Fabrications of zinc-releasing biocement combining zinc calcium phosphate to calcium phosphate cement.

Recently, zinc-releasing bioceramics have been the focus of much attention owing to their bone-forming ability. Thus, some types of zinc-containing calcium phosphate (e.g., zinc-doped tricalcium phosphate and zinc-substituted hydroxyapatite) are examined and their osteoblastic cell responses determined. In this investigation, we studied the effects of zinc calcium phosphate (ZCP) derived from zinc phosphate incorporated into calcium phosphate cement (CPC) in terms of its setting reaction and MC3T3-E1 osteoblast-like cell responses. Compositional analysis by powder X-ray diffraction analysis revealed that HAP crystals were precipitated in the CPC containing 10 or 30wt% ZCP after successfully hardening. However, the crystal growth observed by scanning electron microscopy was delayed in the presence of additional ZCP. These findings indicate that the additional zinc inhibits crystal growth and the conversion of CPC to the HAP crystals. The proliferation of the cells and alkaline phosphatase (ALP) activity were enhanced when 10wt% ZCP was added to CPC. Taken together, ZCP added CPC at an appropriate fraction has a potent promotional effect on bone substitute biomaterials.

Journal of the Mechanical Behavior of Biomedical Materials


Magnetic susceptibility and hardness of Au-xPt-yNb alloys for biomedical applications


Effects of colloidal silica suspension mixing on porosity of phosphate-bonded investments after setting and heating processes

A numerical simulation model, which was based on the setting and heating reactions of the binder phase of phosphate-bonded investment compacts, was developed to compute the porosities of set and burnout compacts. Densities and concentrations of microsilica particles in dilute suspension were measured and input into the simulation model. Validity of the model was confirmed by experimental results, that is, colloidal silica suspensions were prepared using different silica concentrations and mixed with investment powders. Porosities of these set and burnout compacts were experimentally measured. Effects of these factors on the porosity of compacts were examined using the developed simulation model: liquid/powder (L/P) ratio, concentration of microsilica particles in colloidal silica suspension, and ratio of binder component (NH4H2PO4) in investment powder. It was concluded that numerical simulation is a viable tool for dental materials research.


Formability and mechanical properties of porous titanium produced by a moldless process

Tailor-made porous titanium implants show great promise in both orthopedic and dental applications. However, traditional powder metallurgical processes require a high-cost mold, making them economically unviable for producing unique devices. In this study, a mixture of titanium powder and an inlay wax binder was developed for moldless forming and sintering. The formability of the mixture, the dimensional changes after sintering, and the physical and mechanical properties of the sintered porous titanium were evaluated. A 90:10 wt % mixture of Ti powder and wax binder was created manually at 70°C. After debindering, the specimen was sintered in Ar at 1100°C without any mold for 1, 5, and 10 h. The shrinkage, porosity, absorption ratio, bending and compressive strength, and elastic modulus were measured. The bending strength (135-356 MPa), compression strength (178-1226 MPa), and elastic modulus (24-54 GPa) increased with sintering time; the shrinkage also increased, whereas the porosity (from 37.1 to 29.7%) and absorption ratio decreased. The high formability of the binder/metal powder mixture presents a clear advantage for fabricating tailor-made bone and hard tissue substitution units. Moreover, the sintered compacts showed high strength and an elastic modulus comparable to that of cortical bone.

Journal of Biomedical Materials Research. Part B, Applied Biomaterials


埋没材の加熱法について考える

埋没材の加熱法について考える


Calcium phosphate-based cements: clinical needs and recent progress

Journal of Materials Chemistry. B, Materials for Biology and Medicine


Porosity of dental phosphate-bonded investments after setting and heating processes

Porosities of set and burnout compacts of phosphate-bonded investments were determined. A gas pycnometer was used to measure the volumes, and hence the densities, of fine powders and porous compacts. Porosities of set and burnout compacts were then obtained from these data for as-received powders and dry set compacts by a numerical simulation method, subsequently leading on to the estimated compositions of conventional and rapid-heating investments used in this study. Excess water content in the hardening investment compact was evaluated as a function of setting time elapsed from the start of mixing. Porosities were about 24-32% for set compacts and 43% for burnout compacts, which well agreed with the numerically computed results. It was concluded that the functional composition of investment powder needed to achieve the optimal porosity as well as process parameters such as water-powder (W/P) ratio and keeping time of mixed investment casting slurry before heat treatment could be determined using the numerical simulation method developed in this study.


Evaluation of newly developed bone cement introducing Strontium consistencies for bone regenerative substitute

Transactions of the Japanese Society for Medical and Biological Engineering


Correlation in the mechanical properties of acrylic denture base resins

The aim of the present study was to measure various mechanical properties of acrylic denture base resins, including flexural modulus, flexural strength, fracture toughness, Barcol and Vickers hardness and their related properties, and to investigate correlations between different mechanical properties. Resin specimens were prepared according to manufacturers' recommended instructions. The mechanical properties were measured under specified standards. Data from the mechanical tests were examined using correlation tests. In general, the mean results for mechanical properties of each specimen group were differently ranked depending on the tested mechanical property. The flexural modulus value showed strong or reasonable positive correlation with those of proportional limit, flexural strength, and surface hardness. In contrast, fracture toughness revealed strong negative correlations with the flexural parameters and hardness values. Results of correlation tests for the different parameters can be used for estimation of mechanical performance of acrylic denture bases in clinical situation and for quality control purposes.


Porosity of dental gypsum-bonded investments in setting and heating process

The porosity of gypsum-bonded investments for set and heated compacts was measured and theoretically computed quantitatively, because porosity is an effective factor for determining the strength, setting/heating expansion, and permeability of compacts at casting. A helium gas pycnometer was used to measure the solid volume of fine powders, powder-water mixtures, and porous compacts. The compositions of the conventional cristobalite investment and rapid-heating type investment were estimated from the measured solid densities of the as-received powders and the set investments. The porosity and water content of the set investments were determined from the experimental data. Excess water content in the set investment was calculated in relation to the elapsed time from the start of mixing with water. The experimental porosities of the set and heated investments were about 40% for dry set >compacts and about 50% for fired compacts, which well agreed with the numerically computed estimations, respectively.


A Useful and Non-invasive Microanalytical Method for Dental Restoration Materials


Reinforcement of bond strength of self-etching orthodontic adhesive.

Abstract Objective: To determine the reinforcement of bond strength of a self-etching system by applying a pretreatment agent. Materials and Methods: Sixty extracted human premolars were used in this study. The enamel surfaces were treated with four pretreatment agents?phosphoric acid, polyacrylic acid, citric acid, and ammonium hexafluorosilicate (SiF)?and were examined under a scanning electron microscope. Afterward, orthodontic brackets were bonded with a self-etching adhesive system (n ?=? 10 for each agent), and shear bond strength was measured through a debonding process. The adhesive remnant index (ARI) was also assessed. Results: Enamel surfaces treated with polyacrylic acid seemed almost the same as intact enamel. Treatment with SiF induced slight shallow depressions compared with the intact enamel. On the other hand, enamel surfaces treated with citric acid and phosphoric acid showed severe etching patterns. All pretreatments increased the bond strength, but SiF-treated specimens revealed the greatest strength (12.201 ? 1.048?MPa), followed by polyacrylic acid (12.030 ? 2.103?MPa). The control group with no pretreatment showed the least strength (9.078 ? 1.678?MPa). All pretreatments increased ARI score compared with the control group. Conclusions: Surface conditioning before bracket adhesion could reinforce the bond strength of the self-etching adhesive system, resulting in a more reliable bonding system.


Antibacterial activity of composite resin with glass-ionomer filler particles

The purpose of this study was to examine the antibacterial activity of composite resin with glass-ionomer filler particles versus that of contemporary commercial composite resins. Three composite resins were used: Beautifil II (containing S-PRG filler), Clearfil AP-X, and Filtek Z250. Resin blocks were bonded to maxillary first molars, and plaque accumulation on the resin block surface was examined after 8 hours. For the antibacterial test, the number of Streptococcus mutans in contact with the composite resin blocks after incubation for 12 hours was determined, and adherence of radiolabeled bacteria was evaluated. Less dental plaque was formed on Beautifil II resin block as compared to the other two materials. Antibacterial test revealed that there were no significant differences in the number of Streptococcus mutans among the three composite resins. However, the adherence of radiolabeled bacteria to the saliva-treated resin surface was significantly (p>0.01) lower in Beautifil II than in the other two materials. These results suggested that Beautifil II could reduce dental plaque formation and bacterial adherence, leading to prevention of secondary caries


GM-CSF and IL-4 induce dendritic cell differentiation and disrupt osteoclastogenesis through M-CSF receptor shedding by up-regulation of TNF-{alpha} converting enzyme (TACE)

Monocytes give rise to macrophages, osteoclasts (OCs), and dendritic cells (DCs). M-CSF and RANK ligand induce OC differentiation from monocytes, while GM-CSF and IL-4 trigger monocytic differentiation into DCs. These two differentiation pathways occur in a mutually exclusive manner. However, regulatory mechanisms for the polarization of monocytic differentiation are still unclear. The present study was undertaken to clarify the mechanism of triggering the deflection of OC and DC differentiation from monocytes. GM-CSF and IL-4 abolished monocytic differentiation into OCs while inducing DC differentiation even in the presence of M-CSF and RANK ligand. GM-CSF and IL-4 in combination potently up-regulate TNF-alpha converting enzyme (TACE) expression and activity in monocytes, causing ectodomain shedding of the membrane-bound M-CSF receptor, resulting in the disruption of its phosphorylation by M-CSF as well as the induction of osteoclastogenesis from monocytes by M-CSF and RANK ligand. Interestingly, TACE inhibition robustly causes the resumption of the surface expression of M-CSF receptors on monocytes, which facilitates M-CSF-mediated phosphorylation of M-CSF receptors and macrophage/OC differentiation while impairing GM-CSF and IL-4-mediated DC differentiation from monocytes. These results reveal a novel proteolytic regulation of M-CSF receptor expression in monocytes to control M-CSF signaling and monocytic differentiation into macrophage/OC-lineage cells or DCs.


