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Volume 11 (1992)
- Issue 2 Pages 119-
- Issue 1 Pages 1-
Volume 11, Issue 2
Displaying 1-9 of 9 articles from this issue
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Asahi KITSUGI, Osamu OKUNO, Tsuyoshi NAKANO, Hitoshi HAMANAKA, Takayuk ...1992 Volume 11 Issue 2 Pages 119-129,217
Published: December 25, 1992
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSRare earth magnets have corrosive problems associated with their use in prostheses in various fields including orthodontics. The purpose of this study is to investigate the corrosion behavior of an Nd2Fe14B magnet and a SmCo5 magnet in an oral environment. The relations among the attractive force changes, the released elements, the weight changes and the anodic polarization measurements of the magnets were examined under immersions in 1% NaCl, 1% lactic acid, 0.05% HCl, 0.1% Na2S and Greenwood's artificial saliva at 37°C for forty-two days. The results showed that the rare earth magnets underwent high corrosive assaults and large attractive force reductions by the immersions in 1% lactic acid and 0.05% HCl. The problem of corrosion of the magnets could be overcome by sealing them within laser-welded stainless steel capsules.View full abstractDownload PDF (2973K) -
Seiji BAN, Toshikage JINDE, Jiro HASEGAWA1992 Volume 11 Issue 2 Pages 130-140,217
Published: December 25, 1992
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSOctacalcium phosphate (OCP) was implanted in both thigh muscle pouches of ddY-mice for 3 weeks, and was soaked in a simulated body fluid (SBF) and 1% NaCl solution maintained at 37°C for 1 day, 1 week and 3 weeks. After implantation or soaking, the specimens were characterized by scanning electron microscopic analyses, X-ray diffractometry, and infrared absorption spectroscopy. X-ray diffraction study showed that OCP had been completely transformed to apatite with low crystallinity such as the mouse's femur after a 3 -week implantation in the mouse body, and an apatic crystal was formed after soaking in the NaCl solution. The IR absorption spectra revealed that CO3 was incorporated in the apatite formed from OCP in both the mouse body and the NaCl solution, while OCP changed little after soaking in the SBF. It seems that the magnesium ion retards the transformation of OCP to apatite.View full abstractDownload PDF (2924K) -
Fumio NISHIMURA, Hideo NAKAMURA, Fumio WATARI, Itaru TANAKA, Hidekazu ...1992 Volume 11 Issue 2 Pages 141-149,217
Published: December 25, 1992
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSA new tensile fatigue test using a stainless steel screw was introduced. A transparent PMMA rod was selected as the test material. A hole was drilled and tapped into the rod; a screw was put into the rod with dental cement or without cementation. Three types of cyclic loads were applied to the test piece; the number of times the load was applied when the initial crack was observed and when the final fracture occurred were recorded. Surface observation showed that actual fatigue fractures occurred in the test piece. The preferred applied load waveform was the cyclic haver-triangles load because of the small coefficient of variance. Fatigue strengths of test pieces with and without cementation were different. Cementation improved the fatigue properties, and the type of cement had an effect on the fatigue properties. Although the number of final fractures minus the number of initial cracks was the constant regardless of the type of cement used.View full abstractDownload PDF (3828K) -
Ikuro HARASHIMA, Takashi UZAWA, Tadashi HIRASAWA1992 Volume 11 Issue 2 Pages 150-156,218
Published: December 25, 1992
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSA new testing system was developed for assessment of marginal sealability of dental restorations. It was constructed with a thermocycle loading line and a leakage detecting line partitioned from each other by the restoration under evaluation. The hot and cold solutions of rhodamine B as a tracer were alternately circulated in the thermocycle loading line by the switching of six solenoid valves. Marginal leakage of the tracer into distilled water circulating in the detecting line was periodically monitored by a spectrometer while thermocyling the restoration. The leakage data could be analyzed on the basis of an empirical formula. In application of this method, the durability of a complete seal against thermal changes was estimated on three teeth each of which was restored with an inlay, an amalgam or a glass ionomer.View full abstractDownload PDF (1054K) -
Takayuki YONEYAMA, Hisashi DOI, Hitoshi HAMANAKA1992 Volume 11 Issue 2 Pages 157-164,218
Published: December 25, 1992
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThe influence of composition and purity of titanium on the mechanical properties and the transformation temperatures of Ni-Ti alloy dental castings was investigated by tensile testing and differential scanning calorimetry (DSC). The compositions of the ingots were 49.0-49.2at% of titanium content. Three grades of titanium of relatively high purity were used as starting materials.
