Hisashi Doi

Tokyo Medical and Dental University, Edo, Tōkyō, Japan

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Publications (108)205.86 Total impact

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    ABSTRACT: To study the allergenic properties of titanium (Ti), the corrosion behaviors and following metal ions release of Ti and nickel (Ni) in simulated physiological environments were investigated. Anodic polarization tests and accelerated dissolution tests were performed in artificial saliva with and without fluorine, and in artificial sweat. Ti showed good corrosion resistance in the artificial saliva without fluorine even when the passive film was physically destroyed by mechanical wear. The concentration of Ti ions released into the solution showed relatively higher values in artificial saliva with fluorine and in artificial sweat, however, it remained to be below 10 ppm. On the other hand, Ni was not passivated in these solutions and the concentrations of the released Ni ions were about 100 ppm. Thus, Ti can be regarded as a considerably safer material than Ni from the viewpoint of corrosion engineering. The large differences in the corrosion characteristics and metal ion solubility between Ti and Ni under the experimental conditions are discussed.
    Preview · Article · Dec 2015 · Electrochemistry -Tokyo-
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    ABSTRACT: In this study, osteogenic differentiation and calcification of preosteoblast (MC3T3-E1) cultured on sputter-deposited titanium (Ti), zirconium (Zr), and gold (Au) on cover glasses were evaluated to understand the differences in bone formation ability among these three metals; these metals show the same high corrosion resistance, but Ti and Zr are covered by surface passive oxide film while Au is not covered by the oxide film. Ti and Zr promoted cellular proliferation without osteogenic differentiation. Cells cultured on Ti and Zr expressed higher levels of Runx2, Col1α1, and Akp2 at an earlier stage, which indicated faster promotion of osteogenic differentiation, as compared to those cultured on Au. Moreover, after 21 days of culture, the Bglap1 and Ifitm5 expression peaks in cells cultured on Ti and Zr were higher than those in cells cultured on Au, which indicated faster promotion of calcification. Cells cultured on Ti showed an advantage in osteogenic differentiation at an early stage, while cells on Zr showed better calcification promotion with a long-term culture. The amount of extracellular calcified deposits was in good agreement with the gene expression results. On the other hand, the intracellular calcium content of cells on Au specimens was higher than that of cells on Ti and Zr specimens. The results indicate that preosteoblasts on Ti and Zr showed faster osteogenic differentiation and calcification than those on Au, whereas Au improved the intracellular calcium content. This article is protected by copyright. All rights reserved.
    No preview · Article · Oct 2015 · Journal of Biomedical Materials Research Part A
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    ABSTRACT: To confirm similarity of hard tissue compatibility between titanium and zirconium, calcification of MC3T3-E1 cells on titanium and zirconium was evaluated in this study. Mirror-polished titanium (Ti) and zirconium (Zr) disks and zirconium-sputter deposited titanium (Zr/Ti) were employed in this study. The surface of specimens were characterized using scanning electron microscopy and X-ray diffraction. Then, the cellular proliferation, differentiation and calcification of MC3T3-E1 cells on specimens were investigated. The surface of Zr/Ti was much smoother and cleaner than those of Ti and Zr. The proliferation of the cell was the same among three specimens, while the differentiation and calcification on Zr/Ti were faster than those on Ti and Zr. Therefore, Ti and Zr showed the identical hard tissue compatibility according to the evaluation with MC3T3-E1 cells. Sputter deposition may improve cytocompatibility.
    No preview · Article · Oct 2015 · Dental Materials Journal
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    ABSTRACT: A large-scale ingot of Zr-1Mo alloy was produced for industrial manufacturing to investigate whether it is possible to produce an ingot with homogeneity. The homogeneous ingot with a chemical composition of Zr-1 mass%Mo was prepared successfully. The microstructure, mechanical properties, and magnetic susceptibility were evaluated. The microstructure showed a coarse colony structure of a plate-like α phase and a thin β phase. An ω phase precipitation was observed in the β phase. Elongation of 23% and magnetic susceptibility of 12.4 × 10-9m3 kg-1 (0.98 × 10-6 cm3 g-1) were achieved. We found that it is possible to produce a homogeneous large-scale ingot of Zr-1Mo with high elongation and low magnetic susceptibility.
