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Volume 20 (2001)
- Issue 4 Pages 247-
- Issue 3 Pages 195-
- Issue 2 Pages 127-
- Issue 1 Pages 1-
Volume 20, Issue 4
Displaying 1-11 of 11 articles from this issue
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Seiji BAN, Jiro HASEGAWA2001 Volume 20 Issue 4 Pages 247-256
Published: 2001
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSSupercritical water was used as a modification method of electrochemically deposited apatite on pure titanium. The apatites were coated on a commercially pure titanium plate using a hydrothermal-electrochemical method. A constant direct current at 12.5mA/cm2 was loaded for 1hr at 25, 60, 100, 150 and 200°C in an electrolyte containing calcium and phosphate ions. The deposited apatite on the titanium substrate was stored in supercritical water at 450°C under 45MPa for 8hr. With this treatment, the crystallinity of the apatites increased, sharp edges of the deposited apatites were rounded off, and the bonding strength of the titanium substrate to the deposited apatites significantly increased. On the other hand, weight loss in 0.01N HCl decreased and the weight gain rate in a simulated body fluid also decreased with this treatment. It is suggested that the modification using supercritical water improved the mechanical strength of the deposited apatite, but worsened its bioactivity.View full abstractDownload PDF (1959K) -
Shingo MATSUO, Fumio WATARI, Noboru OHATA2001 Volume 20 Issue 4 Pages 257-274
Published: 2001
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSLaser lithography was applied for Computer Aided Design and Computer Aided Manufacturing (CAD/CAM) fabrication of dental prostheses made of composite resin. First, the conditions to obtain the optimum resolution for photo-curing were determined, and then a composite resin full crown was fabricated by laser lithography. Second, a functionally graded composite resin post and core which had gradient elasticity in the post, was manufactured by the gradual change in the filler contents of the composite resin. Finally, stress analysis of the functionally graded post and core was performed by a two-dimensional finite element method. This demonstrated the effects of reducing the stress concentration around the apex of the post.View full abstractDownload PDF (4497K) -
Xing Yan WANG, Koji MIYAZAKI, Yoshio ITOH, Wataru MOTOKAWA2001 Volume 20 Issue 4 Pages 275-285
Published: 2001
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThis study aimed to investigate the fluoride-releasing ability of an experimental tooth separator consisting of polyurethane elastomer with tin fluoride and its effect on the acid resistance of human enamel. The tooth separator was set around an enamel slab and stored in de-ionized water for 10 days. The daily concentration of fluoride in the de-ionized water was measured. Then the enamel surface was artificially decalcified by a lactic acid buffer solution (pH 4.5) for 96 hours. The mineral density at the surface layer of the enamel was measured to evaluate the acid resistance. The fluoride release increased with the amount of fluoride in the separator, but decreased with the immersion time. Both the enamel area contacting with the separator and its surrounding area showed lower mineral loss and lesion depth compared with the controls (P<0.05). It is suggested that the experimental tooth separator would release enough fluoride and improve the acid resistance of the enamel surface layer.View full abstractDownload PDF (1962K) -
Effects of Sn, Ga, and In Additives on Properties of Ag-Pd-Au-Cu Alloy for Ultra-low Fusing CeramicsTomoyuki SHIMIZU, Shin-ichi GOTO, Hideo OGURA2001 Volume 20 Issue 4 Pages 286-304
Published: 2001
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSNine 35% Ag-30% Pd-20% Au-15% Cu alloys containing 2, 4 and 6mass% of Sn, Ga or In as an additive metal were experimentally prepared to investigate the effects of different additives and their content on the physical and mechanical properties as well as the bond with a ultra-low fusing ceramic. Both the different additives and their content or either of these two factors significantly influenced most of the evaluated properties except for the area fraction of the retained ceramic. Based on the evaluated properties three experimental alloys (2% Sn-added alloy, 4% Ga-added alloy and 2% In-added alloy) can be recommended as a suitable alloy for ceramicmetal restorations using ultra-low fusing ceramics.View full abstractDownload PDF (5419K) -
Masaharu NAKAGAWA, Shigeki MATSUYA, Koich UDOH2001 Volume 20 Issue 4 Pages 305-314
Published: 2001
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThe effects of fluoride concentrations and pH on the corrosion behavior of pure titanium, Ti-6Al-4V, Ti-6Al-7Nb alloys and a new Ti alloy adding palladium, which is expected to promote a repassivation of Ti were examined by anodic polarization and corrosion potential measurements. The amount of dissolved Ti was analyzed by inductively coupled plasma mass spectroscopy. The surface of the specimen was analyzed by X-ray photoelectron spectroscopy before and after the measurement. Pure Ti, Ti-6Al-4V and Ti-6Al-7Nb alloys were easily corroded even in a low fluoride concentration in an acidic environment. The corrosion resistance of Ti-0.2Pd alloy was greater than those of pure Ti, Ti-6Al-4V and Ti-6Al-7Nb alloys in the wide range of pH and fluoride concentrations. The high corrosion resistance of Ti-0.2Pd alloy was caused by the surface enrichment of Pd promoting a repassivation of Ti. The Ti-0.2Pd alloy is expected to be useful as a new Ti alloy with high corrosion resistance in dental use.View full abstractDownload PDF (859K) -
Ker-Kong CHEN, Yasuo SHONO, Takao OGAWA, Yoshio KOZONO, Masamichi TERA ...2001 Volume 20 Issue 4 Pages 315-324
Published: 2001
