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A Comparison with Central and Marginal Regions
Hiroyuki NAKAI, Kazuomi SUZUKI, Hirokazu HASHIMOTO
1985 Volume 4 Issue 2 Pages
125-133,275
Published: December 25, 1985
Released on J-STAGE: February 12, 2009
JOURNAL
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The effect of mercury to alloy ratio on the hardness of high copper amalgam restoration at the margin and center of the amalgam was examined. The hardness of amalgams made from lower mercury to alloy ratio was smaller than that prepared by the manufacture's recommendation. With higher mercury to alloy ratio, the resultant hardness was smaller, and differed from alloy to alloy. Some single compositional high copper amalgams had markedly smaller hardness than others, including low copper amalgams. Regardless of the alloy type and mercury to alloy ratio, the hardness at the margin of the amalgam was apparently smaller than that of the canter. This was more prominent in high copper amalgams.
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Hiroyuki NAKAI, Kazuomi SUZUKI, Hirokazu HASHIMOTO
1985 Volume 4 Issue 2 Pages
134-145,275
Published: December 25, 1985
Released on J-STAGE: February 12, 2009
JOURNAL
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The distribution of hardness was determined in sectioned amalgam restorations prepared with four alloys with different particle shape and copper content, and were condensed into the prepared cavity as in usual clinical practice. The high copper amalgams were apparently harder than the low copper amalgams, the single compositional high copper amalgam being the hardest among them. The hardness of amalgam adjacent to the lateral cavity wall was obviously smaller than that of the center, and the low copper lathe-cut amalgam had an extremely small hardness. The top of the restoration had a remarkably smaller hardness which was especially apparent with single compositional high copper amalgam. Therefore, the hardness at the margin of an restoration was not the same as that of the center but in considerably smaller, regardless of the alloy type used. Accordingly, the mechanical properties of the marginal region of a high copper amalgam restoration is considered not as favorable as expected from the result of commonly used mechanical tests, compared with low copper amalgams.
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Junzo TAKAHASHI, Masayuki OKAZAKI, Hiroshi KIMURA, Yasuhiro FURUTA
1985 Volume 4 Issue 2 Pages
146-152,275
Published: December 25, 1985
Released on J-STAGE: February 12, 2009
JOURNAL
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Rods of Ni-43.5wt% Ti alloy were prepared under various casting conditions. Specimens which were melted in a cordierite crucible and cast in a phosphate-bonded investment mold had less strength and elongation than those melted in a copper crucible and cast in a phosphate-bonded investment mold. All castings exhibited superelasticity at room temperature. The upper limit of recoverable strain was about 1.8%. The cast clasps made of the alloy had good fit to a die, good flexibility, and superelasticity.
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Hiroshi NAKAJIMA
1985 Volume 4 Issue 2 Pages
153-174,276
Published: December 25, 1985
Released on J-STAGE: February 12, 2009
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The oxidation behavior of gold alloys containing small amounts of Sn and/or In was investigated in order to analyze adherence mechanisms in the porcelain-fused-to-metal (PFM) system. Experimental gold alloys (99.5wt%Au-0.5wt%Sn, 99.5wt%Au-0.5wt%In and 99.0wt%Au-0.5wt%Sn-0.5wt%In) were oxidized over an oxygen partial pressure (Po
2) range from 0.016 to 0.8atm and a temperature range from 700 to 900°C, and a commercial PFM alloy (Ceramic Gold) was done at Po
2≤0.2atm.
Both the concentrated amounts of In in Au-In alloy and of Sn and In in Au-Sn-In alloy on each alloy surface after oxidation increased at Po
2<0.2atm by the transition from internal to external oxidation, and nodules consisting of alloy matrix were observed on the oxidized surface. The oxidation behavior of the commercial PFM alloy was similar to that of Au-Sn-In alloy. Indium in the alloy determined the oxidation behavior and surface characteristics.
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Hideaki SHINTANI, Masafumi FUTAGAMI, Aki YUKIHIRO, Junko SATOU, Naoki ...
1985 Volume 4 Issue 2 Pages
175-180,276
Published: December 25, 1985
Released on J-STAGE: February 12, 2009
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The bonding and the extent of microleakage of two types (composite resin type and 4-META type) of adhesive cements were compared with those of conventional cements (zinc phosphate, glass ionomer).
Tensile bond strength of adhesive cements between metal and metal surface was significantly higher than that of conventional cements.
The extent of marginal leakage of Class II (MO) inlay restorations using adhesive cements analyzed by dye-penetration in thermal cycle between 4°C and 60°C bath 2500 times was significantly less than that occurring with conventional cement.