    No preview · Article · Sep 2015 · MATERIALS TRANSACTIONS
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    ABSTRACT: The aim of this study was to investigate the bond strength of dental porcelain and the preheated Zr-14Nb alloy, and compare this strength with that of titanium. White oxide layers, which were predominantly composed of monoclinic zirconia, were formed on the preheated sample groups, and exhibited a greater roughness than the control samples. At the metal-ceramic interface, a greater Nb diffusion range was observed than in the control samples. The bond strengths of the samples subjected to 20min preheating treatment were the lowest (33.6±3.2MPa), which may be ascribed to the formation of a brittle thick oxide layer under excessive heat treatment. The samples subjected to this heat treatment for 5min exhibited the highest mean bond strength (43.7±5.9MPa), which was significantly higher than that of titanium (35.3±3.5MPa). Thus, the Zr-14Nb alloy is a promising candidate for fixed dental prosthesis, as long as the appropriate treatment conditions are adopted. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Full-text · Article · Aug 2015
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    ABSTRACT: The Ti–6Al–7Nb alloy is considered a promising material for biomedical applications as it is free of V, which is replaced with Nb for better biocompatibility. This Ti alloy was processed by high-pressure torsion (HPT) at room temperature to refine the grain size to ~100 nm. The Vickers microhardness was increased from 325 HV at the initial as-annealed state to 385 HV after the HPT processing. The HPT-processed samples were deformed under tension at 1073 K (~0.58Tm, Tm is the melting point) with an initial strain rate in the range of 10–4 to 10–2 s–1. The HPT-processed sample through 5 revolutions exhibited an excellent superplastic elongation of 930% at an initial strain rate of 2×10−3 s−1. To conclude, HPT processing is effective in achieving superplasticity of the Ti–6Al–7Nb alloy.
    No preview · Article · Jul 2015 · Materials Science and Engineering A
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    Full-text · Dataset · Mar 2015
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    ABSTRACT: Most orthodontic equipment is fabricated from alloys such as stainless steel, Co-Cr and Ni-Ti because of their excellent elastic properties. In recent years, increasing esthetic demands, metal allergy and interference of metals with magnetic resonance imaging have driven the development of non-metallic orthodontic materials. In this study, we assessed the feasibility of using three super engineering plastics (PEEK, PES and PVDF) as orthodontic wires. PES and PVDF demonstrated excellent esthetics, although PEEK showed the highest bending strength and creep resistance. PEEK and PVDF showed quite low water absorption. Because of recent developments in coloration of PEEK, we conclude that PEEK has many advantageous properties that make it a suitable candidate for use as an esthetic metal-free orthodontic wire.
    Full-text · Article · Feb 2015 · Dental Materials Journal
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    ABSTRACT: To understand the bone formation ability of constituent metal elements of new titanium alloys, titanium, zirconium, niobium, and tantalum, these metals were immersed in various electrolytes containing calcium and/or phosphate ions and characterized using X-ray photoelectron spectroscopy. In addition, cathodic polarization of the metals in the electrolytes was performed to evaluate the stability of the surface oxide films on the metals in the electrolyte. The calcium phosphate layer formed on Ti in electrolytes containing calcium and phosphate ions is relatively protective against mass transfer throughout the layer. However, the zirconium phosphate layer formed on Zr is much more protective and stable than that on Ti. Therefore, calcium ions were not incorporated. Nb and Ta formed calcium phosphate, but the amount was smaller than that in Ti, because phosphates formed on Nb and Ta are somewhat protective and the incorporation of the calcium ion is inhibited. Titanium played the most important role in forming calcium phosphate, while zirconium inhibited the formation of calcium phosphate on titanium alloys. The control of bone formation is feasible by the design of titanium alloys.
