Shika zairyo, kikai = Journal of the Japanese Society for Dental Materials and Devices最新文献

Effect of adhesion promoting monomers dissolved in photocurable bonding agents on adhesion to ground dentin was investigated. They were MDP, Phosmer-M and 4-MET. The effect of those monomers was compared with that of Phenyl-P. The bonding agents contained campherquinone (CQ) as a photosensitizer, N-phenylglycine (NPG) as a reducing agent and TEGDMA as a base monomer. Phenyl-P was the best adhesion promoting monomer among those studied monomers. MDP could not polymerize well enough to give good bond strength. Phosmer-M could permeate through the smeared layer but could not make a stable resin reinforced dentin. 4-MET did not permeate through the smeared layer and did not adhere to ground dentin.

A new apatite-collagen complex was prepared in calcium beta-glycerophosphate solutions at pH 8.50. For this preparation, reconstituted type I collagen was cross-linked with phosvitin in the presence of alkaline phosphatase by use of a cross-linking agent of dimethyl suberimidate. After two weeks of immersion in daily-renewed solution of calcium beta-glycerophosphate, the complex contained apatite approximately two times the modified collagen in weight. When viewed in a scanning electron microscope, needle-like crystals precipitated densely on the collagen fibrils. However, in some portion of the complex, dot-like precipitate was observed as well. X-ray diffraction and IR analyses of the complex suggested that the apatite precipitated on the collagen fibrils was very similar to bone mineral in two aspects, crystallinity and carbonate content.

The water sorption and desorption, and the diffusion coefficients of the water sorption and desorption were studied on the experimental composite resins with various filler contents in both chemically-cured and light-cured type. As the filler content increased, the rate of the water sorption and desorption on the composites decreased. And these properties associated with the prediction obtained from the law of mixture. The filler did not absorb water, so the effect of the filler content on the diffusion coefficients of the water sorption was to be associated with of the law of mixture. However, in the diffusion coefficients of the water desorption the effect of filler content could not be proved to be associated with the law of mixture. The diffusion coefficients of the water desorption were over 2 times larger than the those of the water sorption.

To obtain inlay, crown and bridge types of titanium castings with sufficient size accuracy, zirconia investments with 10 mol % calcia were studied for their setting expansion, thermal expansion, total expansion, casting shrinkage compensation deficiency on fabrication method, particle size of zirconia, calcia and mixing liquid. Addition of calcia caused the change from contraction to expansion in setting and the additional thermal expansion at 900-1,200 degrees C. The choice of calcia and mixing liquid makes great influence on setting expansion, which is grouped into saturation type and delayed expansion type. By the use of the saturation type, total expansion could be controlled in the range of -2-(+)3%. Titanium castings of inlay, crown, bridge types with the values -2-(+)2% of casting shrinkage compensation deficiency could be successfully obtained. The casting shrinkage of titanium was estimated as 1.8-2%. The castings have the surface with a metallic brilliance as cast.

A new time-saving method has been developed to produce artificial crowns without using the casting process. Plastic mixtures of gallium and other metal particles are kneaded into desired shape and then heated for hardening. By this method, the time required for hardening and producing restorative materials has been shortened greatly. In the present experiment, gallium was triturated with powdered gold, silver and copper to make binary alloy samples. The dimensional change was measured between heat treatment. After heat treatment, the test piece was examined for compressive strength, compressive shrinkage, hardness, tarnishing and difference in phase. Non-heated and heated alloy specimens (Au-Ga, Ag-Ga, Cu-Ga) expanded to form the new phase. The ability of Au-Ga samples to bear compressive strength, when heated at 300 degrees C or more (AuGa2----AuGa), became 2.6 times greater than that of non-heat-treated specimens. The compressive strength of Ag-Ga samples dropped briefly at 350 degrees C (Ag0.72Ga0.28----Ag3Ga) but increased at 450 degrees C (Ag3Ga----AgGa). The strength of Cu-Ga pieces fell by half at 475 degrees C and upward (CuGa2----unknown phase). A compression test showed that the contraction percentage of Au and Ag specimens became large as a result of heat treatment, while that of Cu alloys remained almost unchanged. The results of a hardness test (HV) were comparable to those of the compressive strength test. The Au-Ga alloys increased in hardness after high-temperature treatment. In the Ag-Ga alloys, hardness declined at 350 degrees C and increased at 450 degrees C. There was no difference in hardness between Cu specimens after heat treatment and those allowed to stand at room temperature. A tarnishing test revealed that Au-Ga samples turned slightly yellowish. In the case of Ag-Ga samples, the reflectivity Y (%) dipped slightly but discoloration was not recognizable. However, the Cu-Ga samples which were heated at temperatures of up to 280 degrees C showed a slight drop in reflectivity, but those heated at temperatures higher than 280 degrees C decreased to 50-66% in reflectivity and turned black.

