Biomedical subjects

Y Oshida

Publications and source records attributed to Y Oshida.

At least 19 recordsLinked to original sources

PubMed1997

Activities of liver pyruvate dehydrogenase complex and 3-hydroxyacyl-CoA dehydrogenase in sand rat (Psammomys obesus).

The sand rat (Psammomys obesus) is an animal model for non-insulin dependent diabetes mellitus, which is induced by a regular chow diet. The total activity of liver pyruvate dehydrogenase complex in the sand rats under normoglycemic and normoinsulinemic conditions was one half as high as that in the albino rats, but the activity of liver 3-hydroxyacyl-CoA dehydrogenase was more than 4 times greater in the former than in the latter, suggesting a low capacity for glucose oxidation and a high capacity for fatty acid oxidation in the sand rats. These metabolic conditions may be related to the predisposition of the animals towards diabetes. Diet-induced diabetes in the sand rats resulted in decreasing the active form of liver pyruvate dehydrogenase complex and in increasing the activity of liver 3-hydroxyacyl-CoA dehydrogenase, suggesting that the diabetic conditions further suppress glucose oxidation and promote fatty acid oxidation.

3-Hydroxyacyl CoA Dehydrogenases↗

PubMed1997

Effects of aging on the activities of pyruvate dehydrogenase complex and its kinase in rat heart.

Effects of aging on the activities of heart pyruvate dehydrogenase complex and pyruvate dehydrogenase kinase were examined using 7, 35 and 60 wk old rats. Aging did not affect the total activity of pyruvate dehydrogenase complex but decreased the activity state (percentage of active form) of the complex in rats under the fed condition (52%, 36% and 26% for 7, 35 and 60 wk old rats, respectively). This decrease in the complex activity with aging was suggested to be associated with an age-related decrease in the blood glucose disposal. Starvation for 24 h decreased the activity state to less than 3% in all of the age groups. The activity of pyruvate dehydrogenase kinase associated with the complex was not related to the alteration in the activity state of the complex; the kinase activity was slightly lower in 60 wk old rats than in the younger rats under the fed condition and activation of the kinase by starvation was greater in the younger rats. The mechanism for the decrease in activity of pyruvate dehydrogenase complex was discussed on the basis of glucose and fatty acid utilization of heart muscle cells.

Aging↗

PubMed1997

Corrosion behavior of 2205 duplex stainless steel.

The corrosion of 2205 duplex stainless steel was compared with that of AISI type 316L stainless steel. The 2205 stainless steel is a potential orthodontic bracket material with low nickel content (4 to 6 wt%), whereas the 316L stainless steel (nickel content: 10 to 14 wt%) is a currently used bracket material. Both stainless steels were subjected to electrochemical and immersion (crevice) corrosion tests in 37 degrees C, 0.9 wt% sodium chloride solution. Electrochemical testing indicates that 2205 has a longer passivation range than 316L. The corrosion rate of 2205 was 0.416 MPY (milli-inch per year), whereas 316L exhibited 0.647 MPY. When 2205 was coupled to 316L with equal surface area ratio, the corrosion rate of 2205 reduced to 0.260 MPY, indicating that 316L stainless steel behaved like a sacrificial anode. When 316L is coupled with NiTi, TMA, or stainless steel arch wire and was subjected to the immersion corrosion test, it was found that 316L suffered from crevice corrosion. On the other hand, 2205 stainless steel did not show any localized crevice corrosion, although the surface of 2205 was covered with corrosion products, formed when coupled to NiTi and stainless steel wires. This study indicates that considering corrosion resistance, 2205 duplex stainless steel is an improved alternative to 316L for orthodontic bracket fabrication when used in conjunction with titanium, its alloys, or stainless steel arch wires.

Chromium↗

PubMed1997

Titanium-porcelain system. Part II: Bond strength of fired porcelain on nitrided pure titanium.

Commercially pure titanium (CPT) substrate was subjected to porcelain firing and bond strengths under three-point bending mode (span length: 15 mm; crosshead speed: 0.5 mm/min) were evaluated. Experimental variables included surface treatments of CPT and porcelain firing schedules. Variables for the surface treatments were (1) sandblasting, (2) mono- and triple-layered nitridation, and (3) mono-layered chrome-doped nitridation. Variables for the porcelain firing schedule included (4) bonding agent application, (5) bonding agent plus gold bonding agent application, and (6) Procera porcelain application. All together eleven sample groups were prepared with different combination of aforementioned experimental variables. Statistically all of them exhibited no significant differences. Hence, we employed two further criteria; (I) the minimum bond strength should exceed the maximum porcelain strength per se, and (II) the CPT substrate should not be heated close to the beta-transus temperature. After applying these criteria, it was concluded that mono-layered nitridation and mono-layered application of chrome-doped nitridation on both (with and without) sandblasted and non-sandblasted surfaces were the most promising conditions for a successful Titanium-Porcelain System.