The result showed Ni-49.0Ti to be a somewhat brittle property, and Ni-49.2Ti to have low apparent proof strength and large elongation. Residual strain increased with increasing titanium content. Even small reductions of titanium purity influenced the tensile properties and the transformation temperatures, causing high apparent proof strength, low residual strain and low elongation because of the reduction in transformation temperatures.View full abstractDownload PDF (1176K) -
Susumu HIRANO, Tadashi HIRASAWA1992 Volume 11 Issue 2 Pages 165-176,218
Published: December 25, 1992
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThe compressive creep and the recovery of composites in water were examined. The creep strain of the composites after a 500h test linearly decreased with the increase of their filler content.
Their water sorption during testing decreased with the increase of applied stress on the composites containing low filler contents. In the composites containing high filler contents, the water sorption was almost constant for some stress levels.
The recovery of the composites after testing was significant immediately after testing. From the measurement of the water sorption of the composites, the microcrack or the craze should occur at the filler/matrix interface or in the matrix itself during the creep test, and water could diffuse to the microcrack or the craze after testing in unstressed conditions.
This would explain the increase in the water absorbed in the composites in the recovery period.View full abstractDownload PDF (2173K) -
Rie NOMOTO, Tadashi HIRASAWA1992 Volume 11 Issue 2 Pages 177-188,219
Published: December 25, 1992
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSMicroareas (100×100μm2) of thin visible light-cured composite sections irradiated for 10-60s were analyzed with a Fourier transform infrared spectrometer equipped with a microscopic unit before and after extraction of residual monomers to determine the percent unreacted double bonds (UDB) and percent pendant double bonds (PDB). The percent eluted double bonds (EDB) was calculated using these percents. Analysis was conducted at various depths along the midline from the irradiated surface to the base.
There were significant differences among the tested materials at each depth in UDB, PDB and EDB percents. The percent PDB of each material remained almost constant (25-40%) to a certain depth. This depth was equivalent to 70-80% of the depth of cure for each material. The range of depths at which percent PDB was constant indicated greater than 35-40% degree of conversion. At these locations, the composites may polymerize with a high rate of crosslinking.View full abstractDownload PDF (1422K) -
Yasumasa FUKASE, Masahiro SAITOH, Masahiro KAKETANI, Masayoshi OHASHI, ...1992 Volume 11 Issue 2 Pages 189-196,219
Published: December 25, 1992
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThermal coefficients of four kinds of commercially available paste-paste type pulp capping cements were examined. Control reference samples were made of dentin. A thermal coefficient analyzer was used, heating specimens for a few nanoseconds by a xenon flash bulb and measuring thermal changes by using a thermocouple. Thermal coefficients were examined by this non-steady state method. Thermal conductivities of all cements were almost the same or lower than that of dentin. Therefore, when each cement was heated, the penetrating energy was almost the same or lower than that of dentin. The thickness of the cements was converted into that of the dentin by using the obtained thermal conductivity. The 1-mm thicknesses of the examined cements were equal to between 0.97-mm and 2.10-mm thicknesses of lost dentin. The use of a pulp capping cement provided better pulp protection from thermal stimuli than did the same thickness of dentin.View full abstractDownload PDF (1199K) -
Toshiko MORI, Graham THOMAS, Robert MARKHAM, Paul WHITE1992 Volume 11 Issue 2 Pages 197-203,219
Published: December 25, 1992
Released on J-STAGE: February 12, 2009
JOURNAL FREE ACCESSThe heating performance of prototype variable power control units attached to two domestic microwave ovens, 500W and 700W, was investigated. The units employed the phase control method where rated voltage was obtained by switching AC supply at a particular angular position on the sinusoidal voltage. In order to create experimental conditions employed in a previous study, Sydney tap water (50mL) was heated at a 10% power level in the 500W oven. Water boiled at 10min in both experiments. However, the precision and control of the heating was greatly improved with addition of the control unit. A disinfecting solution (50mL) and a tissue fixative (10mL) were included for experiments with the 700W oven. A power level of only 1% was sufficient to maintain the temperature of the fixative at low temperatures (30-40°C) where many biological reactions occur. The present results indicate that microwave heating power can be controlled by the variable power control method. This will make temperature control possible through the provision of an electronic feedback loop which links a thermocouple with the power control unit.View full abstractDownload PDF (1465K)
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