Enamel bonding of self-etching and phosphoric acid-etching orthodontic adhesives in simulated clinical conditions: Debonding force and enamel surface

This study aimed to evaluate the effectiveness of self-etching and phosphoric acid-etching orthodontic adhesives for enamel bonding in simulated clinical conditions. By using two self-etching (Transbond Plus, TP; Beauty Ortho Bond, BB) and two acid-etching (Transbond XT, TX; Superbond Orthomite, SB) adhesives, orthodontic brackets were bonded on human premolars (n=10 for each adhesive). Ten teeth without bracket bonding, i.e., intact enamel surfaces, were used as control for SEM observation. After 7-day storage in lactic acid solution, bracket debonding force by means of debonding pliers, adhesive remnant index (ARI), and enamel surface morphology were examined. All the tested adhesives exhibited sufficient bond strength for clinical use. The ARI scores were almost the same among the four adhesives. In terms of SEM observation, the enamel surfaces in the control and TP groups showed a slight change after immersion in lactic acid solution, while the BB group showed less change on the enamel surface compared with the TP group. Meanwhile, the two acid-etching adhesives caused considerable demineralization. Taken together, these findings indicated that the action of self-etching systems was evidently more conservative.


Development of a novel cement by conversion of hopeite in set zinc phosphate cement into biocompatible apatite

Synthetic bone cement that has zinc oxide core particles covered with hydroxyapatite (HAP) was developed; that is, the conversion of hopeite, the traditional zinc phosphate cement, into HAP was attempted. Here, hopeite is the final product of the reaction between powders and trituration liquid of the traditional zinc phosphate cement. This cement may have many advantages not only in terms of biological functions but also the setting process of the traditional cement and the mechanical properties of the developed compact if the hopeite can be converted into calcium phosphate (CP). In this study, calcium nitrate solutions of various concentrations were used for the conversion of hopeite crystals into CP. The products after the solution treatment were analyzed by X-ray diffractometry (XRD), Fourier transform infrared spectrometry (FTIR), and scanning electron microscope (SEM) observation. These results indicated that the converted scholzite crystals could be partially detected. Several types of set zinc phosphate cement with different P/L ratios were arranged. The surface products of the set cement after the solution treatment were analyzed by XRD. However, the crystal phase such as hopeite was not detected except for zinc oxide. The set cement, which was treated with the calcium nitrate solution, was immersed in simulated body fluid (SBF). HAP-like crystals on the set cement could be detected for the specimens immersed for 4 weeks. These findings suggested that the binding phase in the set cement could be converted into HAP by immersion in SBF.


Effects of heat treatment on the bioactivity of surface-modified titanium in calcium solution

The purpose of this study was to determine the effects of heat treatment on the bioactivity of hydrothermal-modified titanium in CaO solution for improved bioactivity by immersion in simulated body fluid (SBF). The hydrothermal treatment of titanium in CaO solution was performed at 121 degrees C at 0.2 MPa for 1 h in an autoclave followed by 1 h heat treatments at 200, 400, 600 and 800 degrees C simultaneously. The bioactivity of titanium was evaluated by hydroxyapatite precipitation during immersion in SBF. Surface microstructure changes after the heat treatments and immersion in SBF were determined by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Heat treatments at high temperatures (600 and 800 degrees C) promoted the synthesis of anatase, increased the thickness of the titanium oxide layer on the modified titanium surface and promoted the synthesis of calcium titanate, which possibly promoted the precipitation of apatite in SBF. The extent of precipitations increased with the time of immersion in SBF and the temperature of the heat treatment. Island-like deposits of needle-like crystals were observed only on the surface of the 600 and 800 degrees C heat-treated specimens after two or four week immersions in SBF. The results suggested that treatments of the surface of hydrothermal-treated titanium specimens at high temperatures (600 and 800 degrees C) could be effective for the surface modification of titanium as an implant material offering better osseointegration.


Assessment of allergic hypersensitivity to dental materials

Some metallic materials in dental prostheses may cause allergic hypersensitivity. Symptoms appear not only in the oral cavity, but also on hands, feet or the entire body. Release of metal ions is thought to cause the allergic reactions; micro-particles of the corrosion products of the metal and/or ionic metal hydroxides/oxides may be the allergens. The study purpose was to review clinical surveillance of dental allergic hypersensitivity in our dental hospital. From July 2000 to June 2005, 212 patients with suspected dental metal allergy were patch tested with 26 reagents, including 19 ready-made patch test reagents (Patch test reagents, Torii Pharmaceutical Corporation, Tokyo, Japan) and 9 custom-made reagents. One-hundred-and-sixty-seven patients were females (78.8%) and 45 patients were males (21.2%). A total of 148 patients (69.8%) had one or more positive patch test reactions. The most common allergens were nickel (25.0%), palladium (24.4%), chromium (16.7%), cobalt (15.9%) and stannum (12.5%). Typical allergic symptoms and diagnoses were Pustulosis palmaris et plantaris, lichen planus, stomatitis and contact dermatitis. This study indicates that dentists and dental researchers should be concerned about the allergenic potential of dental metal materials.


Hydrogen-related degradation of mechanical properties of titanium and titanium alloys


Hydrogen embrittlement of Ni-Ti superelastic alloy aged at room temperature after hydrogen charging


Fracture of Ni-Ti superelastic alloy under sustained tensile load in physiological saline solution containing hydrogen peroxide

The fracture of Ni-Ti superelastic alloy has been investigated by a sustained tensile-loading test in physiological saline solution containing hydrogen peroxide (0.15M NaCl + 0.3M H(2)O(2)). The fracture always occurs when the applied stress exceeds the critical stress for martensite transformation. In contrast, under a low applied stress, the fracture does not always occur within 1000 h. The fracture is probably mainly caused by localized corrosion associated with the preferential dissolution of nickel ions. In 0.3M H(2)O(2) solution without NaCl, the fracture does not occur even under a high applied stress. The results of the present study imply that one reason for the fracture of the Ni-Ti superelastic alloy in vivo is localized corrosion due to the synergistic effects of hydrogen peroxide and sodium chloride under applied stress.

Journal of Biomedical Materials Research. Part A


Hydrogen absorption and thermal desorption behaviors of Ni-Ti superelastic alloy subjected to sustained tensile-straining test with hydrogen charging


Charactarization of titanium and its delayed fracture in vivo

チタンのキャラクタリゼーションと生体内での遅れ破壊

Delayed fracture of medical Ti devices was studied by micro-mechanics. Effects of oxygen and hydrogen on the characterization of titanium were discussed in terms of macro and microscopic aspects. Hydrogen can have a major effect on the microstructure and properties of Ti. When the hydrogen concentration exceeds the terminal hydrogen solubility, a titanium hydride phase (TiH_2) can begin to form. Transformation from α-Ti to the hydride phase results in a volume expansion. Hydrides are formed along the grain boundary deeply in the surface. Micro-cracks are formed on the hydrides when an external force is applied. The cracks are developed and accelerate by the mechanism of stress-corrosion cracking related to hydrogen. Experimentally, we confirmed this by fatigue tests of pure Ti and by delayed fracture tests under sustained tensile loading in fluoride ion solutions. The results indicate that stress-corrosion cracking is an effective factor in delayed fracture of Ti.

チタンの医用デバイスにおける遅れ破壊の機構をマイクロメカニクスの立場から紹介した.酸素と水素がチタンのキャラクタリゼーションに及ぼす影響をマクロとミクロの立場から議論した.とくに,水素はチタンの微視組織と性質に大きな影響を及ぼす.水素濃度が固溶限を越えると水素化チタンが形成される.水素化物に変態するとチタンの体積が膨張する.水素化物は表面から結晶の粒界に沿って内部に形成され,引張の外力が作用すると水素化物に亀裂が生じる.この亀裂は水素と関係した応力腐食割れの機構により進展し,遅れ破壊を生じる.純チタンの疲労試験とフッ素イオン含有溶液中での引張応力負荷実験から,この現象を検証し,応力腐食割れがチタンの遅れ破壊の原因であることを明らかにした.

