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Silver-Palladium-Copper-Gold Alloy
Sakae NAGASAWA, Takamitsu YOSHIDA, Toshihide MIZOGUCHI, Nobuyoshi TERA ...
2003 Volume 22 Issue 3 Pages
227-243
Published: 2003
Released on J-STAGE: February 12, 2009
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Ag-Pd-Cu-Au alloy was subjected to a Thermo-Mechanical Analyzer to investigate high temperature properties up to its liquidus temperature. Microstructural examination and elemental analysis with EPMA were also conducted in the solid/liquid mixture region. The following conclusions were obtained. (1) The solidus temperature was 838.3±2.52°C and 957.7±1.53°C for the liquidus point. (2) Thermal expansion coefficients were 1.39±0.08% at the solidus, 2.338±0.13% at the liquidus, and the melting expansion coefficient was 0.932±0.058%. (3) The expansion during melting was controlled by a small amount of pressure such as 1/100 of the air pressure, therefore the fit accuracy of castings is suggested not to be influenced by the solidification shrinkage. (4) Although the softening heat treatment and casting exhibited an influence on thermal expansion behavior, casting temperature in addition to post-casting plastic deformation did not show an effect on the thermal expansion. (5) The yield strength at 750°C was reduced down to about 1/400 of that at room temperature, and the modulus of elasticity was about 1/100 of the room temperature value.
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Koichi FUJII, Seiji BAN, John F. McCabe
2003 Volume 22 Issue 3 Pages
244-250
Published: 2003
Released on J-STAGE: February 12, 2009
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The purpose of this study was to evaluate the surface roughness and resistance to toothbrush abrasion of three experimental paint-on composite resins developed for the shade modification of crown and bridge resins. The paint-on resins had less filler volume fraction than restorative composites or the crown and bridge resins and consequently were of low viscosity. The maximum surface roughness (R
max) and the maximum depth loss by abrasion for the paint-on resins following 40, 000 cycles of brushing ranged from 2.45 to 4.07μm and 8.63 to 13.67μm, respectively. R
max values were 37.7-67.5% lower than that for the crown and bridge resin subjected to the same test. Wear depth was 19.9-49.4% lower than for the crown and bridge resin. These results suggest that the paint-on resins are expected to have adequate resistance to toothbrush abrasion and may therefore be suitable for clinical use.
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Gaku MURAOKA, Hidekazu TAKAHASHI, Iwao HAYAKAWA
2003 Volume 22 Issue 3 Pages
251-261
Published: 2003
Released on J-STAGE: February 12, 2009
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The cyclic loadings during mastication supposedly accelerate degradation of soft lining materials. The purpose of this study was to investigate the effects of cyclic loading on viscoelastic properties of soft lining materials. Two plasticized acrylics, two silicones and one isoprenebased monomer contained elastomer were selected. Cylindrical-shaped specimens, 10mm×10mmφ, were prepared. Twenty specimens were subjected to cyclic loading in a water bath at 37°C; another twenty specimens were without cyclic loading. The viscoelastic properties were measured using a creep-meter. The cyclic loading significantly decreased the heights of the two materials, the instantaneous elastic displacements of one acrylic liner and the viscous flows of three materials. The cyclic loading affected mainly delayed deformations. Therefore, cyclic loading was a useful method for evaluating the durability of soft lining material.
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Hiroyuki NAKAO, Suong-Hyu HYON, Sadami TSUTSUMI, Takuya MATSUMOTO, Jun ...
2003 Volume 22 Issue 3 Pages
262-271
Published: 2003
Released on J-STAGE: February 12, 2009
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In the regeneration and repair of missing tissues, synthetic polymer scaffolds need many pores to involve cells and to supply cells with nutrients. The control of the pore size of biodegradable L-lactide/ε-caprolactone copolymer foams was studied by changing the polymer concentration and the cooling temperature in the freeze-drying method. The mixtures of polymer and 1, 4-dioxane solution were poured into an 18-8 stainless steel Petri dish and frozen. The pore size of a polymer foam tends to increase from the bottom towards the top of a Petri dish. The pore size decreased to one-half with increasing polymer concentration (1 to 10wt%). The mean pore size in foams of 8% polymer concentration decreased from 100μm to 20μm as cooling temperature was lowered. This suggests that the higher cooling rate due to lower cooling temperature can produce smaller ice-crystals and result in smaller pores.
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Light Transmittance Characteristics
Hiroyuki ARIKAWA, Takahito KANIE, Koichi FUJII, Tetsuya HOMMA, Hideo T ...