The goal of this study was to test the influence of the type and oxidation treatment of dental casting alloys on the tensile bond strength of luting cements. Also, the influence of film thickness of luting cements on the tensile bond strength of different dental casting alloys was examined. Four different luting cements (zinc phosphate, polycarboxylate, glass ionomer and adhesive resin cements) and four different dental casting alloys (Au-Ag-Cu, Ag-Pd, hardened Ag-Pd and Ni-Cr alloys) were used. Cylindrical alloy rods for the tensile bond strength test were casted, and then, top surfaces of the rods were cemented with each luting cement to the bottom surfaces of other rods, using the film thickness adjustment apparatus. The film thickness of luting cement was adjusted to 20, 30, 50, 75 or 100 microns. The tensile bond strengths of each cement to different casting alloys at each film thickness were measured one day after the rods had been cemented. The tensile bond strength of the zinc phosphate cement could not be determined in this study due to the separation of the alloy rods cemented with the zinc phosphate cement in water before the tensile test. The tensile bond strength to the adhesive resin cement to any alloy showed the greatest strength; however, that of the glass ionomer cement to any alloy was the lowest strength among the cements examined. The Ni-Cr alloy had the highest bond strength of any luting cement, compared to other alloys. The tensile bond strengths of luting cements significantly decreased with the increase in film thickness of cement layer. The adhesive resin cement had the greatest bond strength, and the glass ionomer cement was the lowest bond strength at any film thickness. The oxidation treatment significantly increased the bond strength of the adhesive resin cement to both Au-Ag-Cu and Ag-Pd alloys. The tensile bond strength of the adhesive resin cement was most dependent upon the film thickness of cement layer, and that of the polycarboxylate cement was least dependent upon the film thickness of cement layer among the cements examined. In addition, the oxidation treatment for precious alloys could be a factor contributing to the increase in the bond strength of the adhesive resin cement.

Adhesion between dentin and MMA resin was investigated using chemically activated initiator system consisting of 1,3,5-trimethyl-2-thiobarbituric acid, cupric salt, chloride ion, and tert.-butyl peroxymaleic acid (MA) with carboxyl group which usually has affinity to tooth. The adhesive strength of the MMA/PMMA resin to bovine dentin increased significantly to 8-10 MPa by addition of MA, while the adhesive strength was 4 MPa without MA. When the bonding broke at higher than 7 MPa, the adhesive resin layer usually fractured cohesively and the interfacial fracture did not occur. The bond strength obtained in this experiment was comparable to that obtained with MMA resin using TBBO and ferric ion initiator system which is known as the best initiator system for dentin available.

A preliminary CAD system to design the inner and outer shape of crown prosthesis was developed using the data of 7 abutment and molar measured in the previous paper. The gingival and marginal line in the abutment tooth could be recognized more certainly by the "GIN-MAGN" program, and the three dimensional data of tooth crown above the gingival line could be output and saved. To prepare the data base of the occlusal surface of tooth crown, the data of tooth crown above the gingival line of 7 molar were also output by the "GIN-M" program. The data around the toothneck were excluded with an arbitrary height above the gingival line in order to connect smoothly with the margin line of the abutment tooth. The tooth crown data were set up on the abutment data by means of the program "AB-CR-E". In the present system, even though the occlusal condition with the antagonistic tooth could not be taken into account, the CAD procedure to set up a tooth crown with an arbitrary size on the arbitrary position of abutment tooth could be accomplished, and the toothneck data of crown were connected with the margin of abutment tooth.

The fatigue characteristics of a zinc phosphate cement were examined. Using a split mould made of stainless steel, 12 mm x phi 6 mm column shape specimens were prepared. Fatigue tests were done by loading partially repeated pulsating diametrical tensile stress of 1-20 Hz, minimum stress was 0.2 MPa (2.0 kgf/cm2) and maximum stress was 3.5-5.4 MPa (36-55 kgf/cm2). During testing, the specimen was kept under distilled water. The existence of a fatigue was confirmed and there were marked signs of fatigue on the fracture surface. The relation between maximum stress and the number of cycles to fracture (S-N diagram) was obtained. Therefore the following equation and fatigue parameter (n) were deduced. logS + 0.0775.logN = 0.8931 n = 12.9 The fatigue characteristics depended on the frequency, that is, a time to fracture was shorter at the loading frequency of 20 Hz than that of 1 Hz.

Mechanical properties of heat curing acrylic resin obtained by polymerization for long period of heating at a temperature lower than conventional temperatures were examined. The mechanical properties of the resin were lower than those of the resin cured at 100 degrees C. The results of high performance liquid chromatography and differential scanning calorimetry suggested that the poor mechanical properties were due to significant amounts of residue monomer and benzoyl peroxide in the resin, but is not to changes molecular weight.