear resin. The water absorption and solubility decreased with the increase in the percentage of silver. The transverse deflection also decreased with an increasing percentage of silver.

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To improve the hydrolytic stability of photo cure composite resin, 1, 2-dimethacryloyloxy benzene (DMB) was synthesized. After adding DMB to urethane dimethacrylate (UDMA), the effect on the mechanical properties of the copolymers and photo cure composite resin was investigated. The bending strength of the copolymer with added DMB did not decrease, even though the specimen was immersed in water for 30 days at 60℃. This is due to the fact that the water absorption of the copolymer was decreased by the addition of DMB. However, the bending strength of composite resin was decreased by water absorption. This decrease in the bending strength by the addition of DMB to the matrix resin was less than that by the addition of TEGDMA. We conclude that the addition of DMB to photo cure composite resin could improve hydrolytic stability.

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In some commercial acrylic denture base resins, alkylmethacrylates, such as ethylmethacrylate or butylmethacrylate, have been added to methylmethacrylate to control the dough time.This study invstigated the effect of adding alkylmethacrylates on the viscoelastic properties and the impact strength.Test specimens were prepared both by the conventional heat-curing method and by heat-pressure welding of polymers.The storage modulus and loss modulus in the temperature range from 20 to 140℃ were measured, and the glass transition temperature(T_g)was determined.Furthermore, the values of impact energy were measured using an izod impact test at a temperature of 23℃.Increasing the amount of ethylmethacrylate or butylmethacrylate added to methylmethacrylate caused a decrease in the storage modulus, the loss modulus and the impact strength.In particular, the impact strength decreased markedly.These results suggest that it is preferable to reduce the volume of alkylmethacrylates added to control the dough time of denture base resin.

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To develop fluoride-releasing dental materials, three kinds of fluoride-releasing phosphazene monomers were synthesized and analyzed.Using hexafluorocyclotriphosphazene(P_3N_3F_6), three kinds of P_3N_3(F)_<1-3>(EMA)_<5-3> were synthesized by replacing 3〜5 of fluoride with HEMA.On IR, NMR and elemental analysis, all synthesized monomers were within expectation.Their refractive index were 1.4662〜1.4718 and viscosity were 1.3〜1.8Pa・s.Then, 30wt% of synthesized monomers were mixed with MMA and light-cured.Polymers were produced by mixing with PMMA.Amounts of fluoride released and the transverse strength were measured after a period of immersion in water at 37℃.Amounts of fluoride released by the three kinds of polymers were decreased with changes in the immersion period.After 1 day and 360 days immersion in water, amounts of floride released were 2.0〜3.3μg/ml and 0.2〜0.8μg/ml respectively.Transverse strength after 360 days immersion in water was 74.0〜76.0MPa.Amounts of fluoride released and transverse strength showed a tendency to decrease with increases in the immersion period when commercial sealant was used as a control.

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A new resin-composite was prepared using a highly transparent filler(r（Optoligh).The resin-composite showed good photopolymerization and the cured composite showed high transmittance in the range of 400-800nm wavelength as well as good mechanical properties compared with that of conventional fillers such as fused silica and ground quartz.

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Dissolution behavior of sintered carbonate containing apatites was investigated in 10mM acetic acid solutions with the pH adjusted to 5.00 at 37℃.The solution compositions obtained were analyzed using chemical potential plots.Analysis of chemical potential plots suggested that specimens, which were obtained by sintering apatite containing 11.8wt% carbonate at temperatures between 600 and 850℃, were as soluble as deproteinated bovine bone apatite and much more soluble than sintered hydroxyapatite.With sintered hydroxyapatite, the solution composition stopped moving at a position slightly below the solubility line of hydroxyapatite after 2〜3 days of dissolution, indicating that the solution composition became equilibrium with the solid phase hydroxyapatite.Closer examination of the chemical potential plots of sintered apatite containing carbonate also suggested that the specimens were as soluble as octacalcium phosphate and/of β-tricalcium phosphate, since their solution compositions moved close to or on the solubility lines of those calcium phosphates.From these findings, it is suggested that sintered carbonate apatites, when implanted as bone substitute materials, would resorb, since bioresorption associated with osteoclasts could be regarded as physicochemical dissolution.