The Journal of the Japanese Society for Dental Materials and Devices


Effects of potential on hydrogen absorption and desorption behaviors of titanium in neutral fluoride solutions


Hydrogen thermal desorption behavior of Ni-Ti superelastic alloy subjected to tensile deformation after hydrogen charging


Effects of surface oxide films on hydrogen absorption and mechanical properties of titanium


Relationship between corrosion and mechanical strength of annealed titanium

チタンの耐食性と機械的性質に及ぼす熱処理の影響

Journal of Japanese Society for Dental Products


Surface modification of titanium with hydrothermal treatment at high pressure

Surface modification of titanium was investigated by means of hydrothermal treatment with a maximum pressure of 6.3 MPa (280 degrees C temperature) in CaO solution or water to improve bioactivity and biocompatibility. As a result, calcium titanate was formed on the titanium surface. Moreover, titanium oxide and titanium hydroxide layers on the surface increased as temperature and pressure increased. The surface-modified titanium was also immersed in a simulated body fluid (SBF) to estimate its bioactivity. Needle-like apatite precipitation was observed on all hydrothermal-treated titanium surfaces after immersion in SBF for four weeks. In particular, the apatite precipitation of titanium treated with 6.3 MPa in CaO solution was clearer and larger in amount than those of all other hydrothermal-treated specimens. Further, the amount of precipitate corresponded to the thickness of the surface-modified layer and the amount of calcium in the surface layer. The results suggested that surface modification of titanium with high-pressure hydrothermal treatment seemed to improve bioactivity and biocompatibility.


Effects of moisture and dissolved oxygen in methanol and ethanol solutions containing hydrochloric acid on hydrogen absorption and desorption behaviors of Ni-Ti superelastic alloy


Fracture of sustained tensile-loaded Ti-0.2% Pd alloy in acid and neutral fluoride solutions


Chemical surface modification of high-strength porous Ti compacts by spark plasma sintering

The biological properties of a titanium (Ti) implant depend on its surface oxide film. The aims of the present study were to increase the specific surface oxide area on Ti using a porous structure and to study the relationship between the amount of apatite coating in simulated body fluid (SBF) and the actual surface area on titanium powders. Ti powders of 110 microm average diameter were sintered by spark plasma sintering. The sintered compacts had a porosity of 28%, a compressive elastic modulus of 7.9 GPa and an ultimate strength of 112 MPa. The compressive strength of the compacts was increased to 588 MPa by subsequent annealing in a vacuum furnace at 1000 degrees C for 24 h. The sintered compacts were treated with aqueous NaOH solution and subsequently heated at 600 degrees C. The pretreated compacts showed apatite crystal precipitation in SBF. The amounts of precipitates through the compacts were compared with those of the Ti plate substrates subjected to the same chemical pretreatment. It was confirmed that the amounts of precipitates through the compacts were more than one hundred times higher than those on the Ti plates. It was concluded that the metal porous compacts developed may be used as functional materials for immobilizing functional proteins and/or drugs, because the precipitated apatite can adsorbed these substances.


Hydrogen absorption of titanium and nickel-titanium alloys during long-term immersion in neutral fluoride solution

Hydrogen absorption of biomedical titanium and Ni-Ti alloys in a neutral fluoride (2.0% NaF) solution for up to 10,000 h at 37 degrees C has been evaluated by means of hydrogen thermal desorption analysis. For alpha titanium (commercial pure titanium), the amount of absorbed hydrogen was, at most, 10-30 mass ppm, and the corrosion product and hydride formation were revealed on the surface of the specimen by X-ray diffraction analysis. Ni-Ti superelastic alloy absorbed approximately 150 mass ppm of hydrogen, which was probably sufficient to result in the pronounced degradation of the mechanical properties, although corrosion was hardly observed. In contrast, hydrogen absorption of alpha-beta titanium (Ti-6Al-4V) and beta titanium (Ti-11.3Mo-6.6Zr-4.3Sn) alloys was negligible, although general corrosion was observed. The results of the present study indicate that the susceptibility of titanium and Ni-Ti alloys to hydrogen absorption in the neutral fluoride solution is different from that in the acidic fluoride solution reported previously.

Journal of Biomedical Materials Research. Part B, Applied Biomaterials


Effect of surface oxide films on degradation of titanium by thermal desorption spectroscopy

昇温脱離分析によるチタンの侵食に対する酸化膜の働きの評価


Strengthening of calcium phosphate cement by compounding calcium carbonate whiskers

The purpose of this study was to investigate how aragonite (calcium carbonate) whiskers influenced the strengthening and carbonating of alpha-tricalcium phosphate (alpha-TCP) based calcium phosphate cement. Aragonite whiskers of 0.95 microm width with an aspect ratio of 6.6 were prepared. The cement powder, alpha-TCP containing 0-50 mass% aragonite whisker, was mixed with 0.6 mol/L NaH2PO4 solution and incubated at 37 degrees C and 100% relative humidity. Diametral tensile strength (DTS) value increased significantly when appropriate amount of aragonaite whiskers was added. For example, DTS value of set cement containing 20 mass% aragonite whisker was 5.8 +/- 0.5 MPa, whereas DTS value of set cement containing no whiskers was 1.3 +/- 0.2 MPa after 1-week incubation. SEM observation revealed that the shape of the whiskers and the densification of the structure could have contributed to the strengthening of the set cement. Moreover, FTIR spectra implied that a bone-like carbonated apatite was precipitated in the cement. The results obtained in the present study revealed that the shape as well as any slight dissolution of aragonite whiskers could contribute to improving the properties of a-TCP based calcium phosphate cement.


Hydrogen embrittlement of Ni-Ti superelastic alloy in ethanol solution containing hydrochloric acid


Susceptibility to delayed fracture of alpha-beta titanium alloy in fluoride solutions


Distribution and thermal desorption behavior of hydrogen in titanium alloys immersed in acidic fluoride solutions


Evaluation of hydrogen absorption properties of Ti-0.2 mass% Pd alloy in fluoride solutions


Hydrogen embrittlement of work-hardened Ni-Ti alloy in fluoride solutions.

Hydrogen embrittlement of work-hardened Ni-Ti alloy has been examined in acidulated phosphate fluoride (APF) solutions. Upon immersion in a 2.0% APF solution with a pH of 5.0, tensile strength decreased markedly with immersion time. Moreover, the fracture mode changed from ductile to brittle due to brittle layer formation at the peripheral part of the cross section of the specimen. The amount of absorbed hydrogen increased linearly with immersion time, and it reached above 5000 mass ppm after 24 h. The hydrogen desorption temperature of the immersed specimens shifted from 450 degrees C to a lower temperature with immersion time. As the amount of absorbed hydrogen was larger than 500 mass ppm, the degradation of mechanical properties was recognized. Although the tensile properties and fracture mode scarcely change in a 0.2% APF solution, the slight reduction in hardness and hydrogen absorption of several hundreds mass ppm were observed. The results of the present study imply that work-hardened Ni-Ti alloy is less sensitive to hydrogen embrittlement compared with Ni-Ti superelastic alloy.


Hydrogen absorption of titanium in acidic fluoride solutions


Degradation in performance of orthodontic wires caused by hydrogen absorption during short-term immersion in 2.0% acidulated phosphate fluoride solution.

The purpose of this study was to investigate the degradation in performance of four major alloys of orthodontic wires, namely nickel-titanium, beta titanium, stainless steel, and cobalt-chromium-nickel, caused by hydrogen absorption during short-term immersion in an acid fluoride solutions. The hydrogen-related degradation of orthodontic wires after immersion in 2.0% acidulated phosphate fluoride solution at 37 degrees C for 60 minutes was evaluated by a tensile test, scanning electron microscope observation, and hydrogen thermal desorption analysis. Upon immersion, the tensile strengths of the nickel-titanium and beta titanium wires decreased. Particularly, the nickel-titanium wire fractured before yielding, and the fracture mode changed from ductile to brittle. The amounts of absorbed hydrogen in the nickel-titanium and beta titanium wires were 200 and 100 mass ppm, respectively. On the other hand, the tensile strengths of the stainless steel and cobalt-chromium-nickel wires were only slightly affected by immersion. The results of this study suggest that degradation in performance of orthodontic wires of titanium alloys occurs because of hydrogen absorption even after a short-term immersion in fluoride solutions.


Effects of constituting phases in Ni-Ti shape memory alloy on susceptibility to hydrogen embrittlement


Delayed fracture of Ni-Ti superelastic alloys in acidic and neutral fluoride solutions.

Hydrogen-related degradation of the mechanical properties of a Ni-Ti superelastic alloy has been examined by means of delayed fracture tests in acidic and neutral fluoride solutions and hydrogen thermal desorption analysis. Delayed fracture took place in both solutions; the time to fracture was shorter in the acidic solutions than in the neutral solutions with the same fluoride concentration. The time to fracture was reduced in both solutions when applied stress exceeded the critical stress for martensite transformation. In the acidic solutions, Ni-Ti superelastic alloy underwent general corrosion and absorbed substantial amounts of hydrogen. Fractographic features suggested that the delayed fracture in the acidic solutions was attributable to hydrogen embrittlement, whereas in the neutral solutions, a different fracture mode appeared associated with localized corrosion only in the vicinity of the fracture initiation area. In the neutral solutions, the amount of absorbed hydrogen was much less than that in the acidic solutions, and the delayed fracture was likely to be induced by active path corrosion accompanying hydrogen absorption. The results of the present study imply that the hydrogen-related degradation of performance of Ni-Ti superelastic alloys occurs in the presence of fluoride.

