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Biomedical subjects

N Kuwayama

Publications and source records attributed to N Kuwayama.

68 records · Page 4Linked to original sources
PubMed1980

[Studies on the mechanical properties of a metal-ceramic restoration. (Part I) Estimation of the bond strength by pull-out test (author's transl)].

Metal-ceramic composite materials as a porcelain fused to metal restoration, have been used for biomaterials. But the chief objection, to use of these materials as restorative materials, is its lack of strength, particularly tensile and shear strength. And the materials to have strong bond strength have been studied. On the other hand, the bond strength along metal-ceramic interface have usually measured by a pull out test. At the same time, the objection of the pull out test are pointed out. So, the deformation of metal-ceramic composite materials by the pull out test were simulated to use the axi-symmetric finite element method. And shear stress distribution along the interface and the principal stress distribution in ceramic were calculated. The following results were obtained. (1) Shear stress along the interface and maximum principal stresses in ceramic and in metal decrease rapidly along the interface. (2) The stress concentration factor as the case of the alloy with high Young's modulus is smaller than that of the alloy with low Young's modulus. So, the former would be stronger about the pull out test. (3) Metal-ceramic interface length is not affected for shear stress concentration. If the specimen has more than the critical interface length, the initial crack in ceramic would be occurred at the same pull out force.

Dental Bonding↗
PubMed1976

[Studies on alumina ceramics for dentistry--sinterable alumina for core material-- (author's transl)].

This study has been performed to introduce the industrial alumina ceramics having superior physico-chemical properties and desirable color for human tooth into dental field. The following results have been obtained through a series of experiments: 1) Effects of sintering of pure alumina powder were promoted more remarkably by adding a couple of additive together than by adding each, independently. 2) By adding a couple of additive, Li2O-Nb2O5 or MgO-Nb2O5, the effect of sintering was higly promoted, and tooth colored specimen was obtained. 3) At the alumina specimen sintered with 0.125 mol% of Nb2O5, a few initial shrinkage was seen and the process was followed by slowly increasing shrinkage through a rapid rate of heating. This suggested that a rapid heating was possible to be tried by using above additives. 4). The alumina ceramics with a couple of MgO-Nb2O5 prepared by heating at 1500 degrees C for 100 min., showed maximum bending strength of 42 kg/mm2 and 92.3 of R.A. hardness, which are rather higher value among other alumina ceramics. Though the luminosity might be too higher, chromaticity was as same as that of tooth shade.

Aluminum↗
PubMedDate not supplied

Correlation between microstructure of Ag-Pd-Au-Cu alloy and changes in shape on aging.

An investigation has been carried out to study changes in shape on aging in plastic deformed Ag-Pd-Au-Cu alloys. The changes in shape were measured in order to establish a relationship to the aging heat treatments. Their microstructure was observed in order to clarify this phenomenon at the same time. They were also investigated quantitatively using a feature analysis system. The changes in shape were interpreted as the shrinkage in volume resulting from the formation of the ordered phase. They were smaller at aging temperatures below 673 K. The change in microstructure was different at aging temperature between 573 and 773 K. These phenomena were due to the following: First, nodules which nucleated at the grain boundaries would have grown into the grains well before the formation of the ordered phase, and second, the shrinkage in volume would have been of a different kind that the ordered phase. Therefore aging treatments should be carried out at low temperature in order to minimize the changes in shape. Also, nodular growth should be inhibited in order to maximize the hardening in Ag-rich alloys.

Alloys↗
PubMedDate not supplied

Mechanical properties and biomechanical compatibility of porous titanium for dental implants.

Titanium powder with a granule diameter of 420-500 micron was prepared and porous titanium specimens were made from this powder. The mechanical properties of these specimens were examined. The compressive strength and low cyclic compressive fatigue strength were 182 and 40 MPa, respectively. Fractography was also observed by scanning electron microscopy. Typical fatigue characteristics of the bonding areas of the powder were observed. In addition, porous-titanium-coated dental implants with pure titanium cores were prepared. The compressive strength of the material used was 230 MPa, fatigue strength not being improved. Biomechanical stress calculations using the finite element method were made using a model that employed the use of the material implanted in alveolar bone. Shear stress at the implant-bone interface as well as compressive stress concentrations in the bone was calculated. The most suitable elastic modulus for the dental implant was then estimated from these calculations. Finally, based on these results, the use of porous titanium for dental implants was assessed.