Dental Porcelain↗

PubMed1996

Effect of selected physical properties of waxes on investments and casting shrinkage.

This study evaluated the relationship between flow characteristics, bending strength, and softening temperature of paraffin and dental inlay waxes to casting shrinkage when patterns were invested with a phosphate-bonded investment. This study found that the casting shrinkage decreased as the flow of the wax pattern increased. If a low flow wax is used or if there is a need for a thick pattern, the size of the casting ring should be increased. When wax patterns are formed for cast restorations, it is important to select the type of wax with the most desirable properties for the margin and the occlusal portions. Moreover, to accurately fabricate castings, it is necessary to understand the physical properties of the chosen waxes.

Chemical Phenomena↗

PubMed1996

Effect of light exposure on fracture toughness and flexural strength of light-cured composites.

OBJECTIVES: This study was conducted to investigate the curing characteristics of light-cured composites and their related mechanical properties. METHODS: Single-edge notch specimens [25 mm x 2.5 mm x 5 mm with a 5 mm notch (a/W = 0.5)] were prepared for fracture toughness measurements. For flexural strength testing, a stainless steel mold (25 mm x 2 mm x 2 mm) was used. Light-cured composites were condensed into the mold, and the middle third of the specimen was first activated for 30 s with 400 mW/cm2, for 60 s with 200 mW/cm2, or for 120 s with 100 mW/cm2. Then the remaining thirds were activated at the same intensity and curing time as the middle third. After 24 h storage in 37 degrees C water, three-point bending tests were performed with a span length of 20 mm at a crosshead speed of 0.5 mm/min. A one-way ANOVA, followed by a Newman-Keuls test (p < 0.05), were used to compare the data obtained from each group to test the effect of the curing conditions. RESULTS: Fracture toughness, flexural strength, and flexural modulus varied with resin composites. Among the three curing conditions for each material, there were no significant differences in fracture toughness, flexural strength, or flexural modulus. SIGNIFICANCE: The fracture toughness and the flexural strength were the same when irradiations with the same amount of energy (light intensity multiplied by curing time) were used. It was found that, at lower light intensity, longer curing was required to provide comparable mechanical properties. An accumulated irradiation energy obtained through a product of the light intensity and curing time may serve as a guideline to produce samples exhibiting equivalent fracture toughness as well as flexural strengths.

Analysis of Variance↗

PubMed1996

Effect of C-peptide administration on whole body glucose utilization in STZ-induced diabetic rats.

Recent studies suggest that C-peptide stimulates glucose transport in isolated skeletal muscle. In order to determine the effect of C-peptide on whole body glucose utilization, streptozotocin (60 mg kg-1) (STZ)-induced diabetic and normal rats were studied using the euglycaemic clamp procedure and continuous infusion of somatostatin (1.0 micrograms kg-1 min-1) in pentobarbital-anaesthetized rats. Plasma insulin levels during the 6.0- and 30.0-mU kg-1 min-1 insulin infusions rose to 70-90 microU mL-1 and 500-700 microU mL-1, respectively. Blood glucose concentrations were clamped at 7.5-7.9 mmol L-1 in the diabetic rats and at basal levels or 7.7 mmol L-1 in the non-diabetic (normal) rats. Biosynthetic human C-peptide (0.5 nmol kg-1 min-1) was infused in 12 diabetic and 11 normal rats, resulting in concentrations of 26-41 nmol L-1. The metabolic clearance rate of glucose (MCR) for the diabetic rats receiving C-peptide (12.0 +/- 1.0 mL kg-1 min-1) was significantly (P < 0.01) higher than that in the diabetic rats given saline (6.3 +/- 0.7 mL kg-1 min-1) or a randomly scrambled C-peptide (7.8 +/- 1.3 mL kg-1 min-1) at low-dose insulin infusion but not at the high-dose insulin infusion. In normal rats C-peptide did not significantly increase the MCR for glucose. These results thus demonstrate that C-peptide has the capacity to increase glucose utilization in STZ-induced diabetic rats.

