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Biomedical subjects

K Asaoka

Publications and source records attributed to K Asaoka.

At least 55 records · Page 3Linked to original sources
PubMed1997

Influence of modification of Na2O in a glass matrix on the strength of leucite-containing porcelains.

The desirable thermal properties of matrix glass to the strength of feldspar porcelain with leucite crystal were investigated. Five kinds of feldspar glasses, each with different a content of Na2O, were prepared for the matrix glasses of the leucite-containing porcelains. The specimens were arranged by mixing each glass powder with high-purity natural leucite crystals (0, 20 and 40%) followed by firing. The thermal properties of the glass and the transformation temperature of the leucite were measured. A three-point bending test was performed to measure the flexural strength of the porcelains. The glass transition temperature and deformation temperature of the glass-only porcelains were decreased as the Na2O content increased. The Na2O-modified glasses were substantially strengthened by the leucite dispersion. However, the strength of the porcelains was affected by the relation between the transformation temperature of the leucite and the thermal properties of the glass matrix. It was concluded that control of the residual stress in the composite porcelain is an important factor in developing high strength porcelain containing leucite.

Aluminum Silicates↗
PubMed1997

Thermal diffusivity and specific heat of dental casting alloys at room and elevated temperatures.

Thermal diffusivity and specific heat of four groups of dental casting alloys (Ag-based, Au-Pd, high karat and Ni-based alloys) were determined. Measurements were carried out from room temperature to 750 degrees C in an evacuated electric furnace with a laser flash thermal constant analyzer. There was no significant difference between the values of thermal diffusivity in the Ag-based and high karat alloys; 18-24 and 40-53 mm2/s, at room temperature and at 600 degrees C, respectively. For Au-Pd and Ni-based alloys, diffusivity was 8-12 and 3-4 mm2/s at room temperature, and 19-22 and 5-6 mm2/s at 600 degrees C, respectively. The thermal diffusivity of the alloys was significantly low compared to that of the pure-metals of which they were composed. Specific heat was determined as 0.14-0.16, 0.24-0.34, 0.17-0.19 and 0.45-0.51 kJ/(kg.K) for high karat, Ag-based, Au-Pd and Ni-based alloys, respectively, at room temperature. Oxidation of the Ni-based alloy at elevated temperature affected the value of specific heat measured.

Dental Alloys↗
PubMed1997

[Single stage excision for an intractable brain abscess and free rectus abdominis flap for reconstruction of the anterior skull base].

A case is presented of the frontal brain abscess following resection of squamous cell carcinoma of the maxillary sinus who had undergone reconstruction of the anterior skull base using a free rectus abdominis muscle flap. Local flap, ex. galeal flap, can be used for separating the cranial space from the paranasal sinuses and the nasopharynx, but it cannot provide reliable separation and protection of the brain from bacterial flora of the upper airway and it is too weak to support the brain in cases where orbital exenteration has been performed. The distant flaps such as the pectoralis major musculocutaneous flap, on the other hand, can provide a good alternative for reconstruction of the anterior skull base in such difficult cases, but frequently requires a secondary division of the pedicle. The free flap can circumvent such problems. We used the free rectus abdominis muscle flap and the postoperative course was uneventful. A bone graft was not necessary to reconstruct the anterior skull base.

Brain Abscess↗
PubMed1996

Non-decay type fast-setting calcium phosphate cement: setting behaviour in calf serum and its tissue response.

Non-decay type fast-setting calcium phosphate cement (nd-FSCPC) was evaluated in terms of its setting behaviour in calf serum and its tissue response to investigate the feasibility of its clinical use in surgical applications. Non-decay type cements were prepared by adding various amounts of sodium alginate to the liquid phase of base cements, fast-setting calcium phosphate cement (FSCPC) and conventional calcium phosphate cement (c-CPC). Cement pastes were immersed in serum at 37 degrees C immediately after mixing, and decay behaviour, setting time and mechanical strength were measured to evaluate the possibility of their use in surgical applications. Also, nd-FSCPC was implanted into rat subcutaneous tissue for the initial evaluation of biocompatibility of this potential bioactive cement. nd-FSCPC set in approximately 6-7 min in serum, even when the cement paste was immersed in the serum immediately after mixing, whereas c-CPC and FSCPC decayed completely upon immersion. nd-FSCPC transforms to hydroxyapatite (HA) within 24 h and shows a diametral tensile strength of approximately 4-5 MPa. As a result of transformation to HA, nd-FSCPC showed excellent tissue response when implanted subcutaneously in rats. We conclude that nd-FSCPC has good potential value for use in orthopaedics, plastic and reconstructive surgery, and oral and maxillofacial surgery, where the cement is exposed to blood.