2003 Volume 22 Issue 3 Pages
272-279
Published: 2003
Released on J-STAGE: February 12, 2009
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The purpose of this study was to examine the light transmittance characteristics of the paint-on resins for shade modification. Three shades of paint-on resin, one crown and bridge resin, and human enamel were used. Specimens with four different thicknesses (75-150μm) were prepared. The light transmittances including its wavelength distribution and diffusion characteristics were measured. The color values and the color differences among thicknesses of specimens were also determined. The light transmittance values of the paint-on resins ranged from 60.3% to 88.3% at 100μm thickness, which were lower or nearly equal in comparison with the crown and bridge resin and enamel. Although differences in the wavelength distribution of transmittance among materials were found at lower wavelengths, all materials showed similar diffusion characteristics. The thin layer of paint-on resin effectively changed the color of restorative resin. The paint-on resin may be an effective material for the modification of the color appearance matching required.
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Marie KOIKE, Jack L. FERRACANE, Hiroyuki FUJII, Toru OKABE
2003 Volume 22 Issue 3 Pages
280-291
Published: 2003
Released on J-STAGE: February 12, 2009
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A mercury plating technique was used to determine the phases forming on experimental Ag-Sn-Cu alloy powders (with and without Pd) exposed to electrolytically deposited mercury. Four series of alloy powders were made: a) 1.5% Pd with 10-14% Cu (CU series); b) 1.0% Pd with 10-14% Cu (1PD series); c) 1.5% Pd with different ratios of Ag
3Sn (γ) to Ag
4Sn (β) with 12% Cu (AGSN series); and d) 9-13% Cu with no Pd (NOPD series). Each powder was pressed on a freshly prepared amalgam specimen made from the same powder and metallographically polished until cross sections appeared; mercury was electroplated on the alloy particles. Alloy powders, amalgams and electroplated specimens were examined using XRD and SEM/EDS. XRD confirmed the presence of γ
2 in amalgams made from alloys with Cu<13% or with Ag
3Sn/Ag
4Sn>0.8. Specimens with moderately plated Hg showed γ
1 (Ag
2Hg
3) polyhedra and η' Cu
6Sn
5, but not γ
2. This method effectively identifies alloys prone to forming γ
2.
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Koichiro YAMAZAKI, Toru EGURO, Toru MAEDA, Hisayoshi TANAKA
2003 Volume 22 Issue 3 Pages
292-300
Published: 2003
Released on J-STAGE: February 12, 2009
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The purpose of this study was to examine the output energy changes of the contact probe for Er:YAG laser with tooth ablation and evaluate the effect of contact surface polishing on output energy. The Er:YAG laser was irradiated to enamel of extracted human incisors for 100min (5min×20times). The output energy of contact probes was measured every 5min (n=3). After 100min, the contact surfaces were polished using silicon carbide paper up to #1500, and the output energy of the probe was measured. The contact surfaces of the probes were observed and analyzed using an EPMA. After 100min, the output energy showed 49.4% of the energy of an unused probe. After the contact surfaces were polished to #1500, the output energy returned to 96.4% of baseline. It is suggested that the output energy of the contact probe decreased with tooth ablation, and polishing of the contact surface was effective to regain the energy.
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Satoru TANAKA, Tamisuke KISHI, Ryoji SHIMOGORYO, Shigeki MATSUYA, Kuni ...
2003 Volume 22 Issue 3 Pages
301-312
Published: 2003
Released on J-STAGE: February 12, 2009
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Biopex
® sets upon mixing with its liquid phase due to chelate reaction between sodium succinate and calcium phosphate, then gradually transforms to apatite. As a result of apatite formation, set Biopex
® shows excellent tissue responses and good osteoconductivity. However, Biopex
® would be washed out when the paste is exposed to body fluid before its setting reaction. Washed out cement causes an inflammatory response. In this investigation, therefore, sodium alginate was added to the liquid phase of Biopex
® and its effects on washout properties and transformation to apatite were studied. We found that cement remaining ratio, an index of the anti-washout property, of the Biopex
® increased by increasing the amounts of added sodium alginate to reach 100% when the liquid phase of Biopex
® contained 0.6% or more sodium alginate. Biopex
® gradually transformed to apatite regardless of the amount of added sodium alginate at least when the concentration of the sodium alginate in the liquid phase was 1.0% or less. It is concluded therefore, that addition of sodium alginate is very useful for Biopex
® to acquire the anti-washout property.
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Mitsuharu OKAMOTO, Atsushi MINE, Kazumi WATANABE, Daizo KAWAHARA, Hiro ...
2003 Volume 22 Issue 3 Pages
313-320
Published: 2003
Released on J-STAGE: February 12, 2009
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Plasma and halogen lamp units were used to photo-cure a composite resin for porcelain bonding. Mean shear bond strengths to dentin after light curing through porcelain of 1 and 2mm thickness ranged from 20 to 27MPa before and after thermocycling, indicating no significant effects due to porcelain thickness, curing method, or thermocycling, except for plasma curing for 3s through porcelain of 2mm thickness that overcame thermocycling. The mean bond strength in this group was significantly lower than both that before thermocycling and that of the porcelain of 1mm thickness. Knoop hardness values for plasma curing for 3s through porcelain of 2mm thickness were significantly lower than the others. These results suggest that plasma light for 3s is not sufficient to cure composite resin cement through porcelain of 2mm thickness.