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSComparative studies on resin-dentin bond strength and failure mode were performed between the conventional tensile test and the microtensile test with non-trimming small specimens, 1×1mm in cross-section, for two brands of dentin bonding systems. The fracture surface of the conventional large specimen showed a catastrophic cohesive failure in dentin at its center and a lesser adhesive failure, suggesting that the whole failure was due to the development of some major cracks. The non-trimming microtensile test showed significantly larger average bond strength with markedly larger standard deviation and significantly larger fraction of adhesive failure than the conventional test. Some small specimens were extremely strong and some were weak according to the heterogeneous distribution of tight bonding and defective or deficient bonding over the whole dentin surface. These results suggest that the non-trimming microtensile test may potentially provide more realistic aspects of resin-dentin bonding than the conventional bulk specimen.View full abstractDownload PDF (2511K) -
Sejuty HAQUE, Shuichi TAKINAMI, Fumio WATARI, Mahfujul Haq KHAN, Motoy ...2001 Volume 20 Issue 4 Pages 325-338
Published: 2001
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThe radiation effects on the mechanical and physical properties of photo-polymerized UDMA resin without filler was investigated by various mechanical tests and spectroscopic measurements. The radiation sources were carbon ion (12C ion) and gamma ray (γ-ray). With 640Gy of 12C ion radiation, Vickers hardness increased by about 40%, the degree of abrasion decreased by 30%, and the flexural strength increased by 20%. With the same dose of γ-ray radiation, only Vickers hardness increased by 19%. The spectra taken by the Fourier Transform Infrared Spectrometer (FT-IR), Raman spectroscopy, and Fluorescence spectrophotometer showed little change in the peak configuration and background intensities. The relative degree of conversion (DC) of carbon double bonds by radiation to the state of non-radiated samples were estimated by FT-IR. Spectroscopic results were indicative for the formation of cross-linking between carbon chains. Cross-linking of carbon molecules induced by radiation might be one of the reasons for the improved mechanical properties of UDMA resin.View full abstractDownload PDF (2339K) -
Zutai ZHANG, Yukimichi TAMAKI, Takashi MIYAZAKI2001 Volume 20 Issue 4 Pages 339-344
Published: 2001
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSIn previous study, we found that Mg(H2PO4)2 instead of NH4H2PO4 was available as a binder material for phosphate-bonded investments and possibly could be used to develop the phosphate-bonded investment without ammonia gas release. The purpose of the present study was to develop the experimental ammonia-free phosphate-bonded investments by investigating suitable refractories. Mg(H2PO4)2⋅nH2O and MgO were prepared as a binder. Cristobalite and quartz were selected as refractories. The powder ratio of MgO/Mg(H2PO4)2⋅nH2O was set constant at 1.2 according to our previous findings. Fundamental properties of dental investment such as strength, manipulation and expansion were evaluated. Using cristobalite as the refractory material, further investigations were performed. The refractory/binder ratio was definitely effective. The increase of this ratio led to low mold strength and large mold expansion. The present findings suggested that C5 was desirable for dental investment.View full abstractDownload PDF (573K) -
Yohji IMAI, Atsushi OHYAMA2001 Volume 20 Issue 4 Pages 345-352
Published: 2001
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSAcrylic bone cements have been used in orthopedic surgery without detailed information on their basic characteristics, especially on their powder components. In this study, the powder components of seven bone cements available on the market in Japan were characterized for morphology, polymer structure and molecular weight, content of residual monomer and benzoyl peroxide (BPO), and thermal properties using scanning electron microscopy, nuclear magnetic resonance spectroscopy, size exclusion chromatography, high performance liquid chromatography, and differential scanning calorimetry, respectively. Considerable differences between the seven bone cements were found in polymer structure and molecular weight, and especially in BPO content and in the morphology of the polymer particles such as shape, size and distribution. It was found that the BPO content was not always in agreement with the value given by the manufacturers on the package.View full abstractDownload PDF (1848K) -
Mariko WATANABE, Toramine HASE, Yohji IMAI2001 Volume 20 Issue 4 Pages 353-358
Published: 2001
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThe change in the bisphenol A (BPA) content in a polycarbonate (PC) orthodontic bracket and its leaching characteristics were studied by immersing the bracket in water because BPA has been the matter of controversy in dentistry due to its estrogenic potential. PC brackets were placed in water at 37°C and 60°C and the BPA content in the bracket and the amount of BPA released into the water were analyzed at appropriate intervals by high performance liquid chromatography. The BPA content increased in the water with time and was 3.8-fold after 12 months at 37°C and 12.4-fold after 14 weeks at 60°C compared with the virgin value. The rate of BPA release also increased with time. The results suggested that BPA was released from the bracket time-dependently in the oral cavity. However, it was assessed that little or no estrogenic effect due to the released BPA is expected in the human body.View full abstractDownload PDF (624K) -
Chihiro TANI, Kazuo ITOH, Hisashi HISAMITSU, Sadao WAKUMOTO2001 Volume 20 Issue 4 Pages 359-368
Published: 2001
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThe bonding efficacy of sclerotic dentin was determined by measuring the polymerization contraction gap width of a commercial light-activated resin composite in a cervical defect and by measuring the micro-Vicker's hardness at the dentin adhesive surface; morphological characteristics were observed using a scanning electron microscope in extracted human incisors and premolars. Contraction gap formation was completely prevented when the cavity wall was primed with 35vol% glyceryl mono-methacrylate solution after 0.5mol/L EDTA conditioning. The contraction gap width was significantly decreased when the resin composite was filled into the sclerotic dentin cavity even when priming was omitted. These results suggest that the sclerotic dentin, which is frequently observed in cervical defects, should be preserved as a substrate because it exhibits an effect of dentin priming and is suitable for bonding.View full abstractDownload PDF (4804K)
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