Biomedical subjects

K Asaoka

Publications and source records attributed to K Asaoka.

At least 73 records · Page 4Linked to original sources

PubMed1994

Behavior of a calcium phosphate cement in simulated blood plasma in vitro.

OBJECTIVES: The purpose of this study was to gain a better understanding of the integration of calcium phosphate cement (CPC) implants in biological tissue. METHODS: An in vitro continuous flow system was employed to examine the protracted behavior of disc-shaped specimens of this bioactive material under sustained physiological-like solution conditions. Weight measurement, diameteral tensile strength measurement (DTS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and powder x-ray diffraction (XRD) were used to characterize the CPC samples as a function of immersion time. RESULTS: When CPC was immersed in simulated blood plasma in which the Ca (2.5 mmol/L) and inorganic phosphate (1.0 mmol/L) levels were kept constant, both the weight and DTS of the specimens steadily increased to about 1.5 times their original values over a period of 20 wk. SEM observations showed new precipitate formations in intimate contact with the original CPC surface. FTIR and XRD analyses revealed that the precipitate was a B-type carbonate hydroxyapatite (OHAp), the type of OHAp observed in bone and dentin. On the other hand, the interior of CPC discs did not show an increase in either bulk density or OHAp content. Thus, the increases in weight and DTS are attributable to the OHAp precipitation on the CPC surface. SIGNIFICANCE: The results suggest that under in vivo conditions, CPC implants would not dissolve in physiological fluids. OHAp coatings may form on the implants, which may enhance bonding of implants to bone by mechanically strengthening the interface between them.

Biocompatible Materials↗

PubMed1994

Occlusion of dentinal tubules with calcium phosphate using acidic calcium phosphate solution followed by neutralization.

The occlusion of dentinal tubules with calcium phosphate, by a calcium phosphate precipitation method (CPP method), was investigated in vitro for evaluation of the potential value of this method for the treatment of dentin hypersensitivity. The method consists of treating the dentinal surface with a CPP solution, i.e., an acidic solution that contains both calcium and phosphate, followed by neutralization with basic post-treatment solution. The CPP solutions used in this study ([Ca] = 0.2 - 1.0 mol/L, [PO4] = 0.2 - 4.0 mol/L) were prepared by dissolving Ca(OH)2 or CaHPO4 x 2H2O in H3PO4 or HCl, and 1 mol/L NaOH solution was used for the post-treatment solution. Sections of human dentin disks treated by the CPP method were observed by scanning electron microscopy, and the precipitate in the dentinal tubules was subjected to x-ray micro-analysis. After treatment by the CPP method, dentinal tubules were occluded to a distance of approximately 15 microns from the surface, and the precipitate showed a Ca/P molar ratio of 1.03 +/- 0.01 To obtain a larger amount of precipitated mineral for further analysis, we used the same procedure with glass tubes (inside diameter, 1 mm). Powder x-ray diffraction analysis and FT-IR measurement revealed that the precipitate was dicalcium phosphate dihydrate (CaHPO4 x 2H2O). The instant precipitation of calcium phosphate mineral in the dentinal tubules demonstrated the potential value of the CPP method for the occlusion of dentinal tubules, this occlusion may be useful for the treatment of dentin hypersensitivity.

Calcium Phosphates↗

PubMed1994

Effects of creep value and occlusal force on marginal adaptation of amalgam filling.

Creep of amalgam is thought to be a factor determining poor marginal adaptation. Clarification of the relationship between creep of amalgam in the cavity and creep value (American Dental Association specification no. 1; ADA #1) is essential to an understanding of the mechanism of marginal fracture and service life. However, only elastic stress analyses of amalgam in a cavity have been reported in the dental field. Therefore, the creep of amalgam in a class I cavity was simulated by an axisymmetric elastic creep finite-element method. The stress and time dependencies of the creep rate of amalgam were incorporated into this calculation. Creep values of 1.0 and 3.0% (ADA #1) were selected as amalgam properties. When the occlusal force on the amalgam filling was assumed in the vertical direction along the axis of the tooth, the rate of extrusion and rate of opening of the gap at the cavity margin were revealed by the simulation. The computed results show that the gap and extrusion were developed in direct proportion of the creep value and proportionally with the square of the occlusal force. Simulated results are in agreement with clinical findings of the service lives of restorations, i.e., a poor adaptation to the margin can be seen for 4-to-10-year-old amalgam fillings.

Bite Force↗

PubMed1994

Temporary neurological deterioration caused by hyperperfusion after extracranial-intracranial bypass--case report and study of cerebral hemodynamics.