Journal of Biomedical Materials Research. Part A


Fracture of nickel-titanium superelastic alloy in sodium hypochlorite solution


Porous Ti-6Al-4V alloy fabricated by spark plasma sintering for biomimetic surface modification

Porous compacts with both biological and biomechanical compatibilities and high strength were developed. Spherical powders of Ti-6Al-4V alloy, which were either as received or surface modified with the use of calcium ions by hydrothermal treatment (HTT), were fabricated by a spark plasma sintering process. The porous compacts of pure Ti were used as reference materials. Porosity was approximately 30%, and compressive strengths were 113 and 125 MPa for the as-received Ti alloy powders and those modified by the HTT process, respectively. The bending strength and elastic modulus of as-received Ti alloy powders were 128-178 MPa and 16-18 GPa, respectively. Each of the compacts was immersed in simulated body fluid (SBF). The amount of adsorption/precipitation of calcium phosphate through the compacts was measured by weight change and was observed by SEM. The compacts were covered with calcium phosphate after 2 weeks of immersion in SBF. The compacts of Ti alloy had plenty of precipitated apatite crystals, and modification by HTT accumulated more precipitation. Because calcium phosphate is a mineral component of bone, apatite, which is precipitated on the surface of the compacts, could adsorb proteins and/or drugs such as antibiotics. It is expected that a large amount of proteins and/or drugs could be impregnated when the porous compacts developed are used.

Journal of Biomedical Materials Research. Part B, Applied Biomaterials


Fracture associated with hydrogen absorption of sustained tensile-loaded titanium in acid and neutral fluoride solutions

The fracture of commercial pure titanium in acid and neutral fluoride solutions has been examined by a sustained tensile-loading test and hydrogen thermal desorption analysis. It was found that the fracture of titanium occurred in neutral 2.0% NaF solution as well as in 2.0% acidulated phosphate fluoride (APF) solution. The time to fracture decreased with increasing applied stress in both 2.0% APF and 2.0% NaF solutions. In the case of the same applied stress, the time to fracture in the 2.0% APF solution was shorter than that in the 2.0% NaF solution. General corrosion was exhibited on the side surface of the tested specimens. The formation of sodium titanium fluoride was observed on the surface of the immersed specimens in the 2.0% APF solution. Hydrogen desorption of the tested specimen in the 2.0% APF solution was observed with a peak at approximately 600 degrees C. The amount of absorbed hydrogen was >300 mass ppm in the 2.0% APF solution under an applied stress for 24 h. The results of the present study imply that applying stress to titanium by immersing in fluoride solutions leads to the degradation of its mechanical properties.


Hydrogen absorption behavior of beta titanium alloy in acid fluoride solutions

Hydrogen absorption behavior of a beta titanium alloy in acid fluoride solutions has been analyzed by hydrogen thermal desorption. The amount of absorbed hydrogen increased with immersion time in a 2.0% acidulated phosphate fluoride (APF) solution. In the case of an immersion time of 60 h, the amount of absorbed hydrogen exceeded 10000 mass ppm. In contrast, the amount of hydrogen absorbed in the 0.2% APF solution was several times smaller than that in the 2.0% APF solution for the same immersion time. For immersion in a 0.2% APF solution, hydrogen absorption saturated after 48 h. The surface topography and corrosion products on the surface of the specimen immersed in the 2.0% APF solution were different from those in the 0.2% APF solution. During the later stage of immersion, the amount of absorbed hydrogen markedly increased under higher applied stress, although the applied stress did not enhance hydrogen absorption during the early stage of immersion. These results of hydrogen absorption behavior are consistent with the delayed fracture characteristics of the beta titanium alloy.


Delayed fracture of beta titanium orthodontic wire in fluoride aqueous solutions.


Shape recovery of shape memory alloy fiber embedded resin matrix smart composite after crack repair

Ni-Ti shape memory alloy fiber embedded resin matrix composites were produced for evaluation of "smart denture", a newly developing denture with the function to close its own crack. Their bending strength and shape recovery after instant crack repair was estimated. The embedded fibers did not decrease the bending strength of the composite after repair. The crack closure of the composites was performed well simply by heating at 80 degrees C. Nevertheless, they showed apparent deflection after crack repair. The following two phenomena were supposed to be the main cause of it: the polymerization shrinkage of matrix resin with heating, and the coefficient of the thermal expansion mismatch between the fiber and the matrix. The embedded fibers could close the crack of the matrix with enough high accuracy for specimen repair, but they turned out to change the specimen shape after repair.


Diffusion coefficient of water through dental composite resin

Water sorption of polymer filling materials affects dimensional stability, mechanical properties and bonding strength with tooth structures. To clarify the effect of the degradation on service life and micro-leakage, the diffusion coefficient of water through the resin should be identified. Distributions of time-dependent water concentrations in the resin were computed. Water sorption of composite resin discs with different thicknesses was measured and compared with the solution of Fick's second law. The diffusion coefficient of water through the resin discs was computed to be D=3.9-5.0 x 10(-13)m(2)/s from the measurements of specimens with different thicknesses. Results of water sorption measurements for the discs with different thicknesses were in good agreement with the theoretical results. The relationship among the thickness of the disc, the diffusion coefficient and the water sorption ratio was shown clearly. The testing method for water sorption by International Standard ISO 4049 for resin-based filling materials was discussed.


Degradation of tensile strength of Ni-Ti superelastic alloy due to hydrogen absorption in methanol solution containing hydrochloric acid


Susceptability to delayed fracture of Ni-Ti superelastic alloy


Evaluation of apatite ceramics containing α-tricalcium phosphate by immersion in simulated body fluid

The purpose of this study was to estimate the availability of alpha-tricalcium phosphate (alpha-TCP) on/in hydroxyapatite (HAP) ceramics for bioactivity as bone-substitute materials by immersion in a simulated body fluid (SBF; Hanks' solution) containing ion concentrations similar to those in human blood plasma. Two alpha-TCP-surface-modified HAP and alpha-TCP-HAP composite materials were prepared by orthophosphoric acid treatment of sintered HAP and controlling the crystal phases of calcium phosphate cement, respectively. After immersion in SBF, the sintered HAP modified on the surface in an approximately 0.2 microm alpha-TCP layer was more effective for the precipitation of carbonated apatites than an approximately 2 microm alpha-TCP layer and HAP-only layer. In the calcium phosphate cements consisting of HAP and alpha-TCP phases, after immersion for 1 week, the specimens precipitated large amounts of apatites having alpha-TCP contents of approximately 25% and 50% in the cement. The results of immersion tests imply the possibility that the alpha-TCP on/in HAP ceramics may be a bioactive agent for bone-substituting HAP materials.


Hydrogen embrittlement of Ni-Ti superelastic alloy in fluoride solution

Journal of Biomedical Materials Research


Surface oxide films on titanium alloys regenerated in Hanks' solution


Fracture mechanisms of retrieved titanium screw thread in dental implant

Titanium and its alloy are increasingly attracting attention for use as biomaterials. However, delayed fracture of titanium dental implants has been reported, and factors affecting the acceleration of corrosion and fatigue have to be determined. The fractured surface of a retrieved titanium screw and metallurgical structures of a dental implant system were analyzed. The outer surface of the retrieved screw had a structure different from that of the as-received screw. It was confirmed that a shear crack initiated at the root of the thread and propagated into the inner section of the screw. Gas chromatography revealed that the retrieved screw had absorbed a higher amount of hydrogen than the as-received sample. The grain structure of a titanium screw, immersed in a solution known to induce hydrogen absorption, showed features similar to those of the retrieved screw. It was concluded that titanium in a biological environment absorbs hydrogen and this may be the reason for delayed fracture of a titanium implant.


Surface-layer modification of hydroxyapatite ceramic with acid and heat treatments

The purpose of this study was to examine or characterize the surface layer of a calcium phosphate ceramic with a gradual compositional change from alpha-tricalcium phosphate (alpha-TCP) on the surface to hydroxyapatite (HAP) on the inside. The surface of a dense HAP ceramic was acid-treated for 1 hour with orthophosphoric acid (H3PO4) solutions of several concentrations (0.5, 1.0 and 5.0 mol/L) or a buffered solution (pH 4.0) consisting of phosphate solutions. After acid treatment, specimens were heat-treated at 1,250 degrees C for 1 hour. X-ray photoelectron spectroscopy revealed that the compositional gradient layer could be modified on the surface of the HAP ceramic with all acid and heat treatments, and that 5.0 mol/L H3PO4 solution and heat treatments had a maximal thickness of approximately 2 microm for the surface-modified layer. It was confirmed that the outermost layer of HAP ceramics modified with the treatments, except 5.0 mol/L H3PO4 solution, showed a compound such alpha-TCP.


