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Volume 19 (2000)
- Issue 4 Pages 329-
- Issue 3 Pages 211-
- Issue 2 Pages 99-
- Issue 1 Pages 1-
Volume 19, Issue 4
Displaying 1-11 of 11 articles from this issue
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The Effects on the Water Absorption, Adhesive Strength and Mechanical Properties of Acrylic Denture Base ResinsTakahito KANIE, Koichi FUJII, Hiroyuki ARIKAWA, Katsuichiro INOUE2000 Volume 19 Issue 4 Pages 329-337
Published: 2000
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThe adhesive strength of porcelain artificial teeth and polymethylmethacrylates (PMMAs), which contained silanes with various number of vinyl or ethoxy groups, and the mechanical and physical properties of the PMMAs were measured. Four types of PMMAs with silanes showed high adhesive shear strength and caused fractures in the porcelain. Water absorption of the PMMAs increased with the addition of silane, but that of one type with silane was almost the same as the PMMA only type. The flexural strengths of the PMMAs with silane, except for one type, showed no significant differences compared with that of PMMA (p<0.05). The Tg levels of all PMMAs with silane fell less than that of PMMA. From these results, it was found that PMMA with silane from three vinyl groups and one ethoxy group showed excellent chemical bonding to porcelain and low water absorption.View full abstractDownload PDF (1188K) -
A Method for Evaluating Color Stability of Light-cured Composite Resins Using an Experimental FilterHiroyuki ARIKAWA, Takahito KANIE, Koichi FUJII, Naoyuki SHINOHARA, Hid ...2000 Volume 19 Issue 4 Pages 338-345
Published: 2000
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThe purpose of this study was to investigate a method for evaluating color stability of lightcured composite resins using an experimental filter that simulates human enamel. The light transmission coefficients and their spectral distributions from 400 to 600nm of twelve enamel specimens were measured. The experimental filter was designed so that its light transmittance characteristics were similar to those of enamel. Color stability tests for ten shades of two light-cured composite resins, which were irradiated directly and indirectly through the experimental filter with a light source, were performed. Despite different irradiation procedures, most materials exhibited significant color changes in the color stability test. Although the differences were small, the group of specimens irradiated indirectly through the filter showed significantly higher color differences in comparison with those irradiated directly. Our results indicate that the light attenuating effect of enamel affects the color stability of light-cured composite resins.View full abstractDownload PDF (1336K) -
Atsushi OHYAMA, Yohji IMAI2000 Volume 19 Issue 4 Pages 346-351
Published: 2000
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThe thermal behavior of eight dental acrylic resin powders was studied using differential scanning calorimetry (DSC). In addition, high performance liquid chromatography was performed to supplement the DSC analysis. The HPLC analysis revealed that the contents of residual monomers and benzoyl peroxide (BPO) in the powders were 0.01-0.97mass% and 0.25-1.28mass%, respectively. All the resin powders produced one broad exothermic peak, while a mixture of BPO and PMMA powders generated two peaks. One peak pattern was assigned to the decomposition of BPO included within the polymer particles. The results suggested that BPO was present inside the particles and little BPO was mixed into the resin powders. Moreover, the present study demonstrated a unique useability of DSC in characterizing resin powders.View full abstractDownload PDF (491K) -
Seiji BAN, Taizo WATANABE, Noriyasu MIZUTANI, Hisao FUKUI, Jiro HASEGA ...2000 Volume 19 Issue 4 Pages 352-362
Published: 2000
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSExternal oxides of a commercially pure titanium (cpTi), Ti6A14V alloy, and an experimental β-type titanium alloy (Ti 53.4wt%, Nb 29wt%, Ta 13wt%, and Zr 4.6wt%) were characterized after heating to 600, 900, 1150, and 1400°C in contact with three types of investments (alumina cement, magnesia cement, and phosphate-bonded) in air. XRD studies demonstrated that MgO, Li2TiO3 and/or Li2Ti3O7 were formed through reactions with the metal and the constituents in the magnesia cement-investment after heating to 900, 1150, and 1400°C. Except for these conditions, TiO2 (rutile) was only formed on cpTi. For titanium alloys, the other components apart from Ti also formed simple and complex oxides such as Al2O3 and Al2TiO5 on Ti6Al4V, and Zr0.25Ti0.75Nb2O7 on the β-type titanium alloy. However, no oxides containing V or Ta were formed. These results suggest that the constituents of titanium alloys reacted with the investment oxides and atmospheric oxygen to form external oxides due to the free energy of oxide formation and the concentration of each element on the metal surface.View full abstractDownload PDF (2084K) -