A 64-year-old female with occlusion of the left internal carotid artery (ICA) developed temporary neurological deterioration after superficial temporal artery to middle cerebral artery anastomosis. Preoperative single photon emission computed tomography (SPECT) showed marked reduction of the cerebral perfusion reserve in the left ICA territory. She suddenly developed aphasia 18 hours after operation. Follow-up SPECT revealed temporary hyperperfusion in the left temporal lobe, strongly suggesting that this unusual complication resulted from bypass flow into the brain tissue with chronic severe ischemia and impaired autoregulation.

Aged↗

PubMed1994

Effect of leucite crystals on the strength of glassy porcelain.

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.

Aluminum Silicates↗

PubMed1994

Diffusion of elements in porcelain into titanium oxide.

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.

Barium↗

PubMed1994

Effect of calcium ions on hydroxyapatite formation from the hydrolysis of anhydrous dicalcium phosphate.

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 (2.5 mmol DCPA/250 mL) were carried out at fixed pH in the absence or presence of CaCl2 (0-200 mmol/L) by standard pH stat techniques at 37 degrees C. The rate of hydrolysis was much faster, and the yield of HAP approximately doubled in the presence of CaCl2 when compared to no CaCl2, but no significant difference was observed over the range of Ca2+ concentrations examined (25-200 mmol/L). At equivalent conversion times, the crystallinity of the HAP formed was also greater in the presence of CaCl2. Calculations showed that much less DCPA dissolved to reach solution equilibrium with respect to HAP in the presence than in the absence of CaCl2. We conclude, therefore, that solution Ca2+ is an important factor in controlling HAP formation from the hydrolysis of acidic calcium phosphates such as DCPA.

Calcium↗

PubMed1994

Effect of crystallization on fracture strength of castable glass-ceramics containing two crystals.

The relationship between fracture strength and crystallization in castable glass-ceramics was studied using castable glass-ceramics which contained crystalline apatite and magnesium titanate. Bending strength was increased with increases in crystal phases; 90, 124, 122 and 162 MPa were recorded for as-cast specimens and specimens cerammed at temperatures of 905 degrees, 925 degrees and 945 degrees C, respectively. The results of bending tests suggest that the crystallization of magnesium titanate is more effective than that of apatite in increasing the strength of glass-ceramics. Fracture toughness in specimens reheated at 905 degrees C was doubled compared with as-cast specimens. The apatite particles precipitated during ceramming treatment were thought to be an important factor in increasing both the fracture toughness and crack pinning effect.

Apatites↗

PubMed1994

[Angiographic examination of the vertebral artery at the atlantoxial joint during head rotation].

Stenosis or occlusion of the vertebral artery at the atlantoaxial joint associated with head rotation is generally considered an uncommon cause of vertebrobasilar insufficiency. This rotational contralateral (to the face) vertebral artery occlusion is considered to be a "physiological phenomenon". The purpose of the present article is to investigate whether stenosis or occlusion of the vertebral artery at the atlantoaxial joint really occurs with head rotation. The authors performed vertebral angiography both in the neutral position and with contralateral rotation of the head (about 80 - 90 degrees) on 39 patients (44 vertebral arteries), who didn't have any disease of the cervical region or of the posterior cranial fossa. The authors discussed the angiographic findings concerning the vertebral artery at the atlantoxial joint during contralateral rotation of the head. In some cases a vertebral artery was stretched with head rotation. However occlusion or stenosis of the vertebral artery was never found to occur at the atlantoaxial joint level in any of the cases. This result indicates that rotational vertebral artery occlusion is not a "physiological phenomenon". There may be many other developmental and degenerative factors contributing to this rotational occlusion, such as atherosclerosis, kinking, and tortuosity of the vertebral artery, hyperosteosis, tightness of the paravertebral muscle, stenosis of transverse foramen and the depth of the vascular groove of the atlas.

Adult↗

PubMed1994

[Two cases of what was regarded as cerebral vasculitis].

Two cases of cerebral vasculitis of the central nervous system are reported. In our cases, systemic investigation found no underlying cause for vasculitis. Case 1: A 59-year-old female presented severe headache due to subarachnoid hemorrhage. CT scan obtained one month later demonstrated a low density area with ring-like enhancement in the right frontal lobe. A surgical specimen revealed inflammation of the leptomenigeal vessels with many lymphocytes. Case 2: A 64-year-old female came to us with dysarthria and slight left hemiparesis. CT scan and MRI obtained after admission demonstrated an abnormal mass lesion with enhancement in the right frontal lobe. The histological examination revealed vasculitis. After systemic disease and central nervous system infection were excluded, we diagnosed this case as cerebral vasculitis of unknown origin. In this paper, the clinical and pathological features of cerebral vasculitis and differential diagnosis were discussed.

