Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Prosthodontic Society  

<b>Purpose: </b>Little is known about the corrosion caused by contact with Ag-Pd-Cu-12Au alloys which are commonly used for cast crowns. The purpose of this study was to investigate the state of early corrosion behavior by contact with Au-Pd-Cu-Au alloys containing different amounts of Cu using X-ray photoelectron spectroscopy.<br><b>Materials and Methods:</b> Three kinds of plate specimens of Ag-Pd-Cu-Au alloy containing different amounts of Cu were cast, and two specimens each were fixed and immersed into corrosion liquid for eight weeks. Then, the specimens were ultrasonically cleaned with acetone and ultra pure water and the corroded surface was analyzed using X-ray photoelectron spectroscopy. The depth that could be analyzed by XPS was about 10 nm, so the analytical results, it was the outermost surface and internal within 10 nm.<br><b>Results:</b> Remarkable discoloration was observed on the edge of the contacted area on the specimen containing a larger amount of Cu. As early corrosion products, Ag₂O, PdO, CuO, Cu₂S and CuSO₄ were observed and PdO was detected in the deeper part in many specimens with larger content of Cu. There was a higher ratio of CuSO₄ in the specimen with a large content of Cu, and the ratio of CuO and Cu₂S increased in the deeper part. The presence of Cu₂S was detected from the surface to the inside of the specimen with a smaller content of Cu.<br><b>Conclusions:</b> In the case of contact with Ag-Pd-Cu-Au alloys with different Cu amounts, Ag₂O, PdO, CuO, Cu₂S and CuSO₄ were formed in early corrosion.

DOI： 10.2186/ajps.7.371

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Language：Japanese   Publishing type：Research paper (international conference proceedings)   Publisher：Wiley  

DOI： 10.1111/joor.12254

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Other Link： http://id.nii.ac.jp/1681/00000296/

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER IRELAND LTD  

Purpose: The purpose of this study was to evaluate the distribution of bubbles, degree of mixing, flowability and mechanical strength of powder-liquid reline material by manually and with a rotation-revolution (planetary) mixer, and to determine the usefulness of a rotation-revolution mixer for this application.Methods: Powder-liquid reline material (Mild Rebaron, GC, Tokyo, Japan) was mixed with a powder to liquid ratio of 1:0.62 according to the manufacturer's instruction. Two methods were used to mix it: mixed by manually ("manual-mixing") and automatically with a rotation-revolution mixer (Super Rakuneru Fine, GC, Tokyo, Japan; "automatic-mixing"). Disc-shaped specimens, 30 mm in diameter and 1.0 mm in thickness, were used to observe the distribution of bubbles in at 10x magnifications. Flowability tests were carried out according to the JIS T6521 for denture base hard reline materials. A three point bending test was carried out by a universal testing machine. Elastic modulus and flexural stress at the proportional limit were calculated.Results: A median of 4 bubbles and inhomogeneous were observed in manual-mixed specimens. However, no bubbles and homogeneous were observed in automatic-mixed specimens. Flowability was within the JIS range in all mixing conditions and did not differ significantly across conditions. The elastic modulus was the same for manual-mixed and automatic-mixed specimens. On the other hand, the flexural stress at the proportional limit differed significantly between manual-mixed and automatic-mixed specimens.Conclusion: The results confirm that rotation-revolution mixer is useful for mixing powder-liquid reline material. Automatic-mixing may be recommended for clinical practice. (C) 2014 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved.

DOI： 10.1016/j.jpor.2014.11.002

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We report experimental results about the effect of polarity of electrode and anodized titanium oxide film on the deposited materials by electrolysis of an acidic calcium phosphate solution. Mirror-polished titanium and anodized titanium were Used as anode or cathode, and a Pt plate was used as a counter electrode. The load voltage was held constant at 20 VD C. No deposited materials were found on the anode surface. On the other hand, dicalcium phosphate dihydrate (DCPD) was deposited on the cathode surface at the beginning of the electrolysis. After the electrolysis time 600 s, the non-stoichiometric hydroxyapatite (HAp) with several hundred nanometers was formed on the specimen surface. Based on X-ray photoelectron spectroscopy data, the anodized oxide film contained both P5+ and P3+ ions. This characteristic of the oxide film and the electrolysis conditions were related to the behavior of the deposition of ultra fine HAp with high crystallinity.

DOI： 10.4012/dmj.2012-197

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Microcapsules containing active drugs, e.g. an antimicrobial agent, with a hydroxyapatite (HAp) shell are expected to prevent infection and to improve osseointegration Simultaneously when used as implant materials. This study was conducted to investigate the effects of etching with hydrofluoric acid (HF) to change the surface morphology of titanium in cases of adhesion of calcium-deficient HAp microspheres onto titanium. The microspheres were mixed with Hanks' balanced salt solution (HBSS) to prepare slurry; the slurry was then put between two titanium disks that had been etched and kept soaking in HBSS for seven days at 310 K. The coverage and the degree of adherence of the microsphere were evaluated using electron probe microanalysis. The etching at an HF concentration of 0.10 mol/L caused the greatest adhesion. Changing the temperature between 303 and 323 K showed a tendency for the degree of adherence to increase.