    No preview · Article · Jan 2015 · Surface and Interface Analysis
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    ABSTRACT: Ti-6Al-7Nb was deformed by high-pressure torsion to improve the mechanical properties of the alloy. high-pressure torsion was conducted at room temperature under pressures of 2 and 6 GPa for disk-shaped specimens. Microstructure was characterized by transmission electron microscopy (TEM) and X-ray diffraction analysis (XRD). Mechanical properties were evaluated by tensile test and Vickers microhardness measurement. The grain size was refined to about 100 nm after high-pressure torsion processing under 6 GPa through 5 revolutions. Hardness increased with straining by high-pressure torsion and the values after high-pressure torsion processing under 6 GPa were higher than those under 2 GPa. Tensile strength after high-pressure torsion processing of all conditions was higher than that before high-pressure torsion processing. It was found that microstructure and mechanical properties were improved by high-pressure torsion processing.
    Preview · Article · Dec 2014 · Procedia Engineering
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    ABSTRACT: The purpose of this study was to evaluate mechanical properties, surface characteristics and castability of Zr-14Nb dental castings. The mean 0.2% proof and ultimate tensile strengths of Zr-14Nb were approximately 68% and 76% those of Ti-6Al-7Nb, respectively, while they were comparable to Co-29Cr-6Mo. Elongation of Zr-14Nb was the highest of all alloys tested. The hardened reaction layer was formed on the surfaces of the Zr-14Nb castings. The layer consisted of oxygen and aluminum originating form investment. The castability of Zr-14Nb was comparable to that of Ti-6Al-7Nb. Dental castings of Zr-14Nb reveal mechanical properties that were within the range of the other dental alloys. Further improvements in castability and minimization of the surface reaction layer are needed for applications in dental prostheses.
    Full-text · Article · Oct 2014 · Dental Materials Journal
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    ABSTRACT: This study aimed to develop a novel abutment material with good esthetic and mechanical properties by producing a white oxide layer on a zirconium-14 mass%niobium (Zr-14Nb) alloy substrate using a thermal oxidation process. Oxidation temperatures ranged 700-1000°C and oxidation time ranged 30-180 min. The color of the oxide layer varied depending on temperature and time. A white oxide layer was obtained under appropriate conditions. The oxide layer thickness increased with increased temperature and time, as revealed by scanning electron microscopy with energy-dispersive X-ray spectroscopy. Moreover, X-ray diffraction and X-ray photoelectron spectroscopy revealed that the oxide layer was predominantly monoclinic ZrO2, tetragonal ZrO2, and Nb2O5. The oxide layer revealed good abrasion resistance and high adhesion to the substrate. This novel process for producing white materials with good mechanical properties will be useful for abutments and prostheses in dental implant treatment.
    No preview · Article · Jul 2014 · Dental Materials Journal
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    ABSTRACT: Although the reported percentage of bone-implant contact is far lower than 100%, the cause of such low levels of bone formation has rarely been investigated. This study tested the negative biological effect of hydrocarbon deposition onto titanium surfaces, which has been reported to be inevitable. Osteogenic MC3T3-E1 cells were cultured on titanium disks on which the carbon concentration was experimentally regulated to achieve carbon/titanium (C/Ti) ratios of 0.3, 0.7, and 1.0. Initial cellular activities such as cell attachment and cell spreading were concentration-dependently suppressed by the amount of carbon on the titanium surface. The osteoblastic functions of alkaline phosphatase activity and calcium mineralization were also reduced by more than 40% on the C/Ti (1.0) surface. These results indicate that osteoblast activity is influenced by the degree of hydrocarbon contamination on titanium implants and suggest that hydrocarbon decomposition before implant placement may increase the biocompatibility of titanium.