Cerebrovascular Disorders↗

PubMed1994

[A case of bow hunter's stroke].

A case of vertebrobasilar insufficiency with vertigo and horizontal nystagmus induced by neck rotation is reported. This patient's angiography demonstrated obstruction of left vertebral artery at the Cl-2 level on right rotation of the head. Surgical decompression of the vertebral artery by partial transversectomy of the atlas vertebra in this case relieved the symptoms, and postoperative angiography demonstrated the disappearance of the vertebral artery occlusion at the neck rotation. The pathogenesis and treatment of vertebral artery occlusion at Cl-2 level are discussed.

Aged↗

PubMed1993

Congenital ankyloglossia with deviation of the epiglottis and larynx: symptoms and respiratory function in adults.

We operated on 38 adult patients with congenital ankyloglossia with deviation of the epiglottis and larynx. The results were as follows. 1) Most patients had Angle's class III malocclusion, irregular alignment of the upper teeth, and high hard palate. 2) Fifty percent of the patients in our study population had obstructive respiratory failure. Their vital capacity increased significantly after the operation, but changes of forced expiratory volume in 1 second were not prominent. 3) Subjective symptoms of this disease were stiffness of the shoulders, a cold feeling in the extremities, an obstructed feeling in the throat, insomnia, fatigue, dry skin, irritability and/or anxiety, and nervousness. These improved postoperatively. 4) Objective symptoms included snoring, muscle cramps, difficulty in playing wind instruments, hoarseness, and incorrect articulation. The objective symptoms, except for incorrect articulation, improved postoperatively.

Adult↗

PubMed1993

Purification from liver microsomes from untreated cynomolgus monkeys of cytochrome P450 closely related to human cytochrome P450 2B6.

A cytochrome P450 (P450) (referred to as P450CMLa) was purified and characterized from hepatic microsomes from untreated cynomolgus monkeys (Macaca irus). The final preparation was electrophoretically homogeneous and its estimated minimum molecular mass was 49.5 kDa. The amino-terminal amino acid sequence of the protein (first 34 residues) closely resembled that of the protein encoded by the 2B6 cDNA from humans (94%). This protein was cross-reactive with antibodies raised against P450 2B1 (P450 b), P450 2B11 (P450 PBD-2), and P450GP-1, which were purified from hepatic microsomes from phenobarbital-pretreated rats, beagle dogs, and guinea pigs, respectively. Also, the antibody raised against P450CMLa was able to cross-react with P450 2B1, P450 2B11, and P450GP-1. P450CMLa was capable of catalyzing benzphetamine N-demethylation and testosterone 16 beta-hydroxylation in a reconstituted system. Anti-P450CMLa antibody inhibited the activity of testosterone 16 beta-hydroxylase but not the activities of testosterone 2 beta- and 6 beta-hydroxylases in liver microsomes from cynomolgus monkeys. The content of P450CMLa, as estimated by immunoblot analysis, was 70 pmol/mg (about 5% of total P450). The protein immunoreactive with the anti-P450CMLa antibody was also present in liver microsomes from Japanese monkeys, baboons, common marmosets, and common squirrel monkeys. In liver microsomes from common squirrel monkeys, the content of protein immunoreactive with the anti-P450CMLa antibody and the activity of testosterone 16 beta-hydroxylase were effectively increased by pretreatment with phenobarbital. The antibody against P450CMLa strongly inhibited the activity of testosterone 16 beta-hydroxylase in liver microsomes not only from untreated cynomolgus monkeys but also from phenobarbital- and pregnenolone 16 alpha-carbonitrile-pretreated common squirrel monkeys. These results indicated that the P450CMLa purified here is very similar to the forms of P450 classified into the 2B subfamily, in its amino-terminal amino acid sequence, catalytic activities, and immunochemical properties.

Amino Acid Sequence↗

PubMed1992

Digit sucking.

Explore the source record for details and available documents.

Female↗

PubMed1992

Influence of tempering method on residual stress in dental porcelain.