DOI： 10.4012/dmj.28.700

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Electrochemical deposition of calcium phosphate (CAP) on valve metals such as Ta, Nb, and Zr, was performed by anodic oxidation with alternate polarity inversion at an applied 20 VDC. A saturated hydroxyapatite(HAP)-phosphoric acid solution (pH 3) was used as the electrolyte. MR, XRD, and XPS were employed to investigate the detailed characteristics of the deposition. HAP was precipitated on Ta; HAP including brushite and monetite on Nb; and HAP and monetite on Zr. The Ca/P atomic ratios were 1.3-1.5 by XPS, and HPO42- bands were detected on Ta by FTIR. Therefore, the HAP precipitated on Ta was a Ca-deficient HAP. In addition, the XPS spectra of the specimens showed that phosphate ions were incorporated into the anodic oxide film. Deposits with nano-grain size were observed by AFM. The results confirmed that CAP with nano-grain size was deposited on valve metals by the anodic oxidation with polarity inversion.

DOI： 10.4012/dmj.28.513

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Nitrides used in this experiment are h-BN, AIN and Si_3N_4. The feasibility of using the nitrides was studied as wax pattern coating materials for a Co-Cr alloy in an atmosphere of argon. Wax patterns were painted with the nitride coating material (first investing), and then it was outer-invested witla a mixture of gypsum-bonded investment and water (second investing). The temperature of mold was 700℃, and the thin specimens were cast with an argon arc vacuum-pressure casting machine in the Co-Cr alloy (composition Co : 63 wt%, Cr : 27, Mo : 5, Bat. : 5 ; melting point : 1,380℃). Surfaces of cast specimens were investigated with the unaided eye, a scanning electron microscope, a surface roughness analyzer, an X-ray diifractometer and a micro-Vickers hardness tester. Furthermore, the cast clasp using an h-BN coating material were made and investigated with the unaided eye. Results were sumcmarized as follows : 1. The nitrides inhibited remarkably a reactiona between the cast specimen and the investment. 2. BN had the good effect of separation. 3. The cast surface coated BN had less clitaging than uncoated one. This indicated that cleansability and work efficiency were improved. 4. The surface roughness (Rz) of the specimens decreased to 32, 42 and 60% of the control with BN, Si_3N_4 and AlN, respectively. 5. A hardness change of the alloy by casting was the least in the case of using BN. 6. BN also had the effect in fabricating a cast clasp in the clinical form.

DOI： 10.2186/jjps.34.1235

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The present study examined the feasibility of hexagonal boron nitride (hBN) as a wax pattern coating material for gold alloy casting in air. After wax patterns were coated with hBN, they were outer-invested with a gypsum-bonded investment. The thin specimens made of the gold alloy, 0.55 mm in thickness, were cast in air. The color of the cast surface by using hBN was rusty red. The X-ray diffractometer analysis revealed that copper oxide produced on the hBN cast surface was the only Cu_2O, and CuO produced on the control was not detected. This means that hBN remarkably inhibited the oxidation during casting. Thus, the use of hBN could be effective in hardness of the cast surface.

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The aim of this study was to characterize the adhesion of mineral particles to a metal (titanium) plate by electrolysis. MMA including a conductive monomer and zircon powder treated with stearic acid was used as an electrolyte. Titanium and carbon plates were used as electrodes. Twenty volts DC were applied between the electrodes for 3,600 s. EPMA revealed the adhesion of zircon particles to the metal surface. In addition, S, O elements were concurrently detected on and around the particles. Since both elements were derived from the conductive monomer, the present study indicated the formation of an organic material including conductive monomer on the metal surface preceded the adhesion of zircon particles.

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The water-powder ratio (W/P ratio) affects compressive strength of dental stone. In this study, we investigated the effects of water droplets adhering on a mechanical spatulator with vacuum and hand spatula on W/P ratio. The amount of water droplets was measured using an electronic balance. The compressive strength of dental stone was calculated based on the loaded weight. The total amount of water droplets adhering onto spatulator (volume; 250 and 500 mL) and a hand spatula were 0.90 mL (SD 0.10) and 1.33 mL (SD 0.12), respectively. The compressive strength of the dental stone were 10.23 kg/mm^2 (SD 0.27) and 6.89 kg/mm^2 (SD 1.31) at W/P ratio 0.20 and 0.23, respectively. Thus, the total amount of water droplets adhering on those instruments should be taken into consideration when mixing dental stone.

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The aim of this study was to investigate the effect on corrosion products due to difference in Cu content. We prepared three kinds of Ag-Pd-Cu-Au alloys with difference Cu content. After casting in 10 × 20 × 1 mm^3, the contacted casting plates were immersed in corrosion solution for 8 weeks at 37℃. After immersed, we analyzed alloy surface by XPS. In spite of Cu content, a peak derived from PdO was confirmed in Pd3d XPS spectra of all specimens.

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Japanese society for dental materials and devices has title system of Dental Materials Adviser (DMA) and Dental Materials Senior Adviser (DMSA), which are titles about dental materials and devices. Dentists use dental materials and devices in their clinics. Therefore, it appears to be beneficial for patients that dentists take DMA and DMSA. In this study, we explored the strategy beneficial for patients by utilizing this title system. Since Japan dental association (JDA) is the largest association of dentists including general practitioners, we will be able to inform dentists of our title system by using the advertising media in the JDA. If the JDA agreed with our plan, the number of DMA and DMSA would increase dramatically. Consequently, our strategy would result in the benefit for thousands of patients.