Animals↗

PubMed1996

Exercise training prevents maturation-induced decrease in insulin sensitivity.

We examined the effects of exercise training initiated before maturation or after maturation on insulin sensitivity and glucose transporter GLUT-4 content in membrane fractions of skeletal muscle. Female Wistar rats (4 wk of age) were divided into sedentary and exercise-trained groups. At 12 wk of age, a subset of the trained animals (Tr) was killed along with a subset of sedentary controls (Sed). One-half of the remaining sedentary animals remained sedentary (Sed-Sed) while the other half began exercise training (Sed-Tr). The remaining rats in the original trained group continued to train (Tr-Tr). Euglycemic clamp (insulin infusion rate at 6 mU.kg body wt-1. min-1) was performed at 4, 12, and 27 wk. After euglycemic clamp in all animals except the 4-wk-old, hindlimb (gastrocnemius and part of quadriceps) muscles were removed for preparation of membrane fractions. In sedentary rats, glucose infusion rate (GIR) during euglycemic clamp was decreased from 15.9 mg.kg-1.min-1 at 4 wk of age to 9.8 mg.kg-1.min-1 at 12 wk of age and 9.1 mg.kg-1.min-1 at 27 wk of age. In exercise-trained rats, the GIR was not significantly decreased by maturation (at 12 wk) and further aging (at 27 wk). Initiation of exercise after maturation restored the GIR at 27 wk of age to the same levels as these for the corresponding exercise-trained rats. GLUT-4 content in plasma and intracellular membrane fractions of hindlimb muscle obtained just after euglycemic clamp showed the same trend as the results of GIR. These results suggest that exercise training prevented the maturation-induced decrease in insulin sensitivity. Improvement of insulin sensitivity caused by exercise training was attributed, at least in part, to the increase in insulin-sensitive GLUT-4 on the plasma membrane in skeletal muscle.

Age Factors↗

PubMed1996

Trial production of titanium orthodontic brackets fabricated by metal injection molding (MIM) with sintering.

Safety and esthetics are two indispensable factors to consider when fabricating orthodontic brackets. However, these factors are not easily achieved when conventional techniques (including forging and casting) are used in the mass production of titanium brackets, albeit the brackets exhibit excellent biocompatibility. In the present study, orthodontic brackets were manufactured by metal powder injection molding with sintering. Brackets with three different base designs were made and subjected to compression shear tests for evaluation of their bonding strength to enamel substrate. The shapes given to the dimple of the base were spherical, oval, and grooved. The maximum shear forces for each type were 11.1 kgf, 7.6 kgf, and 18.5 kgf, respectively. The bonding strengths of the titanium bracket were equivalent to those obtained with conventional stainless steel brackets. Moreover, uniform distribution of Vickers hardness values (average, 240 +/- 40 Hv) measured at three locations indicated that the titanium bracket was uniformly sintered. Accordingly, titanium brackets thus fabricated exhibit a potential for clinical application.

Analysis of Variance↗

PubMed1996

Dentin bonding system. Part I: Literature review.

Currently, clinicians face choices of restoration including amalgams (mercury-based, gallium-based alloys, or mercury-free silver-based substitutes), composite resins, ceramics, and gold alloy. In order to choose an appropriate restorative material, many parameters are involved; they include preparation time requirements, finishing and polishing, marginal integrity, anatomy and contours, chipping and fracture, sensitivity, microleakage, wear resistance, and corrosion resistance. It is generally believed that amalgams are still evaluated as the best of all restorative materials as far as the aforementioned parameters are concerned. It is claimed that the amalgams exhibit in the range of 10 to 25 service years, while the composite resin exhibits ranging between 7 and 11 service years. When a composite resin requires a mass large enough for indirect fabrication, a bonding system is demanded with which this restoration should form an instantaneous, impervious, and stable bond to the tooth structure. Roughly a quarter century has passed since the research and development of a promising dentin bonding system was initiated. We are now in the fifth generation of the dentin bonding system, during the research and development of which various types of bonding agents as well as bonding models have been introduced. In this article, the history of development of the bonding agents and the understanding of the bonding mechanism will be reviewed.

Composite Resins↗

PubMed1996

Dentin bonding system. Part II: Effect of crosshead speed.