Hydrothermal modification of titanium surface in calcium solutions

Hydrothermal modification of a titanium surface in calcium solutions was performed. The apatite precipitation on the modified surface in Hanks' solution, as a simulated body fluid, was evaluated and the surface microstructure changes after the modification were characterized by thin-film X-ray diffractometry (TF-XRD) and X-ray photoelectron spectroscopy (XPS). Hydrothermal modification in CaO solution enhanced the precipitation of apatite on the titanium surface. High pH, high pressure and high temperature of the CaO solution increased the thickness of the surface-modified layer and enhanced the synthesis of calcium titanate which possibly promoted the precipitation of apatite in Hanks' solution. Hydrothermal modification in CaCl2 solution, on the other hand, showed reverse effects. The modification of titanium in CaO solution with hydrothermal treatment is expected to result in excellent osteointegration and can be easily performed by using an autoclave, a clinical apparatus widely used.


Hydrogen embrittlements of nickel-titanium alloy in biological environment

Metallurgical and Materials Transactions A


Mechanical properties of glass-only porcelains prepared using two feldspathic-frits with different thermal properties

Low- and non-leucite-containing commercial porcelains with low firing temperatures have become popular. However, improving the strength of glass porcelains is difficult. The purpose of this study was to determine if dispersed glass particles could be used as a reinforcing agent for an all-glass porcelain. We produced 3 feldspathic glasses (high-fusing, medium-fusing, low-fusing) by melting powders consisting of potassium-feldspar and 0, 5, or 20 mass% Na2O, respectively. For high-fusing, medium-fusing, and low-fusing feldspathic glasses, the deformation temperatures were 945 degrees C, 647 degrees C, and 518 degrees C, and the thermal expansion coefficient values were 8.6 x 10(-6)/degrees C, 10.3 x 10(-6)/degrees C, and 13.4 x 10(-6)/degrees C between 25 degrees C and the glass-transition temperature, respectively. The high-fusing-glass (or medium-fusing-glass) powders were mixed with low-fusing-glass powders before being fired into test specimens. The mean flexural strength and fracture toughness (K1C) of 3 single-glass porcelains ranged from 57 to 63 MPa and from 0.68 to 0.73 MPa m(1/2), respectively, presenting no significant differences in one-way ANOVA. However, the flexural strength of 50% high-fusing-glass + 50% low-fusing-glass porcelain was 114 MPa (p < 0.05) and K1C was 1.2 MPa m(1/2) (p < 0.05). Microcracks were observed with a back-scattered scanning electron microscope and were associated with the high- (or medium-) fusing glass particles, suggesting residual stress in the low-fusing-glass matrix due to a coefficient of thermal expansion mismatch between the dispersed glass particles and the matrix glass. The dispersing glass particles appeared to act as a reinforcing agent for strengthening a glassy porcelain.


Material Design of Denture Base Resin Reinforced by Shape Memory Alloy Fiber

形状記憶合金繊維で強化した床用レジンの材料設計

We evaluated the tensile strength of denture base resin reinforced by shape memory alloy fiber. Fiber surface treatment with primer decreased the fiber-pull-out in a shape-memory-fiber reinforced denture base resin matrix composite and increased the tensile strength. We speculated that the increase in tensile strength was caused by an increase in interfacial strength between the fiber and the matrix. Since heat treatment at above 60℃ increased the composite tensile strength, this composite worked as a smartcomposite. Although there was no effect of heat treatment temperature on tensile strength, flexion of composite was observed after heat treatment at a higher temperature, suggesting that the heat treatment temperature should be lower. We speculated that the slight increase in tensile strength after heat treatment was caused by the higher martensite transformation starting temperature of the fiber.

形状記憶合金繊維で強化した床用レジンの引張強さについて検討した. 繊維表面のプライマー処理により形状記憶合金繊維強化レジン基複合材料の繊維のプルアウトが減少し, 引張強さが増加した. この引張強さの増加は繊維-マトリックス界面強度の増加によると考えられた. 60℃以上での熱処理によって複合材料の引張強さは若干増加したため, この試料がスマート複合材料として機能していることがわかった. 熱処理温度による引張強さの差は認められなかったが, 高温で熱処理した場合, 複合材料の屈曲が認められたため, 熱処理温度は低くすべきだとわかった. 熱処理後の引張強さがあまり増加しなかった理由は, 繊維マルテンサイト変態開始温度が高いためと考えられた.

The Journal of the Japanese Society for Dental Materials and Devices


形状記憶合金繊維強化床用レジンの損傷修復

形状記憶合金繊維強化床用レジンの損傷修復


Degradation and fracture of Ni-Ti superelastic wire in an oral cavity


Strengthening of glass-ionomer cement by compounding short fibres with CaO-P2O5-SiO2-Al2O3 glass.

The purpose of this study was to determine if short fibres of CaO-P2O5-SiO2-Al2O3 (CPSA) glass possessing a particular aspect ratio (length/diameter) could be used as a reinforcing agent for glass-ionomer cement. The powder of a commercial glass-ionomer cement (not resin modified) was mixed with variously sized CPSA glass short fibres before mixing with the liquid of the glass-ionomer cement. The mixed powders containing 60 mass% CPSA glass short fibres (diameter, 9.7 +/- 2.1 microm, aspect ratio, 5.0 +/- 0.9) obtained maximum values of 18 and 35 MPa for the diametral tensile strength (DTS) and flexural strength (FS) of set cements, respectively, after 24 h. These DTS and FS values were 1.8 and 4.5 times larger, respectively, than those of the set glass-ionomer cement not containing short fibres. Moreover, it was found that the addition of CPSA glass short fibres was remarkably more effective in the strengthening than electric glass (a typical glass fibre) short fibres. The results suggested that the CPSA glass short fibres acted as a reinforcing agent for strengthening the glass-ionomer cement, because of the shape of short fibres and reactivity between the mixing liquid and short fibres.


Fracture analysis of hydrogen-charged nickel-titanium super alloy


Acoustic emission and thermal expansion measurements for gypsum-bonded investment in casting flask during thermal processing

本論文は，石膏結合された埋没材および鋳型リングで拘束された同じ埋没材を用いて，加熱/冷却中のAEが計測され，AE活動度は250°Cと300°Cで高くなり，鋳型リングで拘束されれば更に活発になることが明らかになり，計算された熱応力の発生と鋳型リング拘束されたときの熱膨張率の変化とを比較した結果，AEの発生源は石膏の局部割れによるものであり，検出されたこれらの破壊は鋳型の精度を損ない歪みの原因になることを明らかにした．


Fracture toughness and durability of chemically or thermally tempered metal-ceramic porcelain

Thermocycling and water storage effects on fracture toughness (KIC) of chemically or thermally tempered metal-ceramic disks were investigated to evaluate the durability of tempering effects with regard to oral aqueous environment. Metal-ceramic disks (phi 10 mm x 2.0 mm) consisting of opaque porcelain (0.2 mm thick), body porcelain (1.3 mm) and Ni-Cr-Be alloy (0.5 mm) were prepared and the porcelain surfaces were polished with 1-micron diamond paste. The disks were subjected to ion exchange (potassium or rubidium) or thermal tempering treatments, then with the as-polished or further annealed disks, thermocycled for 8000, 15,000, and 22,000 cycles between 5 degrees C and 60 degrees C or stored in water at 37 degrees C for 33 days. After aging, KIC values of disks were determined by a Vickers indentation technique. Statistical analyses indicated that the KIC values of ion-exchanged and annealed disks were not significantly affected by the limited number of cycles and water storage, while the thermally tempered and untreated disks revealed a significant decrease in mean KIC from even 8000 cycles and after storage. However, there was no significant difference between thermocycling and water-storage effects on mean KIC of all surface treatment groups. Results indicate that chemical tempering (ion exchange) produced more durable residual stresses than does thermal tempering for metal-ceramic restorations. A low-thermal load only was unlikely to affect the apparent fracture toughness of porcelain.


Amount of metallic ions released from Ti-Ni alloy by abrasion in simulated bioliquids

The current density of Ti-56mass%Ni (Ti-50at.%) alloy after abrasion in simulated bioliquids was measured using a potentiostat to estimate the amount of metallic ions released from the alloy during repassivation and maturation. The current density in saline, saline with and without N2 bubbling, and Hanks' solutions with and without proteins after abrasion was measured and the amount of released ion was calculated from the integrated current density with time, assuming that Ti4+ and Ni2+ are equivalently released. No difference in the amount of released ion was observed between saline with and without N2 bubbling. Also, no difference was observed between saline and pH 7.4 Hanks' solution. More Ti4+ and Ni2+ were released in bioliquids with proteins than in saline with and without N2 bubbling (p < 0.05). That is, dissolved oxygen and inorganic ions in Hanks' solution did not influence the amount of released ion, but proteins influenced it. The release of metallic ions from metals and alloys in biological systems can be estimated by the methodology employed in this study.


Effects of added antibiotics on the basic properties of anti-washout-type fast-setting calcium phosphate cements

Journal of Biomedical Materials Research


Repassivation of titanium and surface oxide film regenerated in simulated bioliquid

The change in potential during repassivation of titanium in artificial bioliquids was examined, and the regenerated surface oxide film on titanium was characterized using X-ray photoelectron spectroscopy and Auger electron spectroscopy to elucidate the repassivation reaction of titanium in a biological system. The repassivation rate in Hanks' solution was slower than that in saline and was not influenced by the pH of the solution. This indicates that more titanium ions dissolve in a biological system than hitherto was predicted when the surface film is destroyed. Phosphate ions are taken up preferentially in the surface film during regeneration, and the film consists of titanium oxide and titanium oxyhydroxide containing titanium phosphate. Calcium ions and phosphate ions are adsorbed by the film after regeneration, and calcium phosphate or calcium titanium phosphate is formed at the outermost surface. Ions constituting Hanks' solution other than calcium and phosphate were absent from the surface oxide.