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The aim of this study was to prepare organo-mineral complex by electrolysis and to characterize it. MMA including conductive monomer and oxide with a stearic acid treatment was used as an electrolyte. Titanium and stainless substrate were used as electrodes. Twenty volts DC were applied between the electrode and Pt counter electrode in the electrolyte for 3,600 s. FTIR results confirmed the preparation material to be a PMMA. Mineral particles were well dispersed on the PMMA matrix according to the EPMA results. The mineral particle size was the order of submicron by AFM image. Consequently, the organo-mineral complex was easily prepared by the electrolysis.

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Mechanical properties of powder-liquid type lining materials are inferior to those of heat cured denture base resins, which causes the reduction of the strength of the denture. We studied the effect of rotation-revolution mixer compared with hand mixing for powder-liquid type denture lining material on mechanical properties. Flexural stress at the proportional limit was significantly increased, while flexural modulus was similar to the specimen made with rotation-revolution mixer mixing.

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Self-curing acrylic resin is used in a variety of clinical applications, e.g. fabricating provisional restorations, adjusting occlusion, and repairing dentures. However, this resin is inferior to heat-curing acrylic resin in chemical and mechanical properties. In this study, to improve these properties, we irradiated low-energy electron beam (LEB) to polymer particles, and then the polymer particles were polymerized by ordinary method. We investigated the influence of LEB irradiation on polymer particles. Consequently, LEB irradiation caused formation of the free radical, which contributed to increase of flexural strength.

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The aim of this study was to investigate the characterization of calcium phosphate deposited on magnesium and its alloys (AZ31 and AZ61) by applying polarity inversion electrolysis. Magnesium and its alloys were used as electrodes. One volt DC was applied between the electrode and Pt counter electrode in an acid calcium phosphate solution for 600s. The polarity was swapped every 60s. XRD results confirmed the deposited material to be a magnesium hydroxide and brushite. XPS spectrum of Mg2p was observed for the outermost surface. Therefore, the brushite was deposited locally on the metal surface.

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Appropriate flow property of composite resin is required for application to a variety of prepared cavities. Three types of commercial composite resin having different flow properties were investigated with electron probe micro-analyser (EPMA), infrared spectroscopy (FT-IR) and atomic force microscope (SPM). The filler-size of the most flowable type was larger than those of other two types. The weight content of filler was almost equal among these three types. In conclusion, the filler size plays an important role for flow properties.

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The postgraduate education on dental materials and devices is very important to improve the quality of the dental treatment. In the study, effectiveness of workshop (WS) as the system in the postgraduate education on dental materials and devices was investigated based on the questionnaire survey. Most of the participants replied "I got something great from what WS provides.", "WS is effective in the postgraduate education." and "I want to participate again." In conclusion, WS is effective as the system in the postgraduate education on dental materials and devices.

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Ag-Pd-Cu-Au alloys are widely used as dental casting alloys. However, they have some clinical problems such as corrosion and discoloration. XPS is effective for analyzing the uppermost surface of dental alloys. In this study, we used XPS to investigate surface chemical properties at none-discoloration areas of removed Ag-Pd-Cu-Au alloys. According to the results, in addition to the alloy elements, S, C, N and O were detected at areas of none-discoloration. Therefore, the formation of oxides and sulfides was estimated even at areas of none-discoloration.

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The influence of fluoride ions on the corrosion behavior of Ag-based alloy was investigated. The cast specimens of a commercial Ag-based alloy (65Ag-22Sn-13Zn) were immersed in 7% polyvinylpyrrolidone iodine (povidone-iodine) solution with and without fluoride ions. After that, the alloy surface was examined by means of XPS to investigate the corrosion behavior. In the case of solution containing fluoride ions, notable intense Sn and F peaks were detected, suggesting that tin fluoride compound was formed.

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The aim of this study is to investigate the effect of anodic oxide film thickness on characteristics of deposited calcium phosphate by applying polarity inversion electrolysis method. After mirror polished titanium were treated with anodic oxidation at 20 and 50VDCs for 60s, they were used for the negative electrode. Finally, calcium phosphate solution was electrolyzed at 20VDC for 600s. XRD and AFM were employed to study the characterization of the deposited calcium phosphate. A thick oxide film formed by the anodic oxidation reduced the electrolytic current in the electrolysis. The smaller current caused the smaller deposited calcium phosphate particles.

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PMMA (Poly methylmethacrylate) is used widely as denture base materials. To improve mechanical properties of polymers, the surface modification of PMMA by electron beam irradiation has been studied. In this study, low-energy electron beam (LEB) was irradiated on PMMA surface. We investigated the surface properties before and after LEB irradiation. According to our results, it is demonstrated that LEB irradiation causes main chain scission, increase of the surface roughness, and improvement of the wettability.

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Denture reline materials are liable to involve bubbles during hand mixing. Moreover, it is difficult to make them homogeneous. In this study, for mixing denture reline materials, we used the rotation-revolution mixer that was popular as automatic alginate mixer. Compared the mixer with the hand mixing, the mixer made the polymer and monomer mixture more homogeneous without any bubbles. These results suggest that the mixer was effective for decreasing bubbles and for making the homogeneous mixture of denture reline materials.

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Other Link： http://search.jamas.or.jp/link/ui/2011150484

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The aim of this study is to investigate the effect of the coatings on the deposited calcium phosphate. The organic coatings was formed on titanium by electrolyzing MMA, including conducting monomer at 150 VDC for 3,600 s. Calcium phosphate was deposited on the treated specimen by the polarity inversion method in calcium phosphate solution (pH 3) at 20 VDC. XRD, FTIR and AFM were employed to study the characterization of calcium phosphate. The deposited calcium phosphates are influenced by an electrical characteristic of the organic coatings.