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Part 2. Application of Developed Investment for Type 4 Gold Alloy
Akira NAKAI, Kiyoshi KAKUTA, Shin-ichi GOTO, Katuma KATO, Atushi YARA, ...
2003 Volume 22 Issue 3 Pages
321-327
Published: 2003
Released on J-STAGE: February 12, 2009
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The objective of this study was to evaluate the efficacy of the developed investment for the prevention of blackening of a cast Type 4 gold and to analyze the oxides on its surface in relation to the blackening of the alloy. The experimental investments were prepared using a gypsumbonded investment in which boron (B) or aluminum (Al) was added as a reducing agent. A Type 4 gold alloy was cast into the mold made of the prepared investment. The effect of the additives was evaluated from the color difference (ΔE
*) between the as-cast surface and the polished surface of the cast specimen. B and Al were effective to prevent the blackening of a Type 4 gold alloy and the color of the as-cast surface approached that of the polished surface with increasing B and Al content. The prevention of the blackening of the gold alloy can be achieved by restraining the formation of CuO.
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Masafumi KIKUCHI, Masatoshi TAKAHASHI, Osamu OKUNO
2003 Volume 22 Issue 3 Pages
328-342
Published: 2003
Released on J-STAGE: February 12, 2009
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Aiming at developing a dental titanium alloy with better mechanical properties and machinability than unalloyed titanium, a series of Ti-Nb alloys with Nb concentrations up to 30% was made. They were cast into magnesia-based molds using a dental casting machine and the mechanical properties and grindability of the castings were examined. The hardness of the alloys with Nb concentrations of 5% and above was significantly higher than that of titanium. The yield strength and tensile strength of the alloys with Nb concentrations of 10% and above were significantly higher than those of titanium, while the elongation was significantly lower. A small addition of niobium to titanium did not contribute to improving the grindability of titanium. The Ti-30%Nb alloy exhibited significantly better grindability at low grinding speed with higher hardness, strength, and Young's modulus than titanium, presumably due to precipitation of the ω phase in the β matrix.
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Yoshinori KADOMA
2003 Volume 22 Issue 3 Pages
343-358
Published: 2003
Released on J-STAGE: February 12, 2009
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Adhesion promoting monomers for dental metals, 5-(4-vinylbenzyl)-2-thiobarbituric acid (5VS), 6-(4-vinylbenzyl-
n-propyl)amino-1, 3, 5-triazine-2, 4-dithione (VBATDT) and 9, 10-epithiodecyl methacrylate (EP8MA), were synthesized and surface treatment agents were prepared by dissolving each monomer in ethanol or acetone. Four non-precious and three precious metal adherends treated with each agent were butt-jointed together with MMA-PMMA resins. After 2, 000 thermal cyclings in water, tensile bond strengths were measured and the percentage of area of cohesive failure after the tensile test was determined.
The bond strengths to precious metal alloys generally increased in the order of 5VS<VBATDT<EP8MA. Bonding durability against water based on overall failure mode analysis was improved in the following order: for precious metal alloys; 5VS<VBATDT≤EP8MA, and for non-precious metal alloys; EP8MA, VBATDT<<5VS.
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Katsuhisa IDE, Masayuki HATTORI, Masao YOSHINARI, Eiji KAWADA, Yutaka ...
2003 Volume 22 Issue 3 Pages
359-370
Published: 2003
Released on J-STAGE: February 12, 2009
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Proteins can interact with corrosion reactions in several ways. In this study, we investigated the effect of albumin on the corrosion resistance of titanium in the presence of fluoride. The effects of the NaF concentration, albumin concentration, and pH on the corrosion characteristics of commercially pure titanium (CP-Ti) were examined by means of electrochemical techniques.
The corrosion resistance of titanium decreased as the NaF concentration increased and as pH decreased. The corrosion resistance of titanium in NaF solutions was improved in the presence of albumin. The natural electrode potential was elevated, and the passive current density was reduced by albumin at a concentration of 0.01%. The polarization resistance rose with increased concentrations of albumin in fluoride solution. These results showed that the albumin in saliva and dental plaque affected the corrosion resistance of CP-Ti in fluoride solution.