The porcelain component of a porcelain-fused-to-metal restoration is strengthened by residual (tempering) stresses which are induced by cooling procedures followed in dental laboratories. The thermophysical properties of materials and cooling rate are the main factors which determine the residual stress. In this paper, the temperatures in the midplane of body-porcelain disks were measured from a heat-soak temperature (1000 degrees C) to room temperature during two different cooling procedures: slow cooling in air and forced-air cooling. Experimental results approximated exponential cooling wherein the cooling rates could be represented by a linear equation of temperature. Residual stresses, as affected by the tempering method and thickness of a porcelain disk, were calculated by computer simulation for regions away from the edges. The following temperature-dependent factors were incorporated into the simulation: elastic modulus, viscosity, and coefficient of thermal expansion. The cooling rate dependencies of the glass transition temperature and the temperature distribution during cooling were also included. The cooling rates used in this simulation were derived from the tempering data. The agreement between development of transient and residual stresses--calculated by computer simulation for various cooling methods, and the tendency toward failures of porcelain disks subjected to the tempering processes--was examined. Simulated residual stresses were also in good agreement with those measured by the indentation fracture method of Marshall and Lawn (1977) and Anusavice et al. (1989).

Computer Simulation↗

PubMed1992

Pharmacological studies on 3-formylamino-7-methylsulfonylamino-6-phenoxy-4H-1-benzopyran-4-one (T-614), a novel antiinflammatory agent. 3rd communication: the involvement of bradykinin in its analgesic actions.

In order to elucidate the analgesic mechanism of 3-formylamino-7-methylsulfonylamino-6-phenoxy-4H-1-benzopyran-4-on e (T-614), its effects on the kinin-forming system were examined both in vivo and in vitro. T-614, at doses more than 10 mg/kg p.o., exhibited a significant inhibitory effect on the increased levels of bradykinin released into the pouch fluid of kaolin-induced inflammation in rats. In the kaolin-induced writhing response in mice, which is shown to be mainly dependent on the action of bradykinin, T-614 reduced not only the writhing frequency but also the peritoneal levels of bradykinin in a dose-dependent manner. Whereas, in the zymosan-induced writhing response in which prostaglandin I2 (PGI2) is shown to be an important mediator, it did not exert an obvious inhibition on either writhing responses or peritoneal PGI2 levels at a highest dose of 100 mg/kg. T-614 did not inhibit the activities of serine proteases, such as trypsin, thrombin, kallikrein and plasmin. Furthermore, it did not affect the kinin-forming enzymes of rat plasma in vitro. The above results suggest that the analgesic effects of T-614 may be partly mediated by the inhibition of bradykinin release in the local inflamed tissue.

Analgesia↗

PubMed1992

Pharmacological studies on 3-formylamino-7-methylsulfonylamino-6-phenoxy-4H-1-benzopyran-4-one (T-614), a novel antiinflammatory agent. 4th communication: inhibitory effect on the production of interleukin-1 and interleukin-6.

In vitro effects of 3-formylamino-7-methylsulfonylamino-6-phenoxy-4H-1-benzopyran-4-on e (T-614), a novel antiinflammatory compound, on the production of interleukin-1 (IL-1) and/or interleukin-6 (IL-6) by human monocytes and the THP-1 cells of a human monocytic cell line, were examined. T-614 inhibited the release of immunoreactive IL-1 beta from these cells stimulated with lipopolysaccharides (LPS) in a dose-dependent manner (0.3-30 micrograms/ml). The release of IL-6 from THP-1 cells, as determined by the assays for its hepatocyte-stimulating activities and immunoreactivities, was inhibited by T-614 with the IC50 values of 2.0 and 6.6 micrograms/ml, respectively. Northern blotting analysis using LPS-stimulated THP-1 cells indicated that the inhibitory effect of T-614 on IL-1 beta production is caused by the suppression of IL-1 beta mRNA expression. The inhibition of cytokine production by T-614 may provide an important insight into the additional mechanisms contributing to its antiinflammatory activities.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1992

Computer simulation on creep of amalgam in Class I cavity.

The creep behavior of amalgam in Class I cavity was simulated by an axi-symmetric elastic creep finite element method. In this procedure, the stress and time dependencies of the creep strain of amalgam were incorporated. Exponents of stress and time dependencies were postulated as 2.0 and 1.0, respectively. Amalgam with 1.0% of creep value (tested by American Dental Association Specification No. 1) were selected for the material to calculate. Simulation was conducted for the occlusal force of 40, 100, and 150 N, respectively, on the caps of enamel and vertical direction to the axis of the tooth. Results show that creep strain of amalgam in the cavity did not increase linearly with time because the amalgam deformed to become stress-free and creep rate was a function of the stress. It was concluded that elastic deformation of the crown with no filling material in its cavity is an important factor in determining the creep strain and the gap between the cavity and the restorative material.

Biomechanical Phenomena↗