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PMMA widely used as denture base, is degraded under various environments. The surface properties of the PMMA are well characterized by the X-ray photoelectron spectrometer. However, this technique is restricted because of damage caused by the measurement process, such as X-ray or Ar ion irradiation. It was recognized that Ar ion irradiation, used for surface cleaning, and the long period of Al Kα irradiation give serious damage to the structure of the PMMA surface.

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The aim of this study is to investigate calcium phosphate (CAP) deposition on organic thin film coated titanium. The organic thin film was coated on titanium by electrolyzing MMA including DMSO and a conducting monomer at 110 and 150 VDC for 3,600s. CAP deposited on the treated specimen by polarity inversion method in a hydroxyapatite (HAp) saturated solution (pH 3). XRD, FTIR and AFM were employed to study the characterization of deposited CAP. The deposited CAP was Ca-deficient HAp and brushite for 110 VDC. For 150 VDC, these CAPs and calcium hydroxide were detected. Hybrid coatings of organic thin film/CAPs codeposited on titanium was formed by the electrolyzing method.

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The water-powder ratio for gypsum-bonded investment influences the setting expansion. In this study, the effect of shaking off water drops on mechanical spatulator and hand spatula were investigated. The amount of water drops was measured by using an electronic balance. The total amount of water drops on the mixing set decreased very much after two times shaking off. By two times shaking off water drops, the influence on the setting expansion ratio of water drops can be avoided at the worst condition. The results demonstrated that shaking off water drops was effective for the setting expansion of gypsum-bonded investment.

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The final purpose of this study is to develop a high-performance implant, which can prevent infection for a couple of day immediately after the operation and then promote the osseointegration. As a fundamental study, hollow calcium-deficient hydroxyapatite microspheres revealing high solubility were made to adhere onto a titanium screw, of which the surface had been treated with hydrofluoric acid. The effects of conditions for the surface treatment on the surface morphology of titanium and the adhering amount of the microspheres were investigated.

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The water-powder ratio (W/P) for stone or gypsum-bonded investment influences setting expansion. In this study, the effects of water drops adhered to mechanical spatulator and hand spatula on W/P were investigated. The amount of water drops was measured by using an electronic balance. The setting expansion rates of an investment were also measured. The total amount of water drops adhered to 250 and 500 ml spatulator and hand spatula were 0.90 ml (SD 0.09 ml) and 1.31 (SD 0.12), respectively. The setting expansion rates of the investment were 0.60 % (SD 0.04 %) and 0.47 (SD 0.04) at W/P 0.31 and 0.35, respectively. The results demonstrated that the total amount of water drops sometimes influences W/P.

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The purpose of this study is to study the dissolution behavior of dental Ag-Pd-Cu-Au alloys in artificial saliva including protein. The cast specimens (surface area of 6 cm^2) were polished using #1,000 SiC waterproof paper. Fusayama's artificial saliva, Hank's balanced salts solution, and artificial saliva Saliveht with or without mucin as immersion solutions for metal extraction were prepared. The cast specimen was immersed in 50 mL of each immersion solution, and incubated at 37℃ for 7 days. ICP-MS worked by analyzing the released elements. The level of Cu, Zn and Ag from the tested alloys in the Fusayama's artificial saliva without mucin was about twice as high as that of elements in the saliva with mucin.

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The aim of this study is to investigate an organic film formed on titanium surface by electrolysis of ionic liquid. The ionic liquid of imidazole system, [C_8H_<15>N_2][PF_6], was used for electrolyte preparation. Mirror polished titanium and platinum plate as an electrode were used. A constant VDC of 40 was applied between the electrodes for 180 s via a DC power unit. FTIR and AFM were employed to study the organic film. The electrolytic oxidation reaction of the imidazole ring resulted in forming the organic film.

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To investigate the relationship between the surface texture of Ti implant and the adsorption behavior of biomolecules, two kinds of implants (having polished surface or grooved surface) were fabricated from commercial pure titanium. They were inserted to rat bone, retrieved after either 3 hours or 7 days, and analyzed with X-ray photoelectron spectroscopy. Although the amounts of proteins adsorbing were almost equal on the both surfaces, the amount of proteoglycan adsorbing on the polished surface was about 2 times larger than that on the grooved surface.

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Recently, the number of accidents, involving dental bur break has increased in our hospital. It has been thought that one of the causes of the accident might be the deterioration of dental burs by the repeated washing and sterilizing. Purpose : This study aims to clarify the cause of the deterioration of dental burs in the process of washing or sterilizing. Materials and methods : The burs examined were the Zekrya burs made of tungsten carbide. The burs were washed by ultrasonic cleaner or by washer-disinfector, or sterilized by autoclave or by the HPDS (Hydrogen peroxide/Plasma Discharging Sterilization at low temperature). After repeating the washing or sterilizing process 30 times, the surface of each bur was observed by the EPMA (Electron Probe Micro-Analyzer) by 7,000-time magnification. Results: 1. The EPMA analysis showed that the surfaces of the blade of the dental burs treated by the HPDS contained many cracks. 2. The surfaces of the blade of the dental burs that were treated by the autoclave showed a porous aspect. 3. Ultrasonic cleaner and washerdisinfector did not influence the surfaces of the blade of the dental burs. 4. At macroscopic level, the level of the surface deterioration may be distinguished by the darkening tendency of the bur's color.