Animals↗
PubMed1996

Effects of hexafluorosilicate on the precipitate composition and dentine tubule occlusion by calcium phosphate.

OBJECTIVES: To improve the calcium phosphate precipitation (CPP) method for the occlusion of dentine tubules with calcium phosphate, the addition of calcium hexafluorosilicate (CaSiF6) to CPP solution was evaluated in vitro with respect to its occluding capacity and the composition of the precipitate. METHODS: The occlusion of dentine tubules was evaluated by SEM observations and by measurements of dentine permeability. The composition of the precipitate was determined by measuring the calcium to phosphorus (Ca/P) ratio of the precipitate in dentine tubules by energy dispersive X-ray spectroscopy (EDS). RESULTS: The addition of CaSiF6 to the CPP solution resulted in an increase of the Ca/P ratio in the precipitate not only on the dentine surface but also inside the dentine tubules; indicating that the precipitate became more apatitic in nature. The addition of CaSiF6 had no effect on occluding capacity in terms of measurements of dentine permeability or SEM observations. Dentine permeability decreased to approximately 4% of pretreatment values and the dentine tubules were occluded for approximately 10-15 microns from the dentine surface. CONCLUSION: It is concluded that the addition of CaSiF6 to CPP solution was desirable, since it provided a more apatitic precipitate in the dentine tubules, not only on the dentine surface but also inside the tubules, and there were no drawbacks with respect to its occluding capacity.

Apatites↗
PubMed1996

Fluoridation of hydroxyapatite powder by ammonium hexafluorosilicate.

Diamine silver fluoride [AgF: (NH3)2AgF] is a unique fluoride solution used clinically in Japan for primary teeth. AgF has been shown to reduce dental caries and dentine hypersensitivity. However, AgF also stains teeth black due to sulfide precipitation and thus is unacceptable for permanent teeth. In the present study, the potential value of ammonium hexafluorosilicate [SiF: (NH4)2SiF6], which has a formula similar to that of AgF but contains no Ag, was studied with respect to its ability to fluoridate apatite. Hydroxyapatite [HAP: Ca10(PO4)6(OH)2] powder was treated with several topical fluoride solutions, i.e. neutral sodium fluoride, acidulated phosphate fluoride (APF) along with AgF and SiF. Following treatment, the HAP powders were analyzed for their fluorine content, crystallinity changes, and solubility in acidic solution. The highest level of fluoridated HAP [FAP: Ca10(PO4)6(OH)xF2-x] was observed in HAP powder treated with SiF, even though more total fluorine in the form of FAP and CaF2 was observed in HAP powder samples treated with APF. Presumably as a consequence of this higher level of FAP formation after SiF treatment, the highest level of crystallinity along with the lowest solubility in acidic solution were observed in HAP powder treated with SiF solution. We concluded, therefore, that SiF may have potential value for use as a topical fluoride solution.

Acidulated Phosphate Fluoride↗
PubMed1996

Stereoselectivity in bunitrolol 4-hydroxylation in liver microsomes from marmosets and Japanese monkeys.