Chemical Phenomena↗
PubMedDate not supplied

Histochemical detection of carbohydrates of Blastocystis hominis.

The carbohydrates of Blastocystis hominis were detected by histochemical techniques using light and electron microscopy. B. hominis, fixed with various fixatives, followed by treatment with detergents, were stained with periodic acid-Schiff (PAS) or alcian blue (AB). Intense PAS reactions were observed in cells fixed with glutaraldehyde or 1/2 Karnovsky fixative. The cells fixed with other fixatives showed weak or no reactions with PAS staining. Similar results were seen in the case of AB stain. These results indicated that, depending on the fixative used, B. hominis contained PAS- or AB-reactive carbohydrates. At the electron microscopic level, ultrathin sections of B. hominis were stained with periodic acid methenamine silver (PA-MS) or periodic acid thiocarbohydrazide-silver proteinate (PA-TCH-SP) staining techniques. Intense, positive reactions with PA-MS or PA-TCH-SP were observed on the central vacuole, Golgi apparatus, and cytoplasmic vesicles. The filamentous layer showed moderate reactions with PA-MS, whereas in PA-TCH-SP stain, it was stained more densely. The staining intensity of the central vacuole varied from cell to cell. The presence of membrane fusions of the cytoplasmic vesicles with the central vacuole indicated the accumulation of carbohydrates in the central vacuole.

Alcian Blue↗
PubMedDate not supplied

Intracranial dural arteriovenous fistulas with retrograde cortical venous drainage: assessment with cerebral blood volume by dynamic susceptibility contrast magnetic resonance imaging.

BACKGROUND AND PURPOSE: Retrograde cortical venous drainage (RCVD) is the most major risk factor for aggressive behavior of intracranial dural arteriovenous fistulas (DAVF). The purpose of this study was to assess the efficacy of relative cerebral blood volume (rCBV) map for RCVD in patients with DAVF. METHODS: Ten patients with angiographically proven DAVF with RCVD, 2 reference patients with DAVF without RCVD, and 10 control subjects underwent examinations with dynamic susceptibility contrast (DSC)-MR imaging. Four patients with DAVF with unilateral RCVD were evaluated, before and after treatment. The calculation of mean rCBV ratio was performed on a hemispheric basis. The mean rCBV ratio was defined as the value on one side (higher value side) divided by that on the other side (lower value side). RESULTS: In all patients with DAVF with RCVD, the rCBV map showed an increase in rCBV of the angiographically proved affected hemisphere. In 2 reference patients with DAVF without RCVD and all control subjects, the rCBV map showed no increase of rCBV. The mean rCBV ratio in patients with DAVF with RCVD was significantly higher than that of control subjects (P = .0002). Treatment response for RCVD was indicated by a decrease of CBV on the rCBV map and by a decrease of 22% in the mean rCBV ratio. CONCLUSIONS: Increased rCBV by DSC-MR correlated with RCVD in patients with DVAF. The assessment with rCBV for RCVD may be more quantitative than that with angiogram.

Aged↗
PubMedDate not supplied

Results of urgent thrombolysis in patients with major stroke and atherothrombotic occlusion of the cervical internal carotid artery.

PURPOSE: Atherothrombotic occlusion of the cervical internal carotid artery (ICA) without collateral flow is one of the most critical forms of acute ischemia. We report the results of urgent thrombolytic treatment of patients with major stroke in this clinical category. METHODS: Clinical findings and outcome in 33 patients were investigated. All patients had suffered a major stroke, with a score of 24 or higher on the NIH Stroke Scale on admission. Ischemic abnormalities were not detected on initial CT studies. Diagnoses were made at angiography, and patients were treated by intravenous or intraarterial local thrombolysis within 6 hours of stroke onset. RESULTS: Recanalization was accomplished in eight patients with intraarterial local thrombolysis; four of these patients had a good clinical outcome. Two factors characteristic of those whose treatment was successful were dramatic improvement of symptoms after partial recanalization achieved within 3 hours of onset and stabilized improvement after subsequent percutaneous transluminal angioplasty or carotid endarterectomy for residual atherosclerotic stenosis at the ICA origin. CONCLUSION: The results of this study suggest that urgent intraarterial local thrombolysis may be a successful treatment method for some patients in this critical clinical category if the treatment can be accomplished within 3 hours of ictus and followed by either angioplasty or endarterectomy for residual stenosis.

Aged↗