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DOI： 10.14832/gsjsdmd.2005f.0.52.0

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Language：Japanese   Publisher：明倫短期大学  

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Electrochemical buffing, a combined process of electrochemical and mechanical polishing, was applied to titanium casting. Mixture of alpha-Al2O3 suspension (average grain diameter of 5 mu m) and 5% KNO3 solution was used as abrasive slurry. Specimen and experimental wheel buff were respectively connected to the positive and negative poles of a DC source, whose potential ratings ranged from 0 V (MEP) to 10 V (ECB10). Surface roughness, hardness, color, and cleanness were investigated. ECB10 surface produced a gold color and attained a mirror finish, as its roughness value was only one-quarter that of MEP. High amount of aluminum was present in MEP surface. Its bond state entirely differed from that of alpha-Al2O3, hence indicating surface alteration due to chemical reactions with the abrasive material. At higher potentials, reaction products might be dissolved anodically, so that the surface was chemically clean to some extent. The surface also became rich in OH-.

DOI： 10.4012/dmj.23.504

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Electrochemical buffing, a combined process of electrochemical and mechanical polishing, was applied to titanium casting. Mixture of alpha-Al2O3 suspension (average grain diameter of 5 microm) and 5% KNO3 solution was used as abrasive slurry. Specimen and experimental wheel buff were respectively connected to the positive and negative poles of a DC source, whose potential ratings ranged from 0 V (MEP) to 10 V (ECB10). Surface roughness, hardness, color, and cleanness were investigated. ECB10 surface produced a gold color and attained a mirror finish, as its roughness value was only one-quarter that of MEP. High amount of aluminum was present in MEP surface. Its bond state entirely differed from that of alpha-Al2O3, hence indicating surface alteration due to chemical reactions with the abrasive material. At higher potentials, reaction products might be dissolved anodically, so that the surface was chemically clean to some extent. The surface also became rich in OH-.

DOI： 10.4012/dmj.23.504

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DOI： 10.14832/gsjsdmd.2004f.0.54.0

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Language：Japanese   Publisher：The Japanese Society for Dental Materials and Devices  

In a two-chamber pressure-casting system, the rate of casting pressure increase depends on the exhausting rate of argon gas in the mold. The purpose of this study was to measure the pressure change in a mold cavity after the start of casting and to investigate the influence of mold temperature and thickness on the initial rate and later value of casting pressure. Moreover, a new casting mold with an experimentally improved crucible was proposed and its influence on the casting pressure was also investigated. Regardless of crucible condition, the initial rate of casting pressure decreased with mold temperature and thickness. Although the difference in crucible condition did not significantly influence the initial rate, the improved crucible increased the later value of casting pressure.

DOI： 10.18939/jjdm.23.1_1

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Language：Japanese   Publisher：日本医療機器学会  

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Synthesis method of fine and pure AlN powder from Al powder by means of floating-type fluidized-bed was investigated. Concentration of oxygen and water vapor in reacting nitrogen was carefully controlled in. the range 4 to 600 ppm. Ultrapure Al powder as a raw material was continuously fed into nitrogen stream with a flow rate of 1.6 cm/s from the end of the reactor, and was nitrided, at 1550 degreesC. AN powders which were nitrided in nitrogen containing oxygen and/or water vapor in the range 50 to 100 ppm, were considered to be suitable for fabrication of high thermal conductive ceramics, because the resulting AN powders were perfectly nitrided and the color of them was pure white indicating the powders being ultrapure. The amounts of impurities such as metals and oxygen context in the powders were extremely low. The powders were composed of primary particles with 0.1 to 0.2 mm in size and specific surface areas of them were 10.0 m(2)/g. The formation process of the fine AlN powder was presumed to be constituted of several elementary reaction steps involving explosive and combustive nitridation of Al particles. The AN powder had good sinterability, and high thermal conductive AlN ceramics with value of 255 W/mK could be obtained by sintering at 1900 degreesC for 32 hours in a nitrogen with aid of 3wt% to 5 wt% Y2O3. Neither pore nor precipitation of the second phase was observed at the gram boundary, and then the extensive gram growth was observed.

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DOI： 10.14832/gsjsdmd.2003f.0.79.0

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Language：Japanese   Publisher：The Japanese Society for Dental Materials and Devices  

Since the mold cavity is exposed to the melting chamber in a two-chamber casting unit, the cavity is filled with Ar gas till casting of molten titanium. Thus, the gas evacuation rate immediately after melt casting must influence the castability and generation of internal defects. In this study, the cavity pressure was measured using a mold simulating a two-chamber casting process at room temperature and the results were converted into the casting pressure. Mold permeability and preset pressures in the melting and casting chambers were considered as factors influencing the quality of casting. The higher the mold permeability and the higher the difference between the preset pressures, the higher level the casting pressure rapidly reached. The results suggested that the choice of investment material should be made from the perspective of mold permeability suitable to the casting mechanism.

