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Biomedical subjects

S Okawa

Publications and source records attributed to S Okawa.

At least 37 records · Page 2Linked to original sources
PubMed1990

[Grinding of titanium. 1. Commercial and experimental wheels made of silicon carbide abrasives].

Cast titanium was ground with commercial and experimental wheels made of silicon carbide abrasives, and their grinding performance was investigated. With the vitrified wheels made of the GC abrasive, at a higher the wheel circumferential speed and heavier the grinding pressure, the cutting rate was greater, accompanied by violent wear of the wheel. Being independent of the wheel speed, the grinding ratio reached about 1 under pressure heavier than 100 gf. The MgO-MgCl2-bonded wheels of the C abrasive exhibited a similar tendency. The manner in which the wheel was moved over the work during grinding proved to be very important, compared with the Ni-Cr alloy as reported previously. Only depression of the wheel against the work resulted in chemical attrition of the abrasive and discoloration of the work surface, or grinding burn, due to oxidation of titanium. Even when the wheel was moved over the work, chip-formation process of the cutting edge was far from ideal, and the work surface was contaminated due to reaction of titanium with the abrasive. At a higher wheel circumferential speed, more chips were loaded or built-up in the wheel and strongly rubbed the work surface, resulting in violent wear of the wheel; loading and dislodging of such chips were repeated.

Carbon↗
PubMed1990

[Grinding of titanium. 2. Commercial vitrified wheels made of alumina abrasives].

Cast titanium was ground with commercial vitrified wheels made of alumina abrasives, and their grinding performance was investigated. For cutting, the appropriate circumferential speed of the alumina wheels was about 700 m/min. A speed lower or higher than this yielded unfavorable grinding results, which were attributed to wheel loading or chemical attrition of the abrasive, respectively. The hard wheel made of the A abrasive was suitable for grinding of titanium, and moreover, the wheel of the WA abrasive was more suitable than that made of the A abrasive. Generally, the cutting rate of the alumina wheels was inferior to that of the silicon carbide ones investigated previously. Depression of the wheel against the work yielded unfavorable grinding results; the manner in which the wheel was moved over the work during grinding was very important, compared with the silicon carbide wheels. Although the wheel was moved over the work, the high circumferential speed of the wheel resulted in chemical attrition of the abrasive and discoloration of the work surface, or grinding burn. The grinding burn layer mainly consisted of a few microns-thick titanium oxide.

Aluminum Oxide↗
PubMed1990

[Determination of titanium flow by the tracer element molten method in the dental precision casting. 1. The principle of flow visualization and application to simple castings].

The tracer element molten (TEM) method has been developed for flow visualization of molten Titanium in dental precision casting. The principle of this technique is as follows. When Titanium is cast, the tracer element wire inserted previously into the selective point of the sprue is molten little by little and distributed according to the molten Titanium flow in the mold cavity. After solidification, to observe the flow pattern, the tracer element needs to be analyzed on a section of the casting by EPMA equipped with the stage scan mapping system. This technique using Ag, Au, Pd or Pt as a tracer has been applied to some simple castings in shape and has been confirmed to be a very powerful technique for Titanium flow visualization in dental castings.

Dental Casting Technique↗
PubMed1990

[Reactions at the nonprecious metal-ceramic interface during porcelain firing. (3) A commercial alloy forming much Cr oxide during firing].

To examine the interface reaction between porcelain and a commercial Ni-Cr dental alloy (containing higher Cr and Mo) during porcelain firing, electron probe microanalyzer (EPMA) and X-ray diffraction have been used to characterize the interface which has emerged by means of selective dissolution of the alloy caused by a bromine-methanol solution. Much Cr oxide was formed at the early stage of firing, and remained in the reaction layer even if the holding time at 960 degrees C was up to 8 minutes. As a result, many Cr atoms diffused into the porcelain layer, most of which was found to form oxides through X-ray diffraction. Moreover, the porcelain layer nearest to the oxide layer was deduced to be modified seriously.

Chromium↗
PubMed1989

Layered structure of cast titanium surface.

The present study concerns the surface layered structure of the cast Ti. A commercial Ti was cast into a mold which was made of a phosphate-bonded Al2O3/SiO2 investment. Elemental analyses of the interfacial zone of the casting were made under an electron probe micro-analyzer. The interfacial zone was composed of four layers: the outermost reaction or casting burn layer, the second layer of an O-and Al-stabilized alpha case, the third layer in which Si, P, O, and C were inhomogeneously concentrated, and the fourth layer which consisted of acicular or plate-like crystals. It was observed that the larger the cast volume and the higher the mold temperature, the thicker became each layer and the coarser became the acicular grains. Probably, the layered structure was formed through decomposition of reducible species in the burnout investment and diffusion of the resulting elements into the casting.

Dental Casting Investment↗
PubMed1989

[Study on grinding of base metal alloys. 4. Constant pressure grinding of a Ni-Cr alloy with vitrified wheels].