Mechanical properties of porcelain containing leucite ion exchanged with rubidium

The purpose of this study was to investigate the effectiveness of leucite crystals ion-exchanged with rubidium on the mechanical properties of glassy properties of glassy porcelain. For ion-exchange, a mixture of high-pure natural leucite (KAlSi_2O_6) powder and RbNO_3 were heat-treated at 450℃ (RLa) or 650℃ (RLb) for 1 four. The density of leucite increased as a result of the rubidium ion-exchange treatment. Polymorphic transformation temperatures of the ion-exchanged leucites were low compared with the unmodified leucite. Composite porcelains were prepared by blending each leucite (30 vol%) with "Component No.3" frit of Weinstein et al. patent. The flexural strength and fracture toughness of the glass-only and composite porcelains were measured by a three-point bending test and indentation technique. ANOVA and post hoc multiple comparisons test revealed that the flexural strength and fracture toughness of the composite porcelain containing RLa were signigicantly higher (p<.05 and p<.01, respectively) than those of the other groups. The results suggested that the rubidium-ion-exchanged leucite (RLa) could be a better reinforcing agent for dental porcelain.


Influence of the thermocycling in water on ion-exchanged porcelain


Acoustic emission signals from gypsum-bonded dental casting molds during thermal processing

To develop a suitable heating program for the investments which affect the casting accuracy/defects of prostheses, a probable microstructural change of the gypsum-bonded investments related to the transition of refractory particles during thermal processing was inspected by the measurement of acoustic emission (AE) signals. Gypsum-bonded cristobalite and quartz investment molds were used. AE measurements were carried out for the specimens in an electric furnace that was heated/cooled at a constant rate. For the heating process of the cristobalite investment, high AE activities were detected in the temperature range where the cristobalite was transformed. However, the AE signals detected were low for the second run of the heating and cooling processes. Even in the heating process, significant AE signals were not detected for the quartz investment. For cristobalite investment molds, micro-cracks are initiated and developed in relation to the transition of cristobalite particles in the mold. This leads to deterioration of the mechanical properties of the cristobalite investment at high temperatures (melt-pouring), and may affect the fitness of cast prostheses.

本論文は，石膏結合された埋没材の熱サイクル中の微視組織変化にAE法を適用して検討した結果，クリストバライト含有埋没材では，一回目の加熱中にその相変態に伴う温度域で活発なAE挙動を示したが，この埋没材中に微視クラックが発生し，クリストバライト埋没材の機械的性質を劣化させたため，二回目以降のAEは検出されなく，これによって，鋳型補綴の適合性に影響をおよぼすことを明らかにしている．


Estimation of residual stress in dental porcelain by Laser-Raman spectroscopy


Amount of hydroxyl radical on calcium-ion-implanted titanium and point of zero charge of constituent oxide of the surface-modified layer

To compare the surface properties of calcium-ion (Ca2+)-implanted titanium with those of titanium and to investigate the mechanism of bone conductivity of Ca2+-implanted titanium, amounts of hydroxyl radical of Ca2+-implanted titanium and titanium were estimated. Also, the point of zero charge (p.z.c.) of oxide constituting surface oxides of Ca2+-implanted titanium and titanium was determined. Results showed that the amount of active hydroxyl radical on Ca2+-implanted titanium was found to be significantly larger than that on titanium, indicating that the number of electric-charging sites of Ca2+-implanted titanium in electrolyte is more than that of titanium. The p.z.c. values of rutile (TiO2), anatase (TiO2), and perovskite (CaTiO3), were estimated to be 4.6, 5.9, and 8.1, respectively. Thus, Ca2+-implanted titanium surface is charged more positively in bioliquid than titanium, accelerating the adsorption of phosphate ions.

Journal of Materials Science. Materials in Medicine


Development of calcium phosphate cement for rapid crystallization to apatite


Surface modification of titanium in calcium-ion-containing solutions


Non-decay type fast-setting calcium phosphate cement: Hydroxyapatite putty containing an increased amount of sodium alginate


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.


Early bone formation around calcium-ion-implanted titanium inserted into rat tibia

Rat tibia tissue into which calcium ion (Ca2+)-implanted titanium was surgically placed was histologically analyzed to investigate the performance of the Ca(2+)-implanted titanium as a biomaterial. Calcium ions were implanted into only one side of titanium plates at 10(17) ions/cm2 and the Ca(2+)-treated titanium was surgically implanted into rat tibia for 2, 8, and 18 days. Tetracycline and calcein were used as hard-tissue labels. After excision of the tibia, the tissues were fixed, stained, embedded in polymethyl methacrylate, and sliced. The specimens were observed using a fluorescence microscope. A larger amount of new bone was formed on the Ca(2+)-treated side than on the untreated side, even at 2 days after surgery. In addition, part of the bone made contact with the Ca2(+)-treated surface. On the other hand, bone formation on the untreated side was delayed and the bone did not make contact with the surface. Mature bone with bone marrow formed in 8 days. Neither macrophage nor inflammatory cell infiltration was observed. The results indicated that Ca(2+)-implanted titanium is superior to titanium alone for bone conduction.

Journal of Biomedical Materials Research


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.


Blast coating method: New method of coating titanium surface with hydroxyapatite at room temperature


Microbial Properties of Titanium and Its Alloys for Oral Bacterium S. mutans

チタンおよびチタン合金の口腔内バクテリア S.mutans に対する細菌学的性質


Tissue response to fast-setting calcium phosphate cement in bone


Fluoridation of hydroxyapatite powder by ammonium hexafluosilicate


AES studies on dissolution of surface oxide from calcium-ion-implanted titanium in nitric acid and buffer solutions


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


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.


Micro-dissolution of calcium ions from calcium-ion-implanted titanium


Effect of ion-exchange on fracture toughness and physical strength of dental porcelains

焼付用陶材のイオン交換法による強化と破壊力学特性に関する研究

The Journal of the Japan Prosthodontic Society


Shock-absorbing Behavior of Soft Denture Liner --- Part 2 Influence of Lining Design on Shock Absorbability

軟質裏装材の衝撃緩衝に関する研究 --- 第2報 裏装法の違いが衝撃緩衝能に与える影響


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

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. 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). 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. 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.


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


Soft tissue response of calcium phosphate cements


Basic properties of hydroxyapatite putty made with fast-setting calcium phosphate cement and sodium alginate


Non-decay type fast-setting calcium phosphate cement using chitosan

Journal of Materials Science Materials in Medicine


Structure of surface-modified layers of calcium-ion-implanted Ti-6Al-4V and Ti-56Ni


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


Development of calcium phosphate based functional gradient bioceramics


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.

Journal of Biomedical Materials Research


Studies on Soft Denture Liner by using Viscoelastic Analysis --- Part 3. Effect of Viscosity of Soft Lining Materials on Stress Distribution in Denture Supporting Structures

粘弾性解析による軟質裏装材の有用性に関する研究 --- 第3報 軟質裏装材の粘性が床下組織の応力分布に及ぼす影響


In vivo setting behavior 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.


Thermal Diffusivity of Dental Ceramics at Room and Elevated Temperatures

歯科用セラミックスの熱拡散率の温度依存性について

The Journal of the Japanese Society for Dental Materials and Devices


Effects of fluoride on the calcium phosphate pricipitation method for dentinal tubules occlusion


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


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


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


Diffusion of elements in porcelain into titanium oxide


Studies on Soft Denture Liner by using Viscoelastic Analysis --- Part 2. Effect of Lining Method of Denture Liner on Stress Distribution in Supporting Structures

粘弾性解析による軟質裏装材の有用性に関する研究 --- 第2報 軟質裏装材の裏装法の違いが床下組織の応力分布に与える影響

The Journal of the Japan Prosthodontic Society


Effect of leucite crystals on the strength of glassy porcelain


Compatibility of MC3T3-E1 cells with calcium-ion-implanted titanium

カルシウムイオン注入チタンのMC3T3-E1細胞適合性


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


Acoustic emission measurements during order-disorder transformation and isothermal ordering process of Pd-Cu alloys

Pd-cu合金の規則一不規則変態，規則化過程のアコースティツク・エミツション


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


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

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


Properties of Castable Glass-ceramics Containing Cystalline Apatite and Magnesium Titanate

アパタイトとチタン酸マグネシウムを含有するキャスタブルセラミックスの諸性質


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


Shock-absorbing Behavior of Soft Denture Liner --- Part 1 Plate Specimens

軟質裏装材の衝撃緩衝に関する研究 --- 第1報 板状試料の衝撃緩衝能


Effect of soft denture liner on stress distribution in supporting structures under a denture

This study examined the effect of a soft denture liner on the distribution of stresses in the denture-supporting structures. Dentures without a linear and with three configurations of a soft liner were simulated by using a two-dimensional viscoelastic finite-element stress analysis. The stress intensity at functional force-bearing areas decreased when a soft denture liner was used. However, the stresses in the bone increased remarkably up to 3.0 seconds after loading. Because of the time-dependent effect of stresses applied to soft denture liners, denture patients who clench or brux may not benefit as greatly from soft denture liners. The study indicates that viscoelastic finite-element analysis is helpful for evaluating soft denture liners. Soft denture liners appear to be useful for improving the stress distribution in the supporting structures under dentures.