    Full-text · Article · May 2014 · Journal of Dental Research
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    M. MAEKAWA · T. WADA · Z. KANNO · T. HONGO · H. DOI · T. HANAWA · M. UO · T. ONO
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    ABSTRACT: Objective: Most orthodontic equipment have been made of alloys because of its excellent elastic properties. However, the non-metallic orthodontic equipment have been desired from the viewpoint of the esthetics and the prevention of metal allergy. In this study, three types of the super engineering plastics (Poly Ether Ether Ketone: PEEK; Poly Ether Sulfone: PES; Poly Vinylidene Difluoride: PVDF), which have high mechanical and thermal properties, were applied for the orthodontic wires. Our objective is to estimate the mechanical properties of these new wires. Methods: The trial square (1.0×1.0 mm) wires of PEEK, PES and PVDF were prepared and applied for the mechanical test. The rectangular metal wires (0.40×0.55 mm) of SS (3M Unitek, USA), Co-Cr (TOMY, Japan), Ti-Mo (ORMCO, USA) and Ni-Ti (TOMY, Japan) wires were also tested. Three-point bending test was carried with the universal testing machine (AG-IS 500N, Shimadzu, Kyoto, Japan) under 14 mm span. Torsional properties of the PEEK, PES, PVDF, SS and Ni-Ti wires were also estimated (RTC-1210A, ORIENTEC, Tokyo, Japan) with measuring the torsional moment as a function of torsional angle. Results: The wire made with PEEK showed good flexural and torsion strength and those properties were similar to those of Ni-Ti wire. Although the wires made with PES and PVDF showed lower mechanical properties than PEEK, their transparency and esthetics were higher. In addition, those plastic wires all showed lower permanent deformation after 2mm bending test. Conclusion: The super engineering plastics could be applicable for the esthetic orthodontic wires.
    Full-text · Conference Paper · Aug 2013
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    ABSTRACT: Susceptibility artifacts generated in magnetic resonance (MR) images were quantitatively evaluated for various metals using a three-dimensional (3D) artifact rendering to demonstrate the correlation between magnetic susceptibility and artifact volume. Ten metals (stainless steel, cobalt-chromium alloy, niobium, titanium, zirconium, molybdenum, aluminum, tin (Sn), copper (Cu) and silver (Ag)) were prepared, and their magnetic susceptibilities measured using a magnetic balance. Each metal was embedded in a nickel-doped agarose gel phantom and the MR images of the metal-containing phantoms were taken using 1.5 and 3.0 Tesla MR scanners under both fast spin echo and gradient echo conditions. 3D renderings of the artifacts were constructed from the images and the artifact volumes were calculated for each metal. The artifact volumes of metals decreased with decreasing magnetic susceptibility, with the exception of Ag. Although Sn possesses the lowest absolute magnetic susceptibility (1.8×10(-6)), the artifact volume from Cu (-7.8×10(-6)) was smaller than that of Sn. This is because the magnetic susceptibility of Cu was close to that of the agarose gel phantom (-7.3×10(-6)). Since the difference in magnetic susceptibility between the agarose and Sn is close to that between the agarose and Ag (-17.5×10(-6)), their artifact volumes were almost the same, although they formed artifacts that were reversed in all three dimensions.
    Full-text · Article · May 2013 · Acta biomaterialia
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    ABSTRACT: The selective laser melting (SLM) process was applied to a Co-29Cr-6Mo alloy, and its microstructure, mechanical properties, and metal elution were investigated to determine whether the fabrication process is suitable for dental applications. The microstructure was evaluated using scanning electron microscopy with energy-dispersed X-ray spectroscopy (SEM-EDS), X-ray diffractometry (XRD), and electron back-scattered diffraction pattern analysis. The mechanical properties were evaluated using a tensile test. Dense builds were obtained when the input energy of the laser scan was higher than 400Jmm(-3), whereas porous builds were formed when the input energy was lower than 150Jmm(-3). The microstructure obtained was unique with fine cellular dendrites in the elongated grains parallel to the building direction. The γ phase was dominant in the build and its preferential 〈001〉 orientation was confirmed along the building direction, which was clearly observed for the builds fabricated at lower input energy. Although the mechanical anisotropy was confirmed in the SLM builds due to the unique microstructure, the yield strength, UTS, and elongation were higher than those of the as-cast alloy and satisfied the type 5 criteria in ISO22764. Metal elution from the SLM build was smaller than that of the as-cast alloy, and thus, the SLM process for the Co-29Cr-6Mo alloy is a promising candidate for fabricating dental devices.