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Judit VARGA, Hideo MATSUMURA, Eiichi MASUHARA, Tsuneo TABATA
1985 Volume 4 Issue 2 Pages
181-190,276
Published: December 25, 1985
Released on J-STAGE: February 12, 2009
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The alloy “ALBABOND E”, consisting mainly of palladium was given various kinds of surface treatment and then adhered with two different adhesive resins. The surface treatments were: mirror-polishing, sand-blasting with alumina, electrolytical etching, Sn plating and for the last step heating once to 400°C. The adhesive used were: 4-META-MMA-TBB type resin and PANAVIA EX. For comparison, an alloy containing only a small percentage of Pd was tested. To examine the adhesive bonding strength it was tested by thermal cycle for a maximum of 2000 times. The samples were dipped for 1-1 minutes in water of 4°C and 60°C alternatively and then the tensile bonding strength was measured. The treatments that were successful were oxidation by heating, Sn plating and Silicoating in this order and out of two adhesives the durability of adhesive bonding strength of 4-META type resin was stronger than that of PANAVIA EX. The electrolytical etching made the surface rough but had no effect to the adhesive bonding strength, which appears to be because the precious metallic components of the alloy are retained in larger quantities on superficial layer.
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Kazuo IDA, Yoshiaki TANI, Sadami TSUTSUMI, Toshihiro TOGAYA, Toshiyuki ...
1985 Volume 4 Issue 2 Pages
191-195,277
Published: December 25, 1985
Released on J-STAGE: February 12, 2009
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A new casting method for titanium revealed that the mechanical properties of pure titanium castings were close to those of gold alloy and more ductile than Ni-Cr or Co-Cr alloy. In this investigation, more than a hundred pure titanium crowns were produced and tested clinically.
The fitness of titanium crowns was slightly inferior to silver-palladium low gold crowns but superior to nickel-chromium crowns. Only one case each of discoloration and occlusal wear of titaoium crowos have been observed in the mouth during a two-year period. The degree of adhesion of plaque to cwnors was about the same among silver-palladium low gold, nickel-chromium and pure titanium.
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Yoshiaki TANI, Katsumi SUZUKI, Toshihiro HAMADA, Shigeki YUASA
1985 Volume 4 Issue 2 Pages
196-200,277
Published: December 25, 1985
Released on J-STAGE: February 12, 2009
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The purpose of the present investigation was to clarify the relationship between polymerization shrinkage of the matrix-monomer of the composite resins and marginal leakage. Eight matrix-monomers differing in polymerization shrinkage (2.7 to 11.4%) were experimentally prepared. Experimental composite resins were made from these monomers filling with 0.2μm spherical silica particles with a constant volume of 54.5 percent. Standardized Class V cavities were prepared on the labial surface of freshly extracted bovine teeth. Before placement of each restoration, the cavities were conditioned and primed with an experimentally prepared bonding agent in which consisted of the Bis-GMA-TGDMA system.
The marginal leakage was evaluated by the scores depending on the depth of the dye penetration. As a result, an S-shaped curve of correlation showed a clear transition at the point of 7 percent of the polymerization shrinkage of the matrix-monomer.
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(6) Physical Properties of Spiro Dimethacrylate Copolymer
Minoru KAWAGUCHI, Tadao FUKUSHIMA, Koji MIYAZAKI, Takashi HORIBE
1985 Volume 4 Issue 2 Pages
201-207,277
Published: December 25, 1985
Released on J-STAGE: March 27, 2009
JOURNAL
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Spiro ring containing dimethacrylate, 3, 9-bis (1, 1-dimethyl-2-methacryloxyethyl) -2, 4, 8, 10-tetraoxaspiro [5, 5] undecane (SPDMA) was synthesized to improve the mechanical and physical properties of dental acrylic resin. Mechanical strength (compressive strength, elastic modulus and Knoop hardness) and water sorption values were measured on SPDMA copolymers (0-30mol%) with methyl methacrylate, and the relationship between concentration or chemical structure of SPDMA and mechanical properties was investigated. To evaluate the relationship between the chemical structure of various methacrylic monomers and the mechanical properties of the copolymers with MMA, the mechanical properties of two aromatic dimethacrylate and one trimethacrylate copolymers were measured.
Compressive strength, elastic modulus and Knoop hardness of SPDMA copolymers increased with increasing concentration of SPDMA, and were similarr to those of copolymers containing aromatic dimethacrylate. Transverse strength of SPDMA copolymers increased with increase in the concentration of SPDMA.
SPDMA copolymers showed slightly higher water sorption values than those of aromatic dimethacrylate copolymers, but lower values than isocyanuric trimethacrylate copolymers.