DOI： 10.18939/jjdm.22.1_37

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DOI： 10.14832/gsjsdmd.40.0.89.0

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Language：Japanese   Publisher：Japan Prosthodontic Society  

Purpose: To help frame long-range programs for education, research, and clinics on bridges and dentures, we estimated the numbers of these prosthetic appliances that will be needed in the future.<BR>Methods: People of age 65 and above, including dependent elderly, were investigated. The average numbers of these appliances per person were estimated by regression analysis based on survey reports of dental diseases. Several regression lines were corrected so that mutual intersections would not occur between age groups and the estimated value would not exceed each upper limit. The total numbers of these appliances in the future were calculated from the estimated average numbers and population projections.<BR>Results: It was projected that the numbers of bridges and dentures used by the elderly would increase 2.0 times (2.2-1.1 times, by 95% confidence interval) and 1.5 times (1.8-1.0 times) in 20 years, respectively, and plateau during the subsequent 10 years. The older the age group was, the higher these rates of increase would become. The numbers of bridges and dentures for dependent elderly people were also estimated to increase 2.7 times (3.2-1.0 times) and 1.8 times (2.2-1.0 times) in 25 years, respectively.<BR>Conclusions: We will be faced with the importance of dental education, research, and clinics on bridges and dentures for the elderly and dependent elderly people.

DOI： 10.2186/jjps.45.227

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Language：Japanese   Publisher：Niigata University  

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Language：Japanese   Publisher：The Japanese Society for Dental Materials and Devices (JSDMD)  

This study evaluated the pressure behavior of both the casting chamber and the cavity in the mold using an enclosed one-chamber casting unit. An experimental device with a pressure sensor modeled on the casting system was attached to the casting unit. The chamber pressure rose rapidly and reached half of the preset casting pressure within 0.2s after introducing argon gas into the chamber. Both the preset casting pressure and the gas permeability in the mold strongly influenced the differential pressure between the chamber and the cavity. When a mold with a high level of rising pressure in the cavity, i.e.a mold with higher gas permeability, was used, a large quantity of argon gas penetrated the cavity through the mold wall before the cavity was filled by the molten metal. For this reason, it was thought that some casting defects, such as incomplete casting or gas inclusion, often occur. This study showed that it is desirable to use a mold with lower gas permeability in an enclosed one-chamber casting unit.

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Although titanium has been widely used in prosthetic appliances, such as cast removable partial denture frameworks, high quality castings are still difficult to obtain. This study proposes a new partition technique using a metal foil for improving castability of a two-chamber pressure casting unit. The metal foil was formed beforehand to bring it in contact with the mold rucible wall so that no clearance was left behind it. Using this formed foil, the mold cavity can be completely isolated from the upper chamber and can be maintained in a vacuum even after the rupture of the foil. Accordingly, a large casting force is generated very quickly, and as a result, castability is expected to be significantly improved. This expectation was confirmed by the experiments using wax patterns including thin plate and mesh plate.

DOI： 10.4012/dmj.19.307

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Language：English   Publisher：Japanese Society for Dental Materials and Devices  

Although titanium has been widely used in prosthetic appliances, such as cast removable partial denture frameworks, high quality castings are still difficult to obtain. This study proposes a new partition technique using a metal foil for improving castability of a two-chamber pressure casting unit. The metal foil was formed beforehand to bring it in contact with the mold rucible wall so that no clearance was left behind it. Using this formed foil, the mold cavity can be completely isolated from the upper chamber and can be maintained in a vacuum even after the rupture of the foil. Accordingly, a large casting force is generated very quickly, and as a result, castability is expected to be significantly improved. This expectation was confirmed by the experiments using wax patterns including thin plate and mesh plate.

DOI： 10.4012/dmj.19.307

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A non-phosphate bonded investment including quartz capsuled with stabilized zirconia was developed for casting titanium. The mechanical properties of castings were compared between the experimental investment and a commercially available phosphate-bonded silica investment. The tensile strength values were almost the same for both castings, while the elongation was higher than that of castings from the commercial investment. Although the inner hardness was almost the same for both castings, the hardness in the surface layer was lower. The reaction layer of the casting was clearly thinner. These results suggested that the capsulizing zirconia significantly reduced the reaction of molten titanium with silica, which improved the quality of titanium casting.

DOI： 10.18939/jjdm.18.4_287

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Language：Japanese   Publisher：Japan Prosthodontic Society  

Double casting method (cast on technique) is sometimes used for attachment work. As to this method, the present study was conducted to investigate the partial deformation of casting and the castability of the second casting. A wax sheet stuck on the first cast plate of a gold alloy was invested with a gypsum-bonded investment. Using a centrifugal casting machine, two kinds of alloy were cast in the mold heated to 700°C: one was the same alloy as the first casting and the other was a silver-palladium-gold alloy.<BR>Protuberances on the first casting and the corresponding concaves on the second casting were found approximately beneath the sprue. Some protuberances appeared to be wavy, while the others appeared to be hemispherical, with a maximum height of 220μm. There were no differences in the size and shape of crystal grain as well as the composition between the protuberance and the body of the first casting. Therefore, the protuberances did not result from the adhesion of the molten metal to the first casting, but from the partial deformation of the first casting. In case of using a silver-palladium-gold alloy for the second casting, some of the first castings had concavities.<BR>The castability of the second casting was significantly low, compared with general casting.

DOI： 10.2186/jjps.42.271

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Other Link： http://search.jamas.or.jp/link/ui/1998203960

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Bite force measurement on intercuspal clenching in normal subjects using the pressure sensitive sheet "Dental Prescale" showed that larger bite forces were applied to the posterior teeth than to the anterior teeth. In this study, an experimental model revealed that the even thickness of the pressure sensitive sheet was one of the influential factors in this characteristic distribution.<BR>The experimental model consisted of 14 steel ball-bearings, used as substitutes for the dentition, and a glass slab which were respectively mounted in the maxillary and mandibular elements of a semiadjustable articulator. Three kinds of loading conditions were determined and applied to the upper member with an Instron-type testing machine; then contact forces were compared with the Occluzer FPD-703. Firstly, the upper member was removed from the articulator and the pressure sensitive sheet was loaded directly. Secondly, the condylar elements of the articulator were locked through centric latches, and thirdly, the condylar elements were not locked.<BR>The direct load distributed contact forces almost equally to each steel ball. On the contrary, the load with locked condylar balls distributed larger contact forces to the posterior steel ball-bearings than to the anterior ones. However, the unlocked load showed a similar distribution to the direct load.