    Full-text · Article · Feb 2013
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    ABSTRACT: To enhance hard-tissue compatibility of Ti, galvanic current between titanium ( Ti) and gold ( Au) may be available. Prior to the design of medical devices with the capability to generate a galvanic current, it is necessary to understand the control mechanism. In this study, we first measured galvanic current between Ti and Au with various surface areas in Hanks' solution. The galvanic current increased immediately after connection of two electrodes, followed by an abrupt decrease and a steady state. The galvanic current varied with the combinations of Ti and Au areas. We, thereafter, evaluated the formation of calcium phosphate on Ti under a condition of applying simulated galvanic current. Surface characterization was revealed in which the calcium phosphate formation was enhanced accompanied by growth of Ti oxide layer under the galvanic current application. A similar result was observed on Ti with patterned Au coating without outer electric power. Therefore, galvanic current is useful to enhance hard-tissue compatibility, and this technique has potential for applications to metallic biomaterials.
    No preview · Article · Jan 2013 · MATERIALS TRANSACTIONS
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    ABSTRACT: Micro-arc oxidation (MAO) was performed on a β-type Ti–29Nb–13Ta–4.6Zr alloy (TNTZ) in this study to improve its bioactivity in a body fluid and its hard-tissue compatibility. The surface oxide layer formed on TNTZ by MAO treatment in a mixture of calcium glycerophosphate and magnesium acetate was characterized using various surface analyses. The oxide layer was mainly composed of two types of TiO2 (rutile and anatase), and it also contained Ca, P, and Mg, which were incorporated from the electrolyte during the treatment. The calcium phosphate formation on the surface of the specimens after immersion in Hanks’ solution was evaluated to determine the bioactivity of TNTZ with and without MAO treatment. As a result, thick calcium phosphate layers formed on the TNTZ specimen that underwent MAO treatment, whereas only a small amount of precipitate was observed on TNTZ without treatment. Thus, the MAO treatment is a promising method to improve the bioactivity and hard-tissue compatibility of TNTZ.
    No preview · Article · Dec 2012 · Applied Surface Science
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    ABSTRACT: The magnetic susceptibility of cold-rolled Zr-14Nb was evaluated to apply a new metallic medical device used for magnetic resonance imaging (MRI). The magnetic susceptibility of cold-rolled Zr-14Nb decreased up to the reduction ratio of 30%, followed by a gradual decrease up to the ratio of 90%. The TEM observation revealed the strain-induced ω phase formation after cold rolling at the reduction ratio of 5%, indicating that the initial decrease of magnetic susceptibility was caused by the formation of the ω phase. The formation of the ω phase was saturated at the reduction ratio of 30%. The formation of the ω phase was explicable on the basis of the increase of the Young's modulus and Vickers hardness of cold-rolled Zr-14Nb. The effect of texture formation was not obvious for these properties in cold-rolled Zr-14Nb. The magnetic susceptibility of Zr-14Nb can be reduced by applying cold rolling, because of the formation of the strain-induced ω phase, to as low as that of as-cast Zr-9Nb, which is one-third that of Ti and Ti alloys. Therefore, the cold-workable Zr-14Nb with low magnetic susceptibility could be a promising alloy for medical devices under MRI.
    No preview · Article · Nov 2012 · Acta biomaterialia
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    ABSTRACT: Surface modification techniques affect phase transformation which in turn influences strength of zirconia biomaterial. The study aimed at evaluating the tetragonal to monoclinic (t-m) phase transition of zirconia occurring after sandblasting three different ceramic abrasive materials and its subsequent effect on the strength. Zirconia bars (n=24) were sandblasted using silicon carbide (SiC), alumina (Al2O3) and zirconia (ZrO2) particles. After surface characterization by a scanning electron microscope (SEM) and a laser profilometer, the relative amount of transformed monoclinic (m) phase was analyzed by X-ray diffractometry (XRD) and its corresponding effect on the flexural strength and fatigue strength were determined. Data were analyzed using one-way analysis of variance ANOVA (p<0.05). Furthermore, Weibull statistics was used to analyze the variability of flexural strength. The highest amount of monoclinic content was found after sandblasting with SiC consequently resulting in an increased flexural strength and fracture resistance under cyclic load conditions. Weibull modulus was reduced in all the groups with SiC blasting showing the least degradation of m values. The strengthening mechanism that is attributed to sandblasting procedure is influenced by the abrasive material used.
    No preview · Article · Nov 2012 · Bio-medical materials and engineering