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I. A Test Method
Seiji BAN, Hisao FUKUI, Sakae MORI, Jiro HASEGAWA
1985 Volume 4 Issue 2 Pages
208-215,278
Published: December 25, 1985
Released on J-STAGE: February 12, 2009
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The pH changes of small amounts of distilled water in contact with the surface of samples of dental luting cement were determined by using a flat combinetion electrode. The results showed that the initial pH value and the neutralization rate of the water in contact with the cement surface decreased with both decreasing amounts of water and the time interval between cement mixing and contact with water. Initial pH value and the neutralization rate for polycarboxylate cement was higher than those for zinc phosphate and glass ionomer cements. This suggests that the water in contact with polycarboxylate cement is rapidly neutralized because of the relatively small release of acid from the cement after initial setting.
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Naoki SATOU, Junko SATOU, Aki YUKIHIRO, Hideaki SHINTANI, Tokio INOUE
1985 Volume 4 Issue 2 Pages
216-222,278
Published: December 25, 1985
Released on J-STAGE: February 12, 2009
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The adherence of a common dental plaque bacterium,
Streptococcus sanguis, to various types of dental cements
in vitro was investigated. Adherent bacteria were counted by using a fluorescent microscope.
The adherence of the cells was found to depend on the incubation time and pH of the incubation medium. Various types of cements differed in their qualities as a substrate for bacterial adhesion. Glass
ionomer, silicate and polycarboxylate cements showed a high degree of cell adhesion, EBA and resin cements were poor substrates for cell adherence. Particular components of cements seem to have different
ability for the adherence of the bacterial cells.
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Seiichiro KONDO, Choji OHKAWA, Takao HANAWA, Toshi SUGAWARA, Mamoru OT ...
1985 Volume 4 Issue 2 Pages
223-230,278
Published: December 25, 1985
Released on J-STAGE: February 12, 2009
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The differences in finished surfaces produced by cutting and grinding instruments were studied with respect to up and down cutting and grinding with a constant load for conventional and microfilled composite resins. Surface roughness obtained with the cutting instrument was considerably dependent upon the particle size of dispersing phase and thereby the heterogeneity of composite resins. Finished surfaces of the up cutting and grinding with both instruments were smoother than those with down cutting and grinding, indicating the infleneces of the direction of tangential cutting and grinding resistances.
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Masaaki NAKAMURA, Koichi IMAI, Hiroshi OSHIMA, Takaya KUDO, Senshiro Y ...
1985 Volume 4 Issue 2 Pages
231-237,279
Published: December 25, 1985
Released on J-STAGE: February 12, 2009
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The in vitro cytctoxicity to HeLa S3 cells of set specimens of five commercially available light-cured composites was examined by the cell colony-forming method for 6 weeks. Both visible and ultraviolet light-cured composites showed moderate to strong cytotoxicity in the early stage of the experiment, followed by rapid disappearance of cytotoxicity. The light-cured composites showed in vitro biological behaviors similar to those of conventional composites, MFR and composites for core use.
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(Part 2) Effect of Addition of Fe, In and Sn on the Deflection at High Temperatures
Nobuo ANDO, Masahiko NAKAYAMA
1985 Volume 4 Issue 2 Pages
238-246,279
Published: December 25, 1985
Released on J-STAGE: February 12, 2009
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Iron, indium and/or tin were added to two mother alloys, 90Au-10Pd and 80Au-20Pt, and 10 kinds of alloys were prepared from each mother alloy. The total amount of the additional elements was 0.75wt%. The deflection at high temperatures (the final deflection after the specimen was heated until 1050°C) and the deflection-beginning temperature (the temperature at which 20μm deflection occurred) were measured, and the effect of the additional elements on these two properties was examined.
The deflection decreased by addition of Fe, In and/or Sn in both alloy system. The deflection-beginning temperature increased by addition of the elements. These results showed that the mechanical properties at high temperatures were improved by addition of Fe, In and/or Sn. The deflection at high temperatures and the deflection-beginning temperature were negatively correlated. Indium appears to increase the deflection in both alloy systems.
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Shinichi UKON, Takaaki KATAYAMA, Tomoji MATSUURA, Koichi AKAGI, Syozo ...
1985 Volume 4 Issue 2 Pages
247-264,280
Published: December 25, 1985
Released on J-STAGE: February 12, 2009
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A new method of deflasking the cast has been developed to recover the denture easily without any deformation or fracture after curing. This new technique utilizes the mechanism of expansion based on hydration of an expansive agent with the main component of CaO. The method using static pressure, and mild splitting of the cast, was clinically applied instead of the conventional dynamic method.
The maximum value of the expansive pressure was about 120Kg/cm
2 in a metal cylinder using the agent with a 40% water content. In dental stone cylindrical models, the pressure was estimated to be 96Kg/cm
2.
No permanent set or fracture of the denture was observed in the experiment using eleven denture models. The maximum value of 6500μstrain during splitting with this agent was within the proportional limit of the resin.
As the expansive pressure is produced gradually, this method is very efficient for removing the denture from the cast in clinical application.
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