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Effect of Size and Shape of the Fillers
Munehiro TSUNODA
2003 Volume 22 Issue 3 Pages
371-382
Published: 2003
Released on J-STAGE: February 12, 2009
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The effects of size and shape of calcium carbonate (CC) and hydroxyapatite (HA) fillers on the degradation of poly (DL-lactic acid-co-glycolic acid) (PLGA) were examined in the PLGA composite films containing 50 mass% of the fillers. The composite and unfilled films were prepared by our method reported previously. The films were immersed in phosphate-buffered saline (pH7.4) at 37°C for up to 12 weeks. The fate of the films was monitored by weighing and size exclusion chromatography. Blending HA and CC fillers to PLGA retarded the degradation of the PLGA matrix by obstructing the autocatalytic effect caused by carboxylic acid end groups. CC was a little more effective in retarding the degradation than HA. The size of the fillers showed a significant effect on the degradation. The effect of size was more marked in HA than in CC filler. The shape of CC filler had little effect on the degradation in the two shapes studied.
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Yasushi WAKAMATSU, Kiyoshi KAKUTA, Hideo OGURA
2003 Volume 22 Issue 3 Pages
383-396
Published: 2003
Released on J-STAGE: February 12, 2009
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A new wear testing system, which carries out toothbrush wear and simulated occlusal wear tests alternately, was developed. Differences in wear behavior among three modes of wears, combined wear, toothbrush wear and simulated occlusal wear, were investigated using polymethylmethacrylate (PMMA) and two commercial resin composites (Z100, APX). The area of the material loss after each test was measured on the worn surfaces to evaluate the different modes of wears. On PMMA and Z100, the toothbrush wear corresponded to the combined wear, suggesting that toothbrush wear was dominant in the combined wear for these materials. On the other hand, the occlusal wear was dominant corresponding to the combined wear on APX. Both the simulated occlusal wear and toothbrush wear tests are essential to evaluate the wear behavior of restorative materials, and the combined wear test is effective to analyze the wear behavior of restorative materials under different wear processes which consist of toothbrush wear and simulated occlusal wear.
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Tensile Bond Strength and Surface Modification
Yong Hoon KWON, Oh-Won KWON, Hyung-Il KIM, Kyo-Han KIM
2003 Volume 22 Issue 3 Pages
397-403
Published: 2003
Released on J-STAGE: February 12, 2009
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To test the feasibility of Nd:YAG laser ablation for orthodontic use, bovine enamels were ablated at 2.5 and 3.5W/pulse conditions. Orthodontic brackets were attached on the ablated enamel surface using a self-curing resin. For comparison, a 37% phosphoric acid solution was used to etch the enamel surface. The strength to detach the brackets was estimated for both surface treatments. Modifications of the enamel surfaces were also compared using a scanning electron microscope for both treatments. The tensile bond strengths from the laser-ablated enamels were significantly lower than that from the phosphoric acid-etched enamels. The higher laser power treatment gave a significantly higher bond strength average than with the lower laser power. The laser-ablated surfaces showed the formation of craters. The formation involved melting and solidification of enamel. Each crater had numerous micropores. Microscopically, the ablated surface was smooth, while much of the acid-etched surface contained numerous microspaces.
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Yong Hoon KWON, Oh-Won KWON, Hyung-Il KIM, Kyo-Han KIM
2003 Volume 22 Issue 3 Pages
404-411
Published: 2003
Released on J-STAGE: February 12, 2009
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The acid resistance of Nd:YAG laser-ablated enamel surfaces was studied by evaluating crystal structure, mineral distribution, and fluorescence radiance and image in the present study. For comparison, 37% phosphoric acid etching was performed. The formation of β-tricalcium phosphate (β-TCP) was confirmed in the laser-ablated surface. The Ca/P ratio increased after ablation due to mineral re-distribution. In contrast, the Ca/P ratio decreased after acid etching due to mineral loss. The laser-ablated enamels showed a smaller increase of fluorescence radiances and less clear laser confocal scanning microscope images than those observed in the acid-etched enamels. The former suggests a minimized mineral loss. The Nd:YAG laser irradiation will enhance the acid resistance and retard the carious progression in enamel.
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(I) Two Investments
Toshiko MORI, Janis MCALOON, Farzaneh AGHAJANI
2003 Volume 22 Issue 3 Pages
412-420
Published: 2003
Released on J-STAGE: February 12, 2009
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The present study compared the TE of two gypsum-bonded dental casting investments, the oldest K and more recent G. They had almost identical composition, 70% refractory (cristobalite) and 30% binder, but had different recommended water/powder ratios, 0.40 (K) and 0.33 (G). The average TE was significantly less (1.19%) in K than in G (1.45%); the volume decrease accompanied by the phase change of gypsum was more pronounced in the less dense K. When the dehydration conditions around gypsum are similar to those prevailing in wet calcinations methods, an expansion is likely to occur in the mold due to the formation of dental stone by recrystallization. This additional expansion has not been detected in ordinary laboratory measurement but can effectively increase the actual TE of an investment. The present study has proved the formation of dental stone by rapid heating of an investment. Specific laboratory techniques may have been supplementing low TE by this mechanism.
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