Tomomasa TAKATSUKA, Norifumi KONISHI, Satoshi NAKABO, Takeshi HASHIMOT ...2000 Volume 19 Issue 4 Pages 363-372
Published: 2000
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSWe investigated the initial adhesion in vitro of oral streptococci to porcelain inlays. Four strains of streptococci, Streptococcus mitis NCTC12261, Streptococcus oralis ATCC9811, Streptococcus sanguis ATCC10556 and Streptococcus sobrinus OMZ176, were used in this study. The disc specimens were made of porcelain, composite resin cement and human enamel. These specimens, with or without a saliva-coat, were immersed in a suspension of each streptococci strain at 37°C for 1hr, and the numbers of cells adhering to specimens were counted after staining. The saliva-coat significantly decreased the numbers of adhering cells in all strains tested (t-test, p<0.05). The adhesion to the porcelain and resin cements could be explained by a thermodynamic approach, although the adhesion to enamel could not be explained. These results indicated the possibility that the mechanism is different in initial adhered strains of streptococci between enamel and dental restorative materials.View full abstractDownload PDF (935K) -
Shoji TAKEDA, Mari AKIYAMA, Kiyofumi SAKANE, Tatuji SAKAI, Masaaki NAK ...2000 Volume 19 Issue 4 Pages 373-380
Published: 2000
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThe effects of metal combinations on cytotoxicity were examined following dynamic extraction by freely gyrating two spherical metals in a glass vessel. The cell viabilities of an Au alloy, a Ag-Pd-Au alloy and Ti were little affected by combinations among three metals. Cell viability ranged between 60 and 80% when precious alloys were in combination with Co-Cr or Ni-Cr alloys. Ti showed a clear difference in cell viability either in combination with Co-Cr or Ni-Cr alloys. The cell viability of the Ti/Co-Cr alloy combination was the same as that of precious alloys/Co-Cr or Ni-Cr alloy combinations. However, in an analogy with Co-Cr alloy Ni-Cr alloy combination, the Ti/Ni-Cr alloy combination depressed the cell viability below 20%. This suggested that when new metals are to be used in combination with dissimilar metals, the cytotoxicity of the metals could be evaluated in extraction conditions using the mutual dynamic contact of dissimilar metals.View full abstractDownload PDF (788K) -
Teruo KASAI, Kunio ISHIKAWA, Kazuomi SUZUKI, Hirofumi YATANI2000 Volume 19 Issue 4 Pages 381-388
Published: 2000
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSAlumina form and a porous apatite, apaceram®, were implanted in rat tibiae bone defects for up to 12 weeks and the tissue response was studied histologically as an initial evaluation of whether or not this ceramic form had potential as a reconstructive material for bone defects. We observed no bone formation inside the pores of porous apatite, even after 12 weeks, if the pores were deeper than 1.0mm from the surface. In contrast, we observed bone tissue deep inside the alumina form as early as 2 weeks after implantation. However, the bone that formed around the alumina form did not directly contact with the frame of the alumina form, even though bone directly contacted with porous apatite. We concluded, therefore, that the ceramic form has potential value as a reconstructive material for bone defects. This potential value would be further increased if the ceramic form could be prepared with calcium phosphate-related materials.View full abstractDownload PDF (2870K) -
Kazuomi SUZUKI, Kunio ISHIKAWA, Katsumi SUGIYAMA, Hiroaki FURUTA, Fumi ...2000 Volume 19 Issue 4 Pages 389-395
Published: 2000