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Thiirane monomers containing a long alkylene chain, 9, 10-epithiodecyl methacrylate(EP8MA)and 10, 11-epithioundecyl methacrylate(EP9MA), were synthesized to provide adhesive bonding promoters for precious metal alloys.Three kinds of adherends such as gold alloy, gold-silver-palladium alloy and silver alloy were polished to a mirror-like finish.These surfaces were then covered with a solution of thiirane and allowed to stand for one day.The surfaces were washed when the concentration was high(1mol%).Two alloy specimens were butt-jointed together with MMA-PMMA resin and tensile bond strengths were measured after thermal cyclings.The effect of the chain length of alkylene moiety in thiirane on the adhesion of resin to precious metal alloys was evaluated by comparing bond strengths obtained for EP8MA or EP9MA with those of their homologues.It was proven that thiiranes with a long alkylene chain, EP8MA and EP9MA, provided stable adhesion under a wide variety of test conditions.

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To clarify the biocompatibility of titanium alloys, the dissolution of these alloys immersed in amino acid solutions and the mutagenicity of the released substances from the alloys were studied.Six hundred mg of each powder of Ti-6Al-4V, Ti-5Al-2.5Fe, Ti-5Al-3Mo-4Zr and Ni-Ti was immersed in 5ml of 10　^-1　M cysteine or glutathione solution at 37℃ for 2 weeks.The dissolved metals in the solutions were analyzed by an atomic absorption spectrophotometer or inductively coupled plasma emission spectrometer(ICP).Leaching of Ti, Al, V, Fe and Ni from the alloys was observed.The average volumes of Ti, Al and V from Ti-6Al-4V alloy detected in the glutathione solution were 31.6, 400 and 79.6pg/mg of alloy/days, respectively.There was no significant increase in the frequency of the unscheduled DNA synthesis in HeLa cells exposed to the two extracts observed.A small but significant increase in the exchange of sister chromatides in V79 cells treated with glutathione extracts of a Ti-5Al-3Mo-4Zr alloy could be demonstrated.

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The effects of metals and the surface roughness of metal on mode I fracture toughness at opaque porcelain/metal interface were investigated using an An-Pt precious alloy, two Au-Pd and Pd semiprecious alloys and a Ni-Cr nonprecious alloy as metal. The variations in surface roughness were obtained by various methods of fusing porcelain to the surface of metals, such as sandblasting (50 and 125 μm), emery paper (#40) and retension beads (100 μm). The major findings were as follows.In all metals used, it was found that the interfacial fracture toughness at the process of crack propagation was constant. The value of interfacial fracture toughness of the nonprecious alloy, G_IC=18.5 J/m², was about 14 to 20% larger than those of three other alloys used. On the effect of surface roughness, it was found that larger quantities of foamy opaque porcelain remained on the metal surface as the surface roughness increased.The interfacial fracture toughness after emery paper treatment was only about 10% greater than that of sandblast treatment, however, that after retention bead treatment showed a three-fold increase.Therefore, the retention bead treatment was very effective. It was recognezed that the method of determining mode I interfacial fracture toughness used in this paper was more effective for evaluating the interfacial property of dental materials.

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In this study, the effects of heat treatment on the fatigue strength of dental gold-silver-palladium alloy casting was investigated. Dumbbell-shaped specimens measuring 2 mmφ×14 mm at the parallel portion were cast and heat-treated according to the manufacture's instructions. Tensile and fatigue tests were performed using a universal testing machine with an extensometer. The fatigue strength at 10⁵ cyclic load of sine wave at a frequency of 5 Hz was determined by the staircase method. The fatigue strength of the specimen as cast, the softened specimen and the hardened specimen were 321.5, 288.8 and 320.8 MPa, respectively; the ratios of fatigue strength to tensile strength were 0.546, 0.568 and 0.428, respectively. From the increase in strain measured during fatigue test, fatigue crack initiation and growth was observed. These results suggest that heat treatment of this alloy according to the manufacture's instruction did not improve the fatigue strength.

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This study investigated the effect of newly synthesized N-acryloyl aspartic acid(N-AAsp)on the formation of a hybrid layer and the promotion of dentin adhesion.Bovine dentin surfaces were treated for 60seconds with an experimental self-etching primer containing N-AAsp(20wt% in water)and air-dried(unrinsed group).As a control, specimens were rinsed with water to remove N-AAsp prior to air-drying(rinsed group).The resin bonded specimens were prepared and the bond strength was measured.The resin-dentin interface was obeserved by SEM after the bonded specimen was immersed in NaOCl solution for 4 hours.The bond strengths were 13.4(3.0)MPa for the unrinsed group and 7.0(2.3)MPa for the rinsed group.The structure of the hydrid layer formed in the rinsed group was more porous than that in the unrinsed group.This finding indicates that collagen fibers in unrinsed group prevented the dissolution by NaOCl.These results indicate that N-AAsp facilitates the formation of a tight hybrid layer, thus promoting good adhesion to dentin.

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