DOI： 10.2186/jjps.41.710

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The possibility of the segregation under solidification process using a centrifugal casting machine was investigated using an electron probe microanalyzer with elemental distribution map, line analysis and quantitative analysis. When a very small quantity of platinum was added to local molten titanium during the casting process, macroscopic segregation was observed under conditions of density difference of 0.1g/cm3 at the most, confirming that the centrifugal force of the casting machine is extremely strong. When a Ti -6Al-4V alloy was cast, however, no macroscopic segregation was observed. The centrifugal force of the casting machine examined in the present study hardly results in the body-force segregation in this titanium alloy.

DOI： 10.4012/dmj.15.212

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DOI： 10.18939/jjdm.15.2_137

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DOI： 10.18939/jjdm.15.6_532

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The possibility of the segregation under solidification process using a centrifugal casting machine was investigated using an electron probe microanalyzer with elemental distribution map, line analysis and quantitative analysis. When a very small quantity of platinum was added to local molten titanium during the casting process, macroscopic segregation was observed under conditions of density difference of 0.1g/cm3 at the most, confirming that the centrifugal force of the casting machine is extremely strong. When a Ti -6Al-4V alloy was cast, however, no macroscopic segregation was observed. The centrifugal force of the casting machine examined in the present study hardly results in the body-force segregation in this titanium alloy.

DOI： 10.4012/dmj.15.212

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This study investigated the contamination of abraded Ti surfaces. Using a polishing machine, specimens were abraded with waterproof SiC grit papers under water cooling. The abraded surfaces were examined using element analysis, X-ray diffraction, and hardness tests. Contaminant deposits with dimensions reaching about 30 μm were observed throughout the surface. In these deposits, Ti was apparently reduced by about 10% and replaced by Si and O. The chemical bond state of the Si was similar to that of SiC or a titanium suicide. The O was solute in Ti, which increased the surface hardness. The contaminant deposits were amorphous or very thin. The contamination of Ti, the extent of which was related to hardness, resulted from a reaction with abrasives.

DOI： 10.4012/dmj.15.11

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This study investigated the contamination of abraded Ti surfaces. Using a polishing machine, specimens were abraded with waterproof SiC grit papers under water cooling. The abraded surfaces were examined using element analysis, X-ray diffraction, and hardness tests. Contaminant deposits with dimensions reaching about 30 μm were observed throughout the surface. In these deposits, Ti was apparently reduced by about 10% and replaced by Si and O. The chemical bond state of the Si was similar to that of SiC or a titanium suicide. The O was solute in Ti, which increased the surface hardness. The contaminant deposits were amorphous or very thin. The contamination of Ti, the extent of which was related to hardness, resulted from a reaction with abrasives.

DOI： 10.4012/dmj.15.11

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Language：Japanese   Publisher：新潟歯学会  

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Language：Japanese   Publisher：The Japanese Society for Dental Materials and Devices (JSDMD)  

Casting defects and titanium flow using a one-chamber pressure casting machine were observed by the transparent X-ray method and molten tracer element method, respectively.To clarify the relation between casting defects and filling types, three types of wax patterns were invested at one time.To estimate the influence of mold permaebility, three types of investment which significantly differed in permeability were used.As a result, investments with high permeability cause many internal defects in thick plate castings and external defects on thin plate castings and mesh castings.These defects were closely related to the flow in the cavity.Low permeable investment caused few casting defects despite the cavity type.

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Language：English   Publisher：Ceramic Soc of Japan  

A pure AlN powder was synthesized continuously at 1150-1500 °C by the floating nitridation technique. The nitriding temperature was reduced about 200 °C by using N2 as floating gas for Al powder and injecting an N2/NH3 gas mixture at the center of the heating zone. The AlN powder obtained at 1300 °C had a size of about 10 μm and specific surface area of 24.2 m2/g. AlN particles were so brittle that they were easily crushed to below 0.1 μm. This AlN powder had good flowability and sinterability, and transparent AlN ceramics were obtained by hot-pressing at 1900 °C without any sintering aids. A percentage conversion decreased rapidly with increase in NH3 concentration when an N2/NH3 gas mixture was used as floating gas. The nitriding rate depended strongly on the cracks formed on the particle surface, but not on the diffusion of nitrogen through the surface AlN layer.

