-
Chihiro TANI, Kazuo ITOH, Hisashi HISAMITSU, Sadao WAKUMOTO
1994 Volume 13 Issue 2 Pages
131-137,269
Published: December 25, 1994
Released on J-STAGE: February 12, 2009
JOURNAL
FREE ACCESS
The effect of adding micro filler to 4-META MMA/TBB dentin bonding agent was examined by measuring the wall-to-wall polymerization contraction gap of a commercial light-cured resin composite in a cylindrical dentin cavity and the tensile bond strength of the flat dentin surface. Gap formation was not completely prevented by using a filled dentin bonding agent although the tensile bond strength was significantly greater than that obtained using the unfilled dentin bonding agent. These results indicate that the addition of micro filler to the dentin bonding agent does not produce complete adaptation of the resin composite to the dentin cavity wall.
View full abstract
-
Masayuki KON, Fumiaki KAWANO, Kenzo ASAOKA, Naoyuki MATSUMOTO
1994 Volume 13 Issue 2 Pages
138-147,269
Published: December 25, 1994
Released on J-STAGE: February 12, 2009
JOURNAL
FREE ACCESS
Porcelains with leucite crystals dispersed into various glass matrices were prepared for investigating the effects of the leucite crystals on the mechanical strength of glassy porcelain. The strength of glassy porcelains containing leucite crystals was affected by the differences of thermal expansion coefficients, compositions and deformation temperatures of the glass matrices. In the case of a large mismatch of thermal expansion between the leucite crystals and boro-silicate glass, the strength decreased with increasing amount of leucite. In leucite porcelains using a feldspar glass matrix, there was little or no effect of leucite on the strength. However, the strength of porcelains consisting of leucite crystals and a soda-lime glass matrix was enhanced with increasing leucite content, compared with that of the glassy matrix alone. Such an increase in strength is considered to be because the interface between the glassy matrix and leucite particles occurred in continuous phases, with an effect due to fusion occurring during the transition from leucite particles to the glass phase.
View full abstract
-
Effect of Temporary Cement on Tensile Bond Strength of Resin Luting Cement
Rintaro TERATA, Kaoru NAKASHIMA, Masahiko OBARA, Minoru KUBOTA
1994 Volume 13 Issue 2 Pages
148-154,270
Published: December 25, 1994
Released on J-STAGE: February 12, 2009
JOURNAL
FREE ACCESS
This study was performed to investigate the effect of temporary sealing with cement on the tensile bond strength of resin luting cement to tooth substrate. Five temporary cements and five resin luting cements were used. Six hundred bovine incisor teeth were randomly divided between each group. Effect of temporary sealing on the tensile bond strength of resin luting cement varied in accordance with the temporary cement used. Temporary sealing with both the eugenol-containing and the eugenol-free temporary cements decreased the tensile bond strength of resin luting cement. The tensile bond strength with one of the resin luting cements was most stable on both enamel and dentin pretreated with all temporary cements tested.
View full abstract
-
Yohsuke TAIRA, Yohji IMAI
1994 Volume 13 Issue 2 Pages
155-163,270
Published: December 25, 1994
Released on J-STAGE: February 12, 2009
JOURNAL
FREE ACCESS
The effect of primers containing copper salts on adhesion between enamel and stainless steel was studied in a trial to improve durability of TBB type resin cements. Bovine enamel surfaces were treated with 10% phosphoric acid, then with acetone primers containing copper salts, and finally bonded with TBB resins. Tensile strengths of the bonded specimens were measured after thermocycling testing in water and compared with those obtained for commercial composite type resin cements. A combination of a primer containing copper (II) methacryloyloxyethyl succinate and 4-META/MMA-TBB resin was most effective in improving the durability, and superior to the commercial resin cements. The mean and lowest bond strength values of 21MPa and about 12MPa, respectively, were retained after 2, 000 thermocycles.
View full abstract
-
Takao HANAWA, Masayuki KON, Shoji OHKAWA, Kenzo ASAOKA
1994 Volume 13 Issue 2 Pages
164-173,270
Published: December 25, 1994
Released on J-STAGE: February 12, 2009
JOURNAL
FREE ACCESS
The diffusion of elements of commercial porcelain for titanium into titanium oxide during heating was investigated. Titanium was deposited on three kinds of disk-shaped porcelains by vacuum-vaporization and the porcelains were then heated. A thin titanium oxide film was formed on the porcelains by the heating. X-ray photoelectron spectroscopy was used to characterize the surfaces of the porcelains with and without titanium oxide. Only sodium, potassium, and barium diffused into titanium oxide during heating, where they formed a complex oxide with titanium. The diffusion of these elements may be involved in the bonding of porcelain to titanium.
View full abstract
-
Yoshiaki TANI, Toshihiro TOGAYA, Akiko ISHIKAWA, Yuko WATANABE, Keishi ...