Dentin bond strengths are normally evaluated by conducting mechanical tests in tensile and/or shear mode at a certain level of crosshead speed. According to the literature review, crosshead speed is varied in a relatively wide range from 0.1 mm/min to 10.0 mm/min (with the exception of a few studies conducted above 10.0 mm/min). It was also found that crosshead speeds of 0.5, 1.0, 2.0 and 5.0 mm/min were commonly employed to evaluate dentin bond strengths for both tensile and shear modes, although no rationale for selecting the crosshead speed was described in the articles. For testing dentin bond strengths, no plastic deformation should be involved, and fracture only should take place during the fracturing process. With the Scotchbond Multiple-Purpose/Z100 bonding system, tensile bond strengths were evaluated at crosshead speeds of 0.1, 0.5, 1.0, 5.0 and 10.0 mm/min. It was found that (i) there was no strain rate sensitivity when the test was conducted below the 1.0 mm/min crosshead speed, and (ii) if the crosshead speed exceeded 1.0 mm/min, a strain rate dependency of the tensile bond strengths was observed. Knowledge that the composite resin (Z100) did not exhibit strain rate dependency influenced the conclusion that (iii) the above observed strain rate dependency was solely due to the mechanical response from the bonding interface region.

Bias↗

PubMed1995

A clinical survey on the compliance of exercise therapy for diabetic outpatients.

To clarify the present state of exercise therapy for diabetes mellitus, we conducted a survey of 570 diabetic outpatients by written questionnaires. The results revealed that approximately 30% of the patients did not implement the prescribed exercise regimen. The principal reasons for low compliance were 'lack of time to do' and 'lack of mind to do'. 'Lack of time to do' was particularly numerous in male patients. Other reasons were 'lack of guidance by physician', 'lack of interest', 'lack of understanding of procedure'. These findings indicated that the patients should be motivated adequately when they are diagnosed as having diabetes and subsequently encouraged to reinforce their intentions by the physician and co-medical staff. Furthermore, they showed that specific approaches suitable for each individual patient and not standardized guidelines should be devised. As regards the daily environment of patients, the cooperation of the patient's family would be effective and the exercise facilities and the exercise guidance personnel should be augmented.

Diabetes Mellitus↗

PubMed1995

Effect of daily voluntary running on in vivo insulin action in rat skeletal muscle and adipose tissue as determined by the microdialysis technique.

The effect of physical training on in vivo insulin-stimulated glucose utilization in relation to glycolysis (lactate formation) in rat peripheral tissues was investigated in 8 sedentary controls (SC) and 7 voluntary running rats (VR). We used a sequential euglycemic clamp procedure (insulin infusion rate; 6.0, 30.0 mU/kg.min) in combination with a microdialysis technique in M. quadriceps femoris, vastus lateralis, and inguinal adipose tissue. In the clamp study, glucose infusion rate (GIR) averaged over 45-75 min during the 6.0-mU/kg.min insulin infusion was significantly (p < 0.01) higher in VR (15.36 +/- 0.83 mg/kg.min, mean +/- SE) than in SC (10.41 +/- 0.88 mg/kg.min), and the lack of a significant difference in GIR between VR and SC was found during the 30.0-mU/kg.min insulin infusion. In these tissues, there was no significant difference in dialysate lactate levels between VR and SC in the basal state without insulin or glucose infusion, or at an insulin infusion rate of 30.0 mU/kg.min. However, dialysate lactate concentrations in muscle averaged over 45-75 min during the 6.0-mU/kg.min insulin clamp procedure in VR (8.51 +/- 0.71 mg/dl) were significantly (p < 0.05) higher than in SC (6.18 +/- 0.48 mg/dl). These results indicated that insulin action in skeletal muscle and adipose tissue could be evaluated in vivo by using the microdialysis technique, and that an increase in GIR in VR was, in part, explained by an increase in lactate formation in skeletal muscle.

Adipose Tissue↗

PubMed1995

Development of photo-sensing bulge ductility tester.

The ductility of thin films is normally evaluated by conducting the bulge testing. However, the accuracy of the conventional type of mechanical bulge ductility testing unit is poor in determining the actual elongation. In this development, a photo-sensitive device is provided in the detecting portion to accurately measure the elongation. The sensitivity depends on the type of the materials tested. A Pyrex glass ball is utilized as a punching ball to provide equally distributed light. Pushing of the Pyrex glass is activated by a hydraulic media to control the punching velocity. Accuracy and reproducibility were primarily checked with copper thin foil deposited on polyimide substrates. Two types of dental articulating papers (paper-based and plastic-based) were tested. It was suggested that an appropriate selection of articulating paper to mark the occlusal interferences is essential for precise determination of occlusal harmony.

Dental Materials↗

PubMed1995

Some mechanistic observation on water-deteriorated dental composite resins.

Four different types of dental composite resins were subjected to the water sorption environment in both dyed and undyed distilled water for 1 and 5 weeks at 37 degrees C. Weight changes due to the water sorption, effects of water sorption on mechanical properties, and fractographic observations were conducted. It was found that (i) the water sorption was diffusion-controlled, (ii) both break stress and modulus of elasticity reduced by increasing the amount of absorbed water, and (iii) fractographic observations showed that fracture pattern of the wet/dry/wet lamellar structure was not straight line, rather S-shaped pattern, suggesting that (a) mechanical properties (particularly, the modulus of elasticity) of the wet portion were not same as those in the dry portion, and (b) there could be an internal residual stress developed at/in the interfacial zone between the dry and wet portion. By one-layer removal from the wet/dry/wet lamellar structure composites, the residual stress was calculated from measuring the radius of the curvature. It was found that for all water-sorbed composite materials, tensile residual stresses were developed, which were from 30 to 40% of the break stresses for TPH, Charisma, and Durafil VS, and was 78% of the break stress for Z100 material.

Composite Resins↗

PubMed1994

Experimental development of a chitosan-bonded beta-tricalcium phosphate bone filling paste.

Bone filling substances are needed to meet several requirements including nontoxicity, setting time, changes in pH values, and amount of dissolved elements as well as mechanical properties. In this study, the bone-generating composites were prepared by employing the in vivo absorbable beta-tricalcium phosphate as a parent matrix kneaded with CaO, MgO, and ZnO as bone mineral additives with different compositions. The setting time, pH values, compressive strength were investigated as a function of the amount of these bone mineral additives. It was found that the setting time was shortened by increasing CaO, MgO, and ZnO contents. Increasing ZnO contents resulted in the pH value lower, while the pH values increased by increasing CaO and MgO contents. Increasing ZnO contents caused the compressive strength stronger, on the other hand, the compressive strength was weakened by increasing MgO contents. Furthermore, calcium appears to be selectively released from the hardened composite sample.

Analysis of Variance↗

PubMed1994

Fractal dimension analysis of mandibular bones: toward a morphological compatibility of implants.

In addition to biological and mechanical compatibilities for promising implant materials, a morphological compatibility is proposed by the authors. It has been reported by many investigators that implant surface with appropriate roughness and pore size exhibit better bone ingrowth activities. However, these parameters cannot characterize the complexity of surface textures. In the present study, dentulous and edentulous mandibular alveolar bones were utilized. Four segments from each mandible were subjected to the Fractal Dimension (DF) analysis. It was found that the dentulous mandible showed the DF of 1.81 +/- 0.03 while the edentulous mandible exhibited DF of 1.55 +/- 0.07, indicating that the former has more complex surface texture. It was also found that there could be a linear relationship between the surface roughness and the fractal dimension.

Alveolar Process↗

PubMed1993

Anodic polarization behavior and microstructure of a gallium-based alloy.

A gallium-based alloy (GA) that was developed as a substitute for dental amalgam was investigated for anodic polarization behavior in deoxygenated Ringers solution, 37 degrees C. The related microstructures were examined and microanalyses were conducted. Four polarization tests were conducted by scanning from -300mV to +1,000 mV (vs. SCE) at 2 mV/s. Polarization of the first sample (GA-1) was stopped after the first anodic dissolution peak (-100 mV, 1.5-2.0 x 10(-3) A/cm2). The fourth sample (GA-4) was interrupted at the secondary peak (+1000 mV, 0.3 A/cm2). It was found that (1) the early stage of the first peak is related to selective dissolution of divalent tin ions, followed by a dissolution of Ga. Transmission electron diffraction (TED) identified the brown corrosion product as Ga2O3; (2) the GA-4 sample was covered with the white corrosion product of mainly Sn+4, identified as SnO2. In addition, the current density of the GA sample when coupled with a high-copper dental amalgam was 0.03 A/cm2 (with +1,000 mV) at the second peak which was about a ten times lower value than for the uncoupled sample; (3) the uncoupled gallium alloy and gallium alloy coupled with a high-copper dental amalgam showed 10(3)-10(4) times higher anodic current density than that of an uncoupled high-copper dental amalgam, suggesting that the gallium alloy is more corrosion prone.

Corrosion↗