DOI： 10.2109/jcersj.102.1032

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Language：Japanese   Publisher：The Japan Prosthodontic Society  

Nitrides used in this experiment are h-BN, AIN and Si_3N_4. The feasibility of using the nitrides was studied as wax pattern coating materials for a Co-Cr alloy in an atmosphere of argon. Wax patterns were painted with the nitride coating material (first investing), and then it was outer-invested witla a mixture of gypsum-bonded investment and water (second investing). The temperature of mold was 700℃, and the thin specimens were cast with an argon arc vacuum-pressure casting machine in the Co-Cr alloy (composition Co : 63 wt%, Cr : 27, Mo : 5, Bat. : 5 ; melting point : 1,380℃). Surfaces of cast specimens were investigated with the unaided eye, a scanning electron microscope, a surface roughness analyzer, an X-ray diifractometer and a micro-Vickers hardness tester. Furthermore, the cast clasp using an h-BN coating material were made and investigated with the unaided eye. Results were sumcmarized as follows : 1. The nitrides inhibited remarkably a reactiona between the cast specimen and the investment. 2. BN had the good effect of separation. 3. The cast surface coated BN had less clitaging than uncoated one. This indicated that cleansability and work efficiency were improved. 4. The surface roughness (Rz) of the specimens decreased to 32, 42 and 60% of the control with BN, Si_3N_4 and AlN, respectively. 5. A hardness change of the alloy by casting was the least in the case of using BN. 6. BN also had the effect in fabricating a cast clasp in the clinical form.

DOI： 10.2186/jjps.34.1235

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Language：Japanese   Publisher：一般社団法人日本歯科理工学会  

コーヌス外冠を高精度に製作するため, 内冠上に外冠をワックス形成し, 内冠ごと埋没, 鋳造する方法が報告されている.この製作法では, 鋳造時の内外冠の溶着等の防止が必要となるため, 外冠のワックス形成前に(1)内冠上に分離材を施す, (2)内冠上に高温酸化による分離膜を生成させる, という2つの手法が用いられている.本法に関する従来の報告は, 術式について述べたものが若干あるだけで, 基礎的な研究はほとんど行われていない.ところで, 演者らの, 窒化物セラミックスの応用による歯科鋳造の改善に関する研究によれば六方晶窒化ホウ素(h-BN)を上述(1)の分離材に応用できる可能性は高い.そこで今回は分離材として, h-BNおよび本法の専用分離材として市販されているPGAを選択し, その効果について検討した.また, 内冠に相当する鋳造体に局部的隆起現象が観察されたので報告する.

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Language：Japanese   Publisher：The Japan Prosthodontic Society  

Nitrides used in this experiment are hBN, AIN and Si3N). We studied feasibility of nitrides as wax pattern coating materials for Co-Cr alloy in an atmosphere of argon. Wax patterns were painted with coating material of nitrides (first investing), then a mixture of phosphate bonded investmetat and water was used in outer investing (second investing). The temperature of mold was 800'C, antd an argon arc vacuum-pressure casting machine was used. We cast the thin specinnens in Co-Cr alloy (composition Co : 63 wt%, Cr : 27wt%, Mo : 5wt%,Bal. : 5wt% ; melting point : 1,380℃). Surfaces of cast specimens were investigated using theunaided eye, a scanning electron microscope and a surface roughness analyzer. Furthermore, the thick specimens (globular form : φ6.5mm) using coatiuag material of hBN were investigated using the unaided eye. Results were summarized as follows ; 1. The nitrides controlled remarkably the reaction between cast specimen and investment. 2. The nitrides had the good effect of separation. 3. The cast surface coated the nitrides had less clinging than uncoated one, and this indicated that its cleansability was improved. 4. The nitrides decreased the surface roughness (Rz) of the cast to about 1/3. 5. hBN had the best effect in nitrides. 6. hBN also had the effect in a thick globular specimen.

DOI： 10.2186/jjps.33.64

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Nitrides used in this experiment are BN, A IN and Si_3N_4. First, we studied wettability between nitrides and molten Au-Au-Pd alloy (comrosition Au : 12 wt%, Ag : 45 wt%, Cu :18 wt%, Pd : 20 wt%, Bal. : 5 wt% ; melting point : 930℃). Secondly, we studied feasibility of nitrides as coating materials for wax patterns, that is, Au-Ag-Pd alloy was cast after painting wax patterns with coating material of nitrides. The temperature of mold was 700℃, and an argon arc vacuum-pressure casting machine was used. Surfaces of casted material were investigated using a scanning electron microscope, X-ray diffractometer and surface roughness analyzer. Results were summarized as follows ; 1. The nitrides little wetted molten Au-Ag-Pd alloy. 2. The color of the cast surface coated BN was purple with a dash of red, and this was derived from Cu_2O. 3. The dense coating layer of BN inhibited formation of CuO on the cast surface and reduced the surface roughness of the cast. 4. The cast surface coated the nitrides had less clinging than uncoated one, and this indicated that its cleansability was improved.

DOI： 10.2186/jjps.32.43

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Venue：福岡・九州大学医学部百年講堂  

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Language：Japanese   Presentation type：Poster presentation  

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Language：Japanese   Presentation type：Poster presentation  

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Language：English   Presentation type：Symposium, workshop panel (public)  

Venue：Nagoya Congress Center (名古屋国際会議場), Nagoya  

113

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Language：Japanese   Presentation type：Poster presentation  

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Language：English   Presentation type：Poster presentation  

Venue：Hawai'i Convention Center, Honolulu, HI USA  

97

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Language：Japanese   Presentation type：Poster presentation  

Venue：山形・米沢・山形県立置賜広域文化施設  

92

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Language：English   Presentation type：Poster presentation  

Venue：Makuhari Center and Prince Hotel, Chiba, Japan  

88

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Language：Japanese   Presentation type：Poster presentation  

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Language：Japanese   Presentation type：Poster presentation  

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Country：Japan

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Award type：Honored in official journal of a scientific society, scientific journal  Country：Japan

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Country：Japan

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Award type：Honored in official journal of a scientific society, scientific journal  Country：Japan

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Country：Japan

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