1994 Volume 13 Issue 2 Pages
174-181,271
Published: December 25, 1994
Released on J-STAGE: February 12, 2009
JOURNAL
FREE ACCESS
We have previously reported that insertion of coarse particles of β-Quartz Glass Ceramic Insert (Megafiller) into a composite resin markedly reduced the polymerization shrinkage of resin restorative materials. In this study, we examined the effects of Megafiller insertion on wear resistance evaluated by the glass beads abrasion test, and the conventional toothbrushing abrasion test. The depth of wear was determined by measuring the thickness of the specimen before and after the wear tests using a profile projector accurate to 1μm. In general, the depth of wear of the composites was reduced by Megafiller insertion, but the differences in the depth of wear between composites with and without the Megafiller were not significant except for a few materials. There were slight differences in the wetness of Megafiller in some composite resins.
View full abstract
-
Kunio ISHIKAWA, Edward D. EANES, Kenzo ASAOKA
1994 Volume 13 Issue 2 Pages
182-189,271
Published: December 25, 1994
Released on J-STAGE: February 12, 2009
JOURNAL
FREE ACCESS
Effects of solution calcium ions on hydroxyapatite (HAP) formation from the hydrolysis of dicalcium phosphate anhydrous (DCPA) were investigated under controlled solution conditions. The hydrolysis experiments (2.5mmol DCPA/250mL) were carried out at fixed pH in the absence or presence of CaCl
2 (0-200mmol/L) by standard pH stat techniques at 37°C. The rate of hydrolysis was much faster, and the yield of HAP approximately doubled in the presence of CaCl
2 when compared to no CaCl
2, but no significant difference was observed over the range of Ca
2+ concentrations examined (25-200mmol/L). At equivalent conversion times, the crystallinity of the HAP formed was also greater in the presence of CaCl
2. Calculations showed that much less DCPA dissolved to reach solution equilibrium with respect to HAP in the presence than in the absence of CaCl
2. We conclude, therefore, that solution Ca
2+ is an important factor in controlling HAP formation from the hydrolysis of acidic calcium phosphates such as DCPA.
View full abstract
-
Yohji IMAI, Akiko SAITO
1994 Volume 13 Issue 2 Pages
190-197,271
Published: December 25, 1994
Released on J-STAGE: February 12, 2009
JOURNAL
FREE ACCESS
The effects of addition of various copper salts to 2-hydroxyethyl methacrylate (HEMA) primer were studied with regard to tensile bond strength of methyl methacrylate-tributylborane (MMA-TBB) resin to dentin. Bovine dentin surfaces were treated with 10% phosphoric acid, then with a primer consisting of aqueous 35% HEMA and a copper salt, and finally bonded to acrylic rods with MMA-TBB resin. The types of copper salts and concentrations in the primers were varied. The optimal concentration of copper salts in the primers was 0.5-3μmol/g. The primers containing copper salts of sulfate, methacrylate, methacryloyloxyethyl phthalate, or methacryloyloxyethyl succinate were especially effective among the eight copper salts studied in increasing bond strength, producing mean bond strengths of 14.2-16.1MPa and mean minimum values of 9.9-11.7MPa. These bond strengths were higher than those obtained with the commercial 4-META/MMA-TBB resin system. A model experimental study concerning the molecular weight of poly (MMA) formed in the presence of some copper salts suggested that the increase in bond strength was produced through an increase in molecular weight of MMA-TBB resin by the copper salts.
View full abstract
-
Rie NOMOTO, Keiko UCHIDA, Tadashi HIRASAWA
1994 Volume 13 Issue 2 Pages
198-205,272
Published: December 25, 1994
Released on J-STAGE: February 12, 2009
JOURNAL
FREE ACCESS
The depths of cure and the distributions of degree of conversion (DC), polymerization conversion (PC) and percent pendant double bonds (PDB) of light-cured composite resins cured under various intensities of light were investigated. When the total amount of exposure, represented by the product of the light intensity and the irradiation time, was kept constant, each of the depth of cure and the distributions of DC, PC and PDB were the same for each material regardless of the light intensity and irradiation time. The depth of cure could be expressed as a logarithmic function of the total amount of exposure. From regression analysis, the attenuation coefficient and the critical total amount of exposure capable of initiating polymerization of each composite resin could be determined.
View full abstract
-
Kiyoshi TAJIMA, Seijiro MATSUDA, Satoyuki KITAJIMA, Yuki YOKOYAMA, Hir ...
1994 Volume 13 Issue 2 Pages
206-213,272
Published: December 25, 1994
Released on J-STAGE: February 12, 2009
JOURNAL
FREE ACCESS
Oxygen density in the melting atmosphere, oxygen uptake, hardness and castability of pure titanium castings were examined to evaluate the efficacy of gas purging in reducing contamination from the melting atmosphere and mold, using a newly developed titanium casting machine in which the double purging process is systematized. The adoption of a double purging operation resulted in an extremely low oxygen density in the melting atmosphere, followed by extremely low oxygen uptake in the casting when compared with the conventional titanium casting machine. When the purging operation was used, the surface hardness was markedly reduced, although there was no difference in castability. From these results, it was suggested that the newly developed titanium casting machine with the double purging operation could produce better titanium castings with less contamination due to the mold and gas impurities in melting atmosphere.
