Shika rikogaku zasshi. Journal of the Japan Society for Dental Apparatus and Materials最新文献

NiTi alloy has attracted the most public interest in recent years. This alloy has two unique properties, one is "shape memory effect" and the other is "outstanding elasticity". NiTi wire with the property of outstanding elasticity suggested it could be useful in orthodontics. Recently new NiTi alloy which had other characteristics of "superelasticity" was developed. In this study, new superelastic NiTi wire was examined to evaluate for use in orthodontics, in tensile and bend tests, compared with stainless steel, Co-Cr alloy and work hardened NiTi wire. The results obtained are as follows: (1) New superelastic NiTi wire showed unique stress-strain curve with a plateau from the strain of 2% to 5%, the unique deformation behavior was caused by stress induced transformation, and returned to almost zero strain as stress was reduced. (2) New superelastic NiTi wire showed an elongation of about 11%. In the cyclic tensile tests to the strain of 8%, new superelastic NiTi wire showed little permanent deformation of 0.5% after 10 cycles. (3) In bend tests, new superelastic NiTi wire showed lower than half load compared with stainless steel and Co-Cr alloy wires. Its permanent deformation was very little after 2 mm deflection. (4) The load-deflection curve of new superelastic NiTi wire showed almost constant load in the wide range of deflection. The results of this study indicate that new superelastic NiTi wire must be considered as a promising candidate for orthodontic arch wire.

The effect of quartz addition was investigated on the sintering processes of powder compacts made from frit and glass powder with quartz powder. The results obtained are summarized as follows. 1) The quartz powder gave some effects on the shrinkage curves and the firing temperature range of frit and glass powder. Pyrex glass powder was more effective on the firing temperature range of the powder compacts with quartz addition comparing with other frits and glass powders. 2) The produced crystal during heat treatment of the powder compacts made from pyrex glass powder with quartz powder were cristobalite. 3) The sintered composite showed larger thermal expansion value by expansion due to the transition of cristobalite followed with the crystallization of cristobalite than that without crystallizing property.

Sintered 316 L stainless steel, made by slip casting, was studied in the present work for its potential use as a medical prosthesis. The physical and mechanical properties were scrutinized to determine characteristics of the specimens. Corrosion tests were conducted in boiling 5% H2SO4. Microstructures of the specimens were examined. The samples were implanted for 31 days in the dorsolateral subcutaneous site of living rats. The results were as follows. The shrinkage during heating varied from 10.3 to 33.0%, the relative density from 0.41 to 0.78, and porosity from 20.4 to 58.2%. Tensile strength varied from 2.3 to 24.6 kg/mm2, yield strength from 2.8 to 11.6 kg/mm2, elastic modulus from 1 075 to 7 400 kg/mm2, elongation from 9.1 to 19%, hardness of Brinell scale from 7.5 to 53.1. Mechanical properties as mentioned above decreased with increasing porosity. Pore size distribution varied 4.4 to 44 mu. Both Si and ferrite, or either of the two were observed in the matrix of austenite. Corrosion resistance were effected greatly by the porosity. Blood vessels, fibroblasts, fibrous tissues were found surrounding the sintered specimens and in the interior pores. No degeneration or necrosis were noted. Based on the tentative findings of the present studies, I can say that sintered stainless steel have a potential for medical application.

In order to investigate the adhesiveness of polysulfide rubber impression material to dental metals, we performed the tension test on the sample specimens which had been prepared by injecting the impression material into the gap between opposite metal surfaces finished brightly, thereafter observed the fractured surfaces. Pure metals decreased their adhesive strength to the impression material in order of Au, Pd greater than Ag greater than Cu. Some noble metal alloys containing gold and palladium in a large amount showed the good adhesiveness. In clinical using of 14 carat gold and gold-palladium-silver alloys for core metal, it should be noticed that polysulfide rubber adheres tightly to these alloys. Adhesive strength of copper was not so great comparing with noble metals, therefore the surface of copper tray should be roughned by emery paper above #500, aiming the mechanical bonding forth to increase. The surface of many metals which had left in regulated atmosphere for many hours showed the tendency to decrease their adhesiveness to the impression material. This tendency was not recognized on the metals which had appeared the failure of adhesion bond on the bright finished surfaces.

We measured the dimensional change of mold cavity in casting ring and casting accuracy for inlay type casting using two kinds of lining materials in various conditions. These lining materials were asbestos ribbon and ceramic fiber. In the comparison of cushion ability for the expansion of investment in casting ring of these two lining materials, following results were obtained. 1. Compressibility of ceramic fiber was twice as much as asbestos. And, two sheets of ceramic fiber ribbons had enough ability for free expansion of investment in casting ring. 2. More than two sheets of asbestos ribbons in dry state had the ability of compensation for casting shrinkage in heating process. 3. Asbestos ribbon in wet state made a setting expansion of investment larger, but had not any ability of cushion for heating expansion of investment. 4. If the cushion ability of lining materials was not enough, the mold cavity shrank. The order of this shrinking inclination were no lining material state, two sheets, one sheet of wet asbestos, and one sheet of dry asbestos. 5. This shrinking inclination of smaller cavity was greater than that of larger cavity. That meant that the larger thickness of investment in ring made this shrinking inclination greater. 6. In case of without mold cavity, the heating expansion of the investment toward the casting ring were same value at any position in casting ring.