The grinding techniques and the constituent element of vitrified wheels suitable for a 13% Cr-Ni dental casting alloy were determined. The lever-type grinding test machine used in the previous study was modified so that a work might be ground under a constant pressure as it moved reciprocally within a short stroke along the tangential direction of a rotating wheel. The grinding performance of two marketed wheels and eleven experimental wheels with different constituent elements was tested. Abrasive grains on the working surface of alumina wheel wore extremely due to abrasive attrition. Carborundum wheels proved to be more suitable for grinding of the comparatively soft Ni-Cr alloy. Not only depressing a wheel against a work but also moving the wheel over it with heavier pressure should be desired for the maximal grinding efficiency. The experimental carborundum wheels exhibited much the same performance as the marketed carborundum wheel under a less grinding pressure that 100 gf. Only the wheel of grain size #150 bonded with 19% binder wore obviously under the pressure of 150 or 200 gf and provided about two times the performance of the marketed wheel.

Aluminum Oxide↗
PubMed1989

[Study on grinding of base metal alloys. 5. Constant pressure grinding of a Ni-Cr alloy with electro-deposited wheels].

The grinding techniques and electro-deposited wheels suitable for a 13% Cr-Ni dental casting alloy were determined. The lever-type grinding test machine modified in the previous study was used to investigate the grinding performance of experimental wheels of CBN- and diamond-particles. Depression of the diamond wheel against the work yielded unfavorable grinding results. Not only depression of the wheel against it but also moving the wheel over it with a heavier pressure is desired for higher grinding efficiency and its durability. Probably, the undurability of this wheel is associated with abrasive attrition due to oxidation or some chemical reaction with the work. The CBN wheel had not been suitable for the Co-Cr alloy tested in the third paper, but it exhibited very excellent performance for grinding of the Ni-Cr alloy, even without being moved over the work. Although being high in cost, the CBN wheel may pay for the very high performance and its durability.

Chromium Alloys↗
PubMed1989

[Reactions at the nonprecious metal-ceramic interface during porcelain firing (2). A commercial alloy containing higher Cr and Si].

To clarify the interface reaction between porcelain and a commercial Ni-Cr dental alloy (containing higher Cr and Si) during porcelain firing, electron probe microanalyzer (EPMA), X-ray diffraction and X-ray fluorescence analysis have been used to characterize the interface which has emerged by means of selective dissolution of the alloy caused by a bromine-methanol solution. At the early stage of firing, tin oxides (SnO2), contained in the porcelain powder, were reduced to Sn metal and the resultant reduction layer was about 10 microns in thickness from the interface. Although in the beginning of firing some Cr oxides were formed at the interface, with increasing retention time (within a few minutes) at 960 degrees C, extremely low oxygen partial pressure caused reduction of even such products.

Air Pressure↗
PubMed1989

Clinical application of Hobel's high-risk pregnancy scoring system.

Hobel's high-risk pregnancy screening scoring system was applied to 1,000 deliveries prospectively to test the validity of the screening system. Our results showed that the incidence of high-risk neonates increased significantly as the risk scores during the prenatal and intrapartum periods increased. In this series, 57.7% of the patients belonged to the low-low risk group and 9.8% was classified as the high-high risk group. The incidence of high-risk neonates in the low-low risk group was 13.5% whereas it was 32.0% in the high-high risk group. Further, maternal hypocapnia during delivery was found to be closely related to the incidence of neonatal hyperbilirubinemia in this series and proper management of maternal ventilations during delivery could reduce the incidence of neonatal hyperbilirubinemia.

Cohort Studies↗
PubMed1988

Intraarterial digital subtraction angiography with carbon dioxide: superior detectability of arteriovenous shunting.

Intraarterial digital subtraction angiography (IADSA) with carbon dioxide (CO2) was performed on 41 patients with liver or renal diseases. CO2 produced no hypersensitivity reactions, and the pain or feeling of warmth was relatively mild compared with iodinated contrast media. Although the image quality of the arterial or capillary phase was inferior to that with iodinated contrast media, the detectability of arteriovenous shunting was excellent. IADSA with CO2 may become an effective method for detecting arteriovenous shunting which cannot be demonstrated with conventional angiography or DSA with iodinated contrast medium.

Adult↗
PubMed1983

Activation of platelets in cancer, especially with reference to genesis of disseminated intravascular coagulation.

Seventy-five cancer patients were evaluated on a scale of coagulation abnormalities related to DIC, one point given for each of the following criteria fulfilled and the score (0 to 4) being used. 1. Platelet count less than 150 x 10(3)/mu 1. 2. PT prolonged more than 1 sec over control or APTT prolonged more than 10 sec over control. 3. Fibrinogen less than 250 mg/dl (mean fibrinogen value of the cancer patients minus 1SD). 4. FDP greater than or equal to 20 micrograms/ml. The patients were distributed with 27% for score 0, 38% for 1, 20% for 2, 7% for 3 and 8% for 4. Platelet mode volume in score 4 was smaller than that of the other groups. Platelet aggregation by epinephrine was decreased in score 3 and 4 (P less than 0.01), while it was increased in score 0 (P less than 0.05). ADP-induced aggregation was increased in score 0 and 1 (P less than 0.01 - 0.05). The mean value of beta-thromboglobulin in cancer patients (44 +/- 24 ng/ml) was significantly higher than that of control (22 +/- 13 ng/ml) (P less than 0.01). These results suggest the existence of hyperfunction of platelets in cancer patients and possibility of a triggering mechanism of such activated platelets in the genesis of DIC in cancer.

Adult↗