View full abstract
-
Susumu HIRANO, Tadashi HIRASAWA
1994 Volume 13 Issue 2 Pages
214-219,273
Published: December 25, 1994
Released on J-STAGE: February 12, 2009
JOURNAL
FREE ACCESS
The compressive creep and the recovery of commecially available composites, 2 kinds for posterior and 2 kinds for anterior use, in water were examined. In posterior composites, creep strain after 500h at a stress level of 8.3kgf/mm
2 was significantly small (within 1%). The results of the compressive creep test showed that posterior composites would be resistant to occlusal stress. Creep strain was higher in anterior composites than that in posterior composites because of their lower inorganic filler content. The rate of recovery of composites was rapid immediately after the creep test. The water sorption of composites after 500h test was almost constant at some reduced stress levels, especially in posterior composites.
View full abstract
-
Suchit POOLTHONG, Toshiko MORI, Michael V. SWAIN
1994 Volume 13 Issue 2 Pages
220-227,273
Published: December 25, 1994
Released on J-STAGE: February 12, 2009
JOURNAL
FREE ACCESS
A comparison was made on the mechanical properties of three glass-ionomer cements, one of which was of experimental fiber-reinforcing and auto-curing type. Two others were proprietary auto-curing and light-activating cements. Biaxial flexure test was conducted on disc samples. Three-point bending test was also carried out on bar samples to determine modulus of elasticity and strength. All samples were kept at 37°C and 100% RH for 24h before testing under ambient conditions. A prolonged fracture process was observed in the experimental cement, demonstrating the effect of fiber incorporation in stabilizing the fracture process. The proprietary cements failed in a brittle manner. Comparison of the mechanical properties identified three characteristics. These were a high Weibull modulus resulting from the stabilization in fracture process, a modulus of elasticity value comparable to that of dentin, and a high biaxial flexure strength close to that of a dental resin composite.
View full abstract
-
Kazuhiko ENDO, Rohit SACHDEVA, Yoshima ARAKI, Hiroki OHNO
1994 Volume 13 Issue 2 Pages
228-239,273
Published: December 25, 1994
Released on J-STAGE: February 12, 2009
JOURNAL
FREE ACCESS
The structure of a titanium nitride film coated by arc ion plating on a Ni-50Ti shape memory alloy was characterized by X-ray photoelectron spectroscopy (XPS). The corrosion behavior of the titanium nitride-coated Ni-50Ti alloy was examined in 0.9% NaCl solution by potentiodynamic polarization measurements and a polarization resistance method. XPS spectra showed that the titanium nitride film consisted of three layers, a top layer of TiO
2, a middle layer of TiN
x (x>1), and an inner layer of TiN. The passive current density for the titanium nitride-coated alloy was approximately two orders of magnitude lower than that of the polished alloy in the potential range from the free corrosion potential to +500mV (vs. Ag/AgCl). Pitting corrosion associated with breakdown of the coated film occurred above this potential. The polarization resistance data also indicated that the corrosion rate of the titanium nitride-coated alloy at the free corrosion potential (+50-+100mV) was more than one order of magnitude lower than that for the polished alloy.
View full abstract
-
Part 1. Surface Aspects and Fit of Crowns
Shigeki MURAKAMI, Yoshio KOZONO, Takeshi ASAO, Yuki YOKOYAMA, Masahiro ...
1994 Volume 13 Issue 2 Pages
240-250,274
Published: December 25, 1994
Released on J-STAGE: February 12, 2009
JOURNAL
FREE ACCESS
Rapid burnout type gypsum-bonded investment materials were developed to shorten the time required for dental casting procedures. With these materials, molds can be prepared by rapid heating at 700°C for 30min from 30min after the start of mixing. When the investment block was rapidly heated at 700°C, no fractures were observed in the rapid burnout type investments with one exception, while a conventional cristobalite investment broke into pieces shortly after being placed in the furnace. Casting fins were sometimes induced only for the material which showed fracturing on rapid heating. No practical problems were found in the surface roughness of the castings. The 30min-setting expansion was significantly different among the materials although there were no differences in thermal expansion, and the material showing greater 30min-setting expansion was efficient to obtain better fit of the crown as in the conventional casting procedures.
View full abstract
-
Seiichiro FUJISAWA
1994 Volume 13 Issue 2 Pages
251-255,274
Published: December 25, 1994
Released on J-STAGE: February 12, 2009
JOURNAL
FREE ACCESS
2, 2-Bis [4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl] propane (bis-GMA) is widely used in dentistry as a monomer of composite resin system and their bonding agents. Since bis-GMA is not purified, its isomers and some chemicals such as residual initiator remain in the commercial product. Bis-GMA and iso-bis-GMA were separated from bis-GMA monomer by HPLC. NMR spectra of both monomers were recorded, and their all signals in 1H and 13C-NMR spectra were assigned using DEPT and COSY experiments.
View full abstract