The International Journal of Prosthodontics


Studies on Soft Denture Liner by using Viscoelastic Analysis --- Part 1 Effect of Soft Denture Liner on Stress Distribution in Supporting Structures

粘弾性解析による軟質裏装材の有用性に関する研究 --- 第1報 軟質裏装材が床下組織の応力分布に及ぼす影響


Viscoelastic Analysis of the Supporting Structures under Denture --- Part 1 Effect of the Artificial Teeth Arrangment on the Stress Distributions in the Supporting Structures

粘弾性解析による義歯床下組織の応力分布 --- 第1報 人工歯の配列位置が義歯床下組織の応力分布に及ぼす影響


Effect of transient stress on acoustic emission behaviour during firing of dental porcelain

本論文は，歯科材料であるポーセレンの熱処理中のAE計測を行い，400∼600℃で発生するAEの発生源は，ガラス転移点以上におけるポーセレンに発生するトランジェント応力の緩和によることが，シミュレーション結果と良い対応を示していることから明らかにされたことを述べている．


Influence of tempering method on residual stress in dental porcelain

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


金属焼付陶材の加熱/冷却過程でのAE挙動

金属焼付陶材の加熱/冷却過程でのAE挙動

本論文は，陶材/合金積層板の加熱，冷却過程でのAE波の発生を測定し，加熱および冷却中に高温で発生するAEは，陶材の粘弾性変形量に依存しており，冷却中，低温で発生するAEは，合金板による陶材のせん断流れの拘束に依存していることが，シミュレーションにより明らかにされ，異種材料の接合過程で生ずる不適合応力の発生と緩和をAE法により動的に調べることができる可能性を述べている．

The Journal of the Japanese Society for Dental Materials and Devices


Evaluation of fracture toughness and residual stress in dental porcelain by indentation-microfracture method

微小圧子圧入破壊法による焼付用陶材の残留応力，破壊力学特性の評価

The indentation microfracture(IM)method was applied to estimate the fracture toughness and residual stress in the surface of dental porcelains which were slowly cooled and tempered by two different treatments.The shape parameter, m, in Weibull plots of the K_c's which were measured by IM method, was calculated to be 7.7 to 9.1 for the slow cooled specimen.Tempering had no significant effect on Weibull parameter.Factor of safety for the porcelain used for prosthesis was estimated to be 3.4 to 4.9 for the failure probability of 10^<-5>.Surface residual stress was estimated to be 26-28 and 64-88MPa(in compression)for the porcelain tempered in ambient air and forced air, respectively, from the median crack size after indentation.Estimated residual stress was in good agreement with the results of computer simulation by Asaoka et al.However, the residual stress could not be calculated for the porcelain with crystallization in its glass transition range during cooling because the reference sample was difficult to prepare.In concludsion, the fracture toughness and residual stress in micro-area(100∼400μm)of the dental baked-on porcelain prosthesis can be measured by the IM method.

徐冷, 空冷, 強制冷却した焼付用陶材表面の破壊靱性と残留応力を微小圧子圧入破壊(IM)法により調べた.IM法により測定された破壊靱性をWeibullプロットして, 形状母数を計算した結果は徐冷した陶材で, 7.7∼9.1であった.Temperingした陶材についても, ほぼ同じ値であった.形状母数から, 陶材使用にあたっての安全係数は危険率10^<-5>に対して3.4∼4.9と見積もられた.空冷, 強制冷却した陶材の表面残留応力は, median crackの長さから, 26∼28および64∼88MPaと計算された.この結果はAsaoka et al.のコンピュータシミュレーションによる残留応力の推定結果と良く一致した.しかし, ガラス転移温度域で冷却中に結晶化する陶材では, 残留応力をもたない参照試料の作製が困難なため, 残留応力は測定できなかった.以上の結果から, ここでの方法が陶材補綴物の微小部分の破壊靱性, 残留応力の測定に適用できる可能性と問題点が示された.


Temperature dependence of the coefficient of thermal expansion and viscosity of dental porcelains

陶材の熱膨張係数と粘度の温度依存性について

Temperature dependence of thermal coefficient of expansion was measured for six commercial body and opaque dental porcelains.The dependence of coefficient of thermal expansion on temperature in the glass transition range was over ten times higher than that of the glassy solid state of the porcelain during the heating process.The onset of the glass transition range and the temperature where the apparent coefficient of expansion reached the maximum value(determined from thermal deformation)were almost equal to the strain and the annealing points(defined by viscosity).The surface compressive residual stress for the 2mm thick porcelain slabs was simulated to be 16∼25 and 63∼92MPa, respectively, for the porcelain-cooled in air at ambient temperature and for that cooled with forced convection of compressed air from a temperature higher than the porcelain sag point.These findings suggested that the coefficient of thermal expansion in the glass transition range and viscoelastic behaviour of the porcelain are the major factors determining the residual stress in the porcelain-fused-to-metal(PEM)restorations, because the difference of the coefficient of thermal expansion between porcelain and alloy at the temperature where incompatible stress builds up was calculated to be much higher than 10×10^<-6>/℃.

市販焼付用陶材(歯冠色陶材とオペーク陶材)6種について熱膨張係数の温度依存性を調べた.昇温過程で測定された陶材の熱膨張係数はガラス転移温度域になると, それより低温に較べて10倍以上高い温度依存性を示すことが明らかにされた.熱膨張の測定からガラス転移温度域になる温度および最大の見かけの熱膨張係数を示す温度が粘度から計算されるひずみ点, 徐冷点とほぼ一致した.板厚2mmの各種平板陶材を焼成温度から放冷, 圧縮空気を吹き付けながら強制冷却したときに陶材表面に生じる圧縮の残留応力は16∼25, 63∼92MPaになることがシミュレーションにより推定された.また, 焼付用合金との接合において不適合応力が生じ始める温度域では, 陶材と合金の熱膨張係数の違いが10×10^<-6>/℃よりはるかに大きくなっており, 陶材のガラス転移温度域での熱膨張係数と粘弾性挙動が残留応力を決める重要な因子になっていることが明らかにされた.


Computer Simulation on Creep of Amalgam in Class I Cavity --- Occlusal Force was Loaded on Amalgam Filling

窩洞内でのアマルガムのクリープに関する有限要素法解析 --- 咬合接触がアマルガムにある場合


Computer simulation on creep of amalgam in class I cavity


Computer Simulation on Creep of Amalgam in Class I Cavity --- Occlusal Force was Loaded on Enamel

窩洞内でのアマルガムのクリープに関する有限要素法解析 --- 咬合接触が残存歯質にある場合


Transient and residual stress in porcelain/alloy strip for dental use as affected by tempering

Porcelain-fused-to-metal (PFM) restorations may develop cracks during processing or in-mouth service if the relative physico-mechanical properties of the porcelain and alloy are highly mismatched. The precise conditions when it might occur are not known. Many processing and property variations can affect the stresses developed throughout a porcelain-alloy system. To understand this, a computer simulation of stress in a PFM strip was conducted. The simulation considers cooling from temperatures higher than the porcelain sag point. The following temperature-dependent factors were incorporated : the elastic modulus, shear viscosity (porcelain), and coefficient of thermal expansion. Cooling rates during tempering of porcelain were measured. The cooling rate dependencies of the glass transition temperature and temperature distribution during cooling were also included in the simulation. The results suggest that tempering with a high cooling rate make up for compressive residual stress in body porcelain and the high curvature of the composite beam.

JSME International Journal. Series. 1, Solid Mechanics, Strength of Materials


Visco-elastic deformation of dental porcelain and porcelain -metal compatibility


Viscosity of dental porcelains in glass transition range

Changes in the viscosity of dental porcelain as a function of temperature are the controlling factor determining incompatible stresses in porcelain-fused-to-metal restorations. A new method was used to estimate viscosity using a viscoelastic analytical model that considers the relation between the heating rate and deformation temperature (Td) of dental porcelain with stress applied during heating. The activation energy of viscous flow and the viscous constant in the Arrhenius equation were calculated for six kinds of commercial body and opaque porcelains. The effect of the heating rate on the instantaneous coefficient of thermal expansion was also measured. Tg onset was graphically determined using data on thermal deformation and agreed well with the strain point as defined by viscosity. The data gathered in this study was also compared to the experimental results of previous works by others.


Temperature dependence of thermal expansion coefficient for palladium based binary alloy

Temperature dependencies of thermal expansion coefficients for the alloys of Pd-Ag, Pd-Cu and Pd-Co binary systems were measured at temperatures up to 900 degrees C, with heating and cooling rates of 5 degrees C/min. The coefficient of thermal expansion of alloys with no transformation in the temperature range of interest in porcelain firing was well approximated by a linear equation of temperature. The constants in the equation were shown as a function of the weight for the added element. Thermal expansion of the palladium-based alloy with no transformation was well estimated at any temperature range and at any composition by using the constants represented here. The coefficients of thermal expansion before and after order-disorder transformation and magnetic transformation were measured in Pd-Cu and Pd-Co alloys, respectively. The results suggest that transient and residual stresses in porcelain-fused-to-metal restorations can be effectively controlled by making use of transformation of the alloy.