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSBisphenol A (BPA) is an endocrine disruptor, and is used as a raw material for bisphenol A diglycidyl methacrylate and polycarbonate, that are used in the dental materials. In this study, the total and released amounts of BPA from polycarbonate-based dental materials were measured with high-pressure liquid chromatography (HPLC). The specimens used were orthodontic brackets and denture base resins in the same condition as when obtained commercially were cut into 3×3×4mm pieces and crushed into powder. The HPLC analysis was carried out after immersion of the specimens in water or ethanol for a determined time. The total amount of BPA in the specimens was analyzed after dissolution in chloroform. The amount of BPA released after immersion in water for 1hr was 0.01-0.4μg/g for the block samples and 0.14-4.22μg/g for the crushed samples, while that in ethanol for 1hr was 0.12-9.42μg/g for the block samples and 0.42-22.24μg/g for the crushed samples. The control of BPA in the denture preform resin was 78.9μg/g and this increased to 90.2μg/g after heating to form dentures and then to 250μg/g with mechanical crushing. The results of this study indicate that BPA is released from polycarbonates used in dentistry, and that the thermal conditions during the manufacturing of restorations may cause polymer decomposition resulting in the formation of BPA.View full abstractDownload PDF (1487K) -
Setsuo SAITOH, Yoshima ARAKI, Ryuichi KON, Hirohumi KATSURA, Masayuki ...2000 Volume 19 Issue 4 Pages 396-404
Published: 2000
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSTo elucidate the mechanism of dimensional changes in alginate impression in solutions, the relationship between the ion concentrations in three types of solutions (nonelectrolyte and monovalent and divalent metallic salts) and change in gel volume was examined. The gel in the monovalent metallic salt solution expanded and a decrease in monovalent cation and an increase in Ca2+ were observed. This suggests that the crosslinking density of the gel reduced due to dissociation of Ca2+ from the calcium alginate gel. In divalent metallic salt solutions, the shrinkage occurred according to crosslinking of unreacted residue. In the nonelectrolytic solution, gel, neither ethylene glycol nor acetonitrile showed any volume changes, while that in glutaraldehyde contracted. It is speculated that the former two solutions were affected by the fact that the gel has no semipermeability, and that the latter result was due to chemical interaction between the gel and solution.View full abstractDownload PDF (861K) -
Michio SHIMAKURA, Masaharu YAMAMOTO, Ken NAKAJIMA, Nobuya YOSHIDA2000 Volume 19 Issue 4 Pages 405-412
Published: 2000
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSTitanium is a difficult metal to grind, and thus mechanical polishing using conventional rotating tools takes a lot of time. The purpose of this study was to examine the polishing effect of a centrifugal shooting type polishing system on a pure titanium surface processed with a CAD/CAM system. The specimens' surfaces were polished for various times using this apparatus, then the center line average roughness (Ra) of each specimen was measured with surface roughness measuring apparatus. In addition, the surfaces after polishing were observed with a scanning electron microscope. After 50sec of polishing, Ra decreased from 1.1μm to less than 0.6μm, and after 60sec of polishing the cutting marks generated by the CAD/CAM system disappeared and a smooth surface was observed. Therefore, it appears that a centrifugal shooting type polishing system is effective at polishing pure titanium.View full abstractDownload PDF (2549K) -
Qazi MD HARUN-URASHID, Yukimichi TAMAKI, Zutai ZHANG, Atsushi OZAWA, T ...2000 Volume 19 Issue 4 Pages 413-421
Published: 2000
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThe purpose of this study was to investigate the application of a heat-shock method to fabricate titanium cast plates. Duplications of a maxillary model were prepared using DM under different firing schedules. Molds with patterns on the duplications were made by an outer investment (D), followed by heat shock at 850°C. Duplications heat shocked at 850°C after 30 min from mixing exploded within a few minutes. This explosion was successfully avoided by a drying procedure prior to the heat-shock. The molds were available for the heat shock at 850°C when the duplicate models were prepared by firing either using the conventional method and the heat shock above method described. Therefore, we could reduce the preparation time from about 16hr with the conventional method to about 10hr at the longest with the heat-shock method. These results suggested that the heat-shock method was labor-saving for fabricating titanium cast denture plates when controlling preliminary conditions prior to use.View full abstractDownload PDF (1872K)
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