Thermal behavior of MgNH4PO4.6H2O was investigated by means of TG-DTA and X-ray diffraction. Two endothermic peaks (90 degrees C and 230 degrees C) and a exothermic peak (660 degrees C) were observed in a micro-DTA curve. Weight loss occurred at two stages corresponding to the two endothermic peaks. Values of weight loss were about 38% and 53%, respectively, at the end of each stage. These values were nearly equal to theoretical weight losses in the formation of Mg2P2O7 from MgNH4PO4.6H2O via MgNH4PO4.H2O. The intermediate, MgNH4PO4.H2O was identified by X-ray diffraction. The second weight loss continued till about 600 degrees C. The product during the second stage was amorphous and Mg2P2O7 began to crystallize above about 600 degrees C. The exothermic peak was thought to correspond to the crystallization. On the other hand, the first endothermic peak separated into two peaks in a macro-DTA curve. The first corresponded to removal of crystal water from MgNH4PO4.6H2O and the second to evaporation of the condensed water. Moreover the exothermic peak also separated into two peaks and the peak temperatures lowered. It was considered that the crystallization was affected by the atmosphere.

In low-melting 32 Ni-23 Cu-25 Mn alloy, the structure change and the segregation distribution were investigated in optical microscopy. The use of air-vent system to casting specimen had a notable effect to morphology and grain-size distribution, but the segregation showed the same tendency as the air-cooled specimen without air-vent system, except Cu segregated in B-grain less than in C-grain.

Bovine enamels cleaned with citric acid and FeCl3 which had been brushed or ground were joined with PMMA rods with the 4-META/MMA-TBB cement. Their tensile adhesive strength was measured after post-treatments. Stable adhesive strength such as 6.2 MPa was obtained on an enamel which was brushed and washed with an aqueous solution of 10% citric acid-3% FeCl3 for 30 sec. even after a 60 times percolation test between 4 degrees C and 60 degrees C. It is adequate to clinics. The value increased to 16.1 MPa on ground enamel. These results suggest that phosphoric acid etching, essential nowadays, is not necessary for good adhesion to enamel. Monomers with both hydrophobic and hydrophilic groups like 4-META possess affinity with tooth substrates and promote the infiltration of cements into the enamel. The infiltrated monomers polymerized in situ and strong adhesion with the enamel took place. Comparison of the tag length formed in the enamel by cements, MMA-TBB, HNPM/MMA-TBB, Phenyl-P/MMA-TBB and 4-META/MMA-TBB supports this consideration.

Reaction process in the equimolar mixtures of MgO-MgNH4PO4.6H2O and MgO-NH4H2PO4 were investigated by TG-DTA and X-ray diffraction. In the MgO-MgNH4PO4.6H2O system, MgNH4PO4.6H2O was changed by heating in the following way. The formation of MgNH4PO4.H2O by dehydration about 100 degrees C and of amorphous Mg2P2O7 by dehydration and removal of NH3 above 200 degrees C and the crystallization of Mg2P2O7 above 600 degrees C. A part of the amorphous Mg2P2O7 reacted with MgO to form Mg3(PO4)2 above 600 degrees C. The crystallized Mg2P2O7 also reacted with MgO to form Mg3(PO4)2 at higher temperature. In the MgO-NH4H2PO4 system, MgNH4PO4.H2O was formed by the reaction between them, which was corresponded to an exothermic peak about 140 degrees C in the DTA curve. MgNH4PO4.H2O, an unknown phase Y and an amorphous phase were formed at 200 degrees C. The crystalline phases almost disappeared and another unknown phase X appeared at 300 degrees C. The phase X also disappeared and Mg(PO3)2 appeared at 400 degrees C. In the TG-DTA curve for this system, an exothermic peak, which was corresponded to crystallization of Mg(PO3)2, was observed about 550 degrees C and the decomposition of NH4H2PO4 ceased after the crystallization. Mg(PO3)2 reacted with MgO to form Mg2P2O7 at higher temperature.

Scanning electron microscopic studies on dentine surface cleaned with a mixture of citric acid and ferric chloride, fractured surfaces parallel to the tubules of dentine and dentine with the cured adhesive and the partially demineralized fractured surfaces, tensile fractured surface of the joint on the dentine and cured adhesive resin tags impregnated in tubules were carried out to clarify the adhesion mechanism. Infiltration of monomers into dentine is more important to get good adhesion with dentine than the interlocking at dentinal tubules due to impregnated resin. Monomers with both hydrophobic and hydrophilic groups like 4-META promote the monomer infiltration. The infiltrated and cured adhesive layer in dentine is observed at the subsurface dentine zone. This zone has excellent resistance against acid demineralization.