Effect of viscoelastic deformation of soft tissue on stresses in the structures under complete denture


Finite Element Analysis on Physiological Mobility of Individual Teeth

有限要素法による歯の初期動揺に関する研究

The initial movement of the tooth was investigated by the finite element method.The mechanical properties of the periodontal membrane were estimated from the results of the simulation.The analysis was made by using an 8-point isoparametric finite element method.The upper central incisor with an axial directional load was simulated.The concept of the apparent elastic modulus was introduced to the stress-strain relation of the soft tissue, that is, soft tissue such as the periodontal membrane and the gingiva was considered to have stress dependent elastic moduli.At the first stage of the simulation, the stress and strain distributions in the paradentium were calculated by the conventional method.From the next stage, the apparent elastic moduli for the soft tissue were introduced to the calculation, that is, the elastic moduli for the soft tissue were computed from the calculated equivalent stresses of the previous stage.The calculations were repeated until the displacement values converged.The initial displacement of the tooth was not proportional to the applied load but showed a non-linear relationship.The relationship between load and displacement was approxiated by the n-th power equation.These results were in agreement with the clinical experimental results.The periodontal membrane is built up of different elastic moduli.The elastic moduli were low at the alveolar edge and the root apex.The equivalent stresses of the periodontal membrane were marked low in the alveolar edge and the root apex.In conclusion, the concept of the apparent elastic modulus is useful to investigate the initial movement of the tooth and estimate the mechanical properties of the periodontal membrane.

有限要素法を用いて歯の初期動揺を調べ, その結果から歯根膜の力学的性状の推定を行った.解析には, 8節点アイソパラメトリック要素よりなる軸対称体有限要素法を用いた.上顎中切歯の歯軸方向に荷重を負荷したときを想定した.軟組織の応力-歪関係に見掛けの弾性係数の考え方を導入した.すなわち, 歯根膜および歯肉のような軟組織が応力依存の弾性係数をもつと考えた.最初のステージでは, 歯周組織の応力-歪分布は従来の方法で計算した.次のステージから, 計算に軟組織の見掛けの弾性係数を導入した.すなわち, 軟組織の見掛けの弾性係数を, 前ステージで計算された相当応力をもとに求めた.計算は, 変位量が収束するまで繰り返した.次のような結論を得た.1.歯の初期変位量は, 負荷荷重に対して比例関係でなくn乗式で近似される非線形な関係を示し, 在来の臨床的実験結果と一致した.2.歯根膜は, 部位により異なった弾性係数をもつと考えられることが明らかになった.また, 弾性係数は歯槽縁および根尖部で低くなった.3.歯根膜の相当応力は, 歯槽縁および根尖部で顕著に低くなった.以上より, 見掛けの弾性係数の考え方が歯の初期動揺を調べ, 歯根膜の力学的性状を推定するために有用であると考えられた.

The Journal of the Japanese Society for Dental Materials and Devices


Transient and residual stress in a porcelain-metal strip

Porcelain-fused-to-metal (PFM) restorations may develop cracks during processing or in-mouth service if the relative physico-mechanical properties of the porcelain and metal are highly mismatched. Precise conditions when this might occur are not known. Many processing and property variations can affect the stresses developed throughout a porcelain-metal system. To understand this, we conducted a computer simulation of stress developed in a PFM beam. The simulation considers cooling from temperatures higher than the porcelain sagpoint. The following temperature-dependent factors were incorporated: the elastic modulus, shear viscosity (porcelain), and coefficients of thermal expansion. The cooling rate dependencies of the glass transition temperature, (Tg), and the temperature distribution during cooling were also included. The results suggest that transient tensile stress at the porcelain alloy interface may result in cracks in the porcelain during cooling. Occlusal forces may set up stresses to cause cracking at the surface of the porcelain if the compressive residual stress is not high enough. PFM restorations with an alloy of high thermal expansion coefficient require rapid cooling; on the contrary, PFM restorations with the alloys of lower coefficients require slow cooling. A high cooling rate can make up for thermal expansion mismatches between the alloy and the porcelain up to 2 x 10(-6)/degrees C. Finally, the results indicated that curvature was not a sensitive indication of stress for a multimaterial beam when visco-elastic relaxation and high cooling rates are involved. For the case modeled here, curvature varied inversely with a 1/2 to 1/7th power of the stress.


Transient and residual stresses in dental porcelain as affected by cooling rates

The development of either transient or residual stress in a slab of dental porcelain during cooling was simulated by use of a super-computer. The temperature dependences of the elastic modulus, the thermal expansion coefficient, and the shear viscosity, and the cooling rate dependence of the glass transition temperature, Tg, were considered in this calculation. Internal stress and viscoelastic creep were computed for several cooling rates. Calculated results display stress profiles which agree reasonably well with reported measured profiles in quenched, tempered glasses. The calculated residual surface stress, sigma, could be fit by the following empirical formula, sigma = kl2(q/q0)n, q is the cooling rate, q0 is a reference cooling rate and l is the half-thickness of the porcelain. The method by which residual stress develops is also discussed. This discussion suggests a method for strengthening of the porcelain by the development of high-compressive residual stress on the surface.


Estimation of residual stress in porcelain alloy system by thermal shock test


Mechanical properties and biomechanical compatibility of porous titanium for dental implants

Titanium powder with a granule diameter of 420-500 micron was prepared and porous titanium specimens were made from this powder. The mechanical properties of these specimens were examined. The compressive strength and low cyclic compressive fatigue strength were 182 and 40 MPa, respectively. Fractography was also observed by scanning electron microscopy. Typical fatigue characteristics of the bonding areas of the powder were observed. In addition, porous-titanium-coated dental implants with pure titanium cores were prepared. The compressive strength of the material used was 230 MPa, fatigue strength not being improved. Biomechanical stress calculations using the finite element method were made using a model that employed the use of the material implanted in alveolar bone. Shear stress at the implant-bone interface as well as compressive stress concentrations in the bone was calculated. The most suitable elastic modulus for the dental implant was then estimated from these calculations. Finally, based on these results, the use of porous titanium for dental implants was assessed.

Journal of Biomedical Materials Research


Evaluation of thermal residual stress after firing of porcelain/alloy veneer


Correlation between microstructure of Ag-Pd-Au-Cu alloy and changes in shape on aging

An investigation has been carried out to study changes in shape on aging in plastic deformed Ag-Pd-Au-Cu alloys. The changes in shape were measured in order to establish a relationship to the aging heat treatments. Their microstructure was observed in order to clarify this phenomenon at the same time. They were also investigated quantitatively using a feature analysis system. The changes in shape were interpreted as the shrinkage in volume resulting from the formation of the ordered phase. They were smaller at aging temperatures below 673 K. The change in microstructure was different at aging temperature between 573 and 773 K. These phenomena were due to the following: First, nodules which nucleated at the grain boundaries would have grown into the grains well before the formation of the ordered phase, and second, the shrinkage in volume would have been of a different kind that the ordered phase. Therefore aging treatments should be carried out at low temperature in order to minimize the changes in shape. Also, nodular growth should be inhibited in order to maximize the hardening in Ag-rich alloys.


Studies on Sintering of Dental Porcelain : (Part 4)Strength and Transluency of Sintered Composite

陶材の焼結に関する研究.第4報複合焼結体の強さと透光性について

The sintered composite were made from mixed powder compacts prepared from low fusing glass powders and each one of alumina powder, quartz powder, silica glass powder using sintering method at the temperature to 1000℃, and the affections of physical properties of sintered composite were investigated by measurements of transverse strength and transparency.Transverse strength value of sintered composite of alumina and pyrex glass(expansion coefficient 3.6×10^<-6>)or soda-lime-silica glass(10.7×10^<-6>)increased with increase alumina content, particularly sintered composite with 50wt% alumina addition showed the transverse strength value of 170-180MPa.The addition of alumina was more effective on the strength of sintered composite comparing with quartz and silica glass, inversely, transparency of sintered composite decreased with increase of alumina content.In the case of the sintered composite of silica glass and low fusing glass, transverse strength velue decreased with increase of silica glass content.The sintered composite with silica glass addition showed smaller transparency value by difference of the refractive index due to the generation of cristobalite followed with the crystallization of cristobalite than that without crystallizing property.

本研究では低融ガラス粉末にアルミナ, 石英および石英ガラス粉末を配合した焼成温度範囲の広い複合焼結体の強さと透光性について調べた.アルミナを加えた複合焼結体の曲げ強さはガラス成分や膨張係数の相違にかかわらずアルミナの含有量が増加するにつれて大きくなった.しかもアルミナを50wt%含む複合焼結体はガラス単独の焼結体の2∼3倍以上の170∼180MPaの曲げ強さを示したが, 透光性はアルミナを20%加えただけでも急激に低下した.石英を添加した場合は強さの向上がわずかであり, 石英ガラスではかえって強さが低下する傾向がみられた.中でも膨張係数の大きい低融ガラスとの複合焼結体が極端な強さの低下を示したが, 膨張係