The stereoselectivity in 4-hydroxylation of bunitrolol (BTL), a beta-adrenoreceptor blocking agent, was examined in liver microsomes from monkeys (marmosets and Japanese monkeys) and compared with the results of human liver microsomes. The formation of (+)-4-OH-BTL from (+)-BTL from (+)-BTL was significantly higher than that of (-)-4-OH-BTL from (-)-BTL in the liver microsomal fractions from the two kinds of monkeys. The 4-OH-BTL-forming activity from racemic BTL was significantly lower than from enantiomeric BTL, indicating a possible metabolic interaction between BTL enantiomers. The in vitro profiles observed in the monkeys were very similar to those in humans, but the stereoselectivity in BTL metabolism [(+)-BTL > (-)-BTL] in the primates was found to be reverse to that in rats [S. Narimatsu et al., Anal. Biochem., 222, 256-261 (1994)]. The 4-OH-BTL-forming activity from BTL enantiomers was significantly suppressed by quinidine and quinine, while the former was more potent than the latter, and also by alpha-naphthoflavone. Furthermore, the activity was also suppressed by antisera against rat cytochromes P450-2D2 and -1A2 in concentration-dependent manners. However, kinetics showed that enantiomeric BTL 4-hydroxylation was monophasic in liver microsomes from marmosets of both genders and from male Japanese monkeys. These results suggest that cytochrome P450-2D and -1A enzymes with similar Km values are involved in BTL 4-hydroxylation in monkey liver microsomes.

Adrenergic beta-Antagonists↗
PubMed1996

Effect of barium in porcelain on bonding strength of titanium-porcelain system.

The bonding strength to titanium, thermal expansion, and bending strength of glassy porcelain containing barium of 5, 10, and 15 mass% were estimated and compared with those of barium-free porcelain, to estimate the effect of barium content on bonding strength to titanium. The three different glassy porcelains containing barium were made by melting at 950 degrees C. The bonding strength of a commercial porcelain to titanium increased with the addition of barium. Bending strength and thermal expansion were not affected by the barium content. Therefore, the addition of barium to porcelain is effective for strengthening the bonding of porcelain to titanium.

Analysis of Variance↗
PubMed1996

Simulation of transient thermal stress in gypsum-bonded investment.

The aim of this study was to clarify the effect of heating rate on the development of both transient and residual stresses in investment molds. Solid, cylindrical, gypsum-based molds were modeled and theoretical calculations made of temperature distributions with a constant heating rate. These calculations used experimental thermal diffusivity data obtained with a laser flash method. The simulations calculated transient thermal stresses during heating and at the end of heating for two surface conditions: an unrestricted surface, and a surface restricted by a casting ring. The simulation model developed nonuniform strains and stresses at casting temperature; tangential stress was compressive at the surface and tensile at the mid-point for the unrestricted surface model. The surface restricted model developed compressive tangential stresses throughout the mold at the casting temperature. This resulted in significant thermal strain differences compared to the magnitudes of expansion of the mold due to heating.

Calcium Sulfate↗
PubMed1996

[Two cases of ossified spinal meningioma].

It is generally known that meningioma has histological pleomorphism and ossification is one of them. In the cases of spinal meningioma, osteoblastic type is rare. We encountered two different types of ossified spinal meningioma. Two cases of ossified spinal meningioma are reported in this paper. One case is that of a 45-year-old male who had a sudden transient tetraparesis with a tumor located in the upper cervical spinal column. The tetraparesis was caused by the patient's head having been hit. Another case is a 74-year-old female, who had progressive paraparesis and hypesthesia in her lower extremities, with a tumor located in the 9th thoracic spinal column. The MRI findings in these cases suggested that an ossified area was included in the tumor. We performed surgical therapy in both cases, and an operative finding was that these tumors had a very hard component. Histopathological diagnosis in both cases was meningioma. The former included isolated matured bone tissue with fat marrow mixed with the tumor tissue, and the latter included scattered matured lamellar bone tissue. These tumors are considered to be osteoblastic in type.

Aged↗
PubMed1995

Estimation of ideal mechanical strength and critical porosity of calcium phosphate cement.

The ideal mechanical strength and critical porosity of calcium phosphate cement (CPC) were estimated to help determine ways to improve its properties. CPC at various porosities was made by packing CPC paste, at various powder-to-liquid (P/L) ratios (2.0-6.0), into a mold under various pressures (0-173 MPa). The mechanical strength of CPC, in terms of diametral tensile strength (DTS), increased with decreases in porosity. Intercrystalline fracture was observed in specimens made without the application of pressure, while fracture within the crystals increased with the packing pressure. These observations support the application of the relationship between DTS and porosity in fractographic equations. The ideal wet DTS and critical porosity of CPC were estimated to be 102 MPa and 63%, respectively. The minimum porosity of the currently used CPC was approximately 26-28%, even when it was packed under 173 MPa, and the maximum DTS value was thus approximately 13-14 MPa. Because reducing the porosity of currently used CPC would be difficult, we conclude that in CPC-related research, we should focus on ways in which to accelerate bone-replacing behavior, in addition to improving the mechanical strength of CPC.

Bone Cements↗
PubMed1995

Non-decay type fast-setting calcium phosphate cement: composite with sodium alginate.

Non-decay type fast-setting calcium phosphate cement (nd-FSCPC) was prepared by introducing sodium alginate (0-2.0 wt%) into the liquid phase of FSCPC. nd-FSCPC was stable even when the cement paste was immersed in distilled water immediately after mixing, whereas conventional FSCPC (c-FSCPC) decayed completely within 1 min upon immersion. The setting time of the cement, approximately 5 min, was not dependent on the presence of sodium alginate. In contrast, the introduction of sodium alginate into conventional CPC, i.e. CPC without neutral phosphate in the liquid phase, resulted in no setting when the amount of sodium alginate introduced was more than 1 wt%. Powder X-ray diffraction analysis revealed no significant difference for the conversion of cement to apatite for any concentrations of sodium alginate studied (0-2.0 wt%). The mechanical strength of the cement increased rapidly with the addition of sodium alginate up to 0.8 wt% when the cement paste was immersed and kept in distilled water at 37 degrees C, whereas further addition of sodium alginate decreased the mechanical strength. The results obtained in this investigation, taken together with sodium alginate's known excellent biocompatibility and absorption behaviour, indicate that the use of sodium alginate composite FSCPC as nd-FSCPC should be of value in orthodontics and oral and maxillofacial surgery where the cement is exposed to blood.

Alginates↗
PubMed1995

In vivo setting behaviour of fast-setting calcium phosphate cement.

The in vivo setting behaviour of fast-setting calcium phosphate cement (FSCPC) between femoral muscles of the rat was investigated to evaluate the possible value of FSCPC for medical and dental application. Conventional CPC (c-CPC) and FSCPC were implanted between femoral muscles, and various aspects of the setting behaviour such as setting time, mechanical strength and conversion ratio of cement into hydroxyapatite (HAP: Ca10(PO4)6(OH)2) were measured by the Vicat needle method, diametral tensile strength (DTS) measurement, and quantitative powder X-ray diffraction (XRD) analysis, respectively. The setting time of FSCPC in vivo was 5-7 min, in contrast to 48 min for c-CPC. As a result of its fast setting, set specimens of FSCPC showed higher mechanical strength from the initial stage than c-CPC. Higher DTS values were observed in FSCPC than c-CPC implanted after 24 h. Powder XRD analysis revealed faster conversion of FSCPC than c-CPC into HAP, which was responsible both for the faster setting and higher mechanical strength from the initial stage. We concluded, therefore, that FSCPC may be used for a wide range of clinical applications, i.e. fields where fast setting is required such as orthopaedic, plastic and reconstructive, and oral and maxillofacial surgery.

Animals↗
PubMed1995

Development of calcium phosphate based functional gradient bioceramics.

A functional gradient bioceramic that can function gradually with respect to body tissue was studied by changing the composition of calcium phosphate gradually from the surface to the inside. Diamond powder was spread on the surface of compact hydroxyapatite (HA) powder and fired at 1280 degrees C under reduced pressure, followed by firing under atmospheric conditions. The sintered body thus prepared was dense and alpha-tricalcium phosphate (alpha-TCP: alpha-Ca3(PO4)2) was found on its surface. The content of alpha-TCP gradually decreased with increasing depth from the surface. In contrast, the content of HA increased with increasing depth from the surface. The gradient ratio of alpha-TCP and HA depends on the firing time for each condition, i.e. reduced or atmospheric pressure. The alpha-TCP formation was ascribed to the decomposition of HA due to the spontaneous combustion of diamond powder.

Biocompatible Materials↗
PubMed1995

Effects of fluoride on the calcium phosphate precipitation method for dentinal tubule occlusion.

Use of the calcium phosphate precipitation (CPP) method makes possible the occlusion of dentinal tubules to approximately 10 to 15 microns from the dentinal surface, and thus shows good potential for the treatment of dentin hypersensitivity. The precipitate formed in the dentinal tubules by the CPP method is, however, not apatite [HAP; Ca10(PO4)6(OH)2], a component of tooth and bone, but dicalcium phosphate dihydrate (DCPD; CaHPO4.2H2O). Since fluoride enhances the conversion of DCPD to HAP, we evaluated the effects of fluoride on the texture of the precipitate formed by the CPP method and on its capacity to occlude dentinal tubules in this in vitro study. CPP solution (1.0 mol/L CaHPO4.2H2O dissolved in 2.0 mol/L H3PO4) was applied to a dentin disk and was subsequently neutralized with a post-treatment solution (1 mol/L NaOH, from 0 to 0.1 mol/L NaF). Scanning electron microscopy revealed that the precipitate occluded dentinal tubules to a depth of approximately 10 to 15 microns from the dentinal surface, regardless of the NaF concentration (from 0 to 0.1 mol/L) in the post-treatment solution. Also, dentin permeability was reduced to 15% by the CPP treatment regardless of the NaF concentration. The Ca/P molar ratio of the precipitate, measured by x-ray micro-analysis, was higher (1.25 +/- 0.04) in the presence of NaF than in its absence (1.03 +/- 0.01). For further identification of the precipitate formed in the dentinal tubules, the same procedure was used in glass tubes (diameter, 1 mm), so that a larger amount of precipitate would be obtained.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium Phosphates↗
PubMed1995

Duration of dentinal tubule occlusion formed by calcium phosphate precipitation method: in vitro evaluation using synthetic saliva.

The use of a calcium phosphate precipitation method occluded dentin tubules with apatitic mineral and, thus, showed good potential for the treatment of dentin hypersensitivity. The aim of this study was to elucidate the occluding behavior of the precipitate in the oral environment. Dentin disks treated by the calcium phosphate precipitation method, and disks treated with potassium oxalate, NaF, and SrCl2 solutions, were immersed in synthetic saliva, which was regularly replenished so that ionic concentration would be maintained. Treatment of dentin disks by the calcium phosphate precipitation method immediately reduced dentin permeability to 6 +/- 8%. When the disk was immersed in synthetic saliva, dentin permeability remained low, even seven days after immersion. Scanning electron microscopic observation showed no distinct boundary line between the precipitate and intertubular dentin; this indicated further mineralization on the precipitate. Potassium oxalate treatment also reduced the dentin permeability to 8 +/- 3%. However, the dentin permeability gradually but steadily increased with immersion time, reaching 39 +/- 14% at seven days. To elucidate the mechanism underlying dentin permeability changes in synthetic saliva, we immersed the precipitates, i.e., apatitic mineral and calcium oxalate, in a fixed volume of synthetic saliva. When calcium oxalate was immersed in synthetic saliva, there was a large concentration of oxalate ions, indicating dissolution of the calcium oxalate; this phenomenon was ascribed to the increase in dentin permeability. In contrast, calcium and phosphate ions decreased when apatitic powder, the precipitate formed by the calcium phosphate precipitation method, was immersed in synthetic salvia. The decrease in the calcium and phosphate ions in synthetic saliva indicated further precipitation of calcium phosphate on the apatitc precipitate.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Influence of crystallization on strength and color of castable glass-ceramics containing two crystals.

The mechanical properties, color and transparency of glass-ceramics are highly dependent on the ceramming temperature and/or amount of the crystal phase in the glass matrix. In this study, the influence of crystallization on the strength and color, translucency of castable ceramics containing crystalline apatite and magnesium titanate were measured. It was concluded that magnesium titanate precipitated during ceramming, appeared to be an important factor in decreasing total transmittance and in determination of the color of glass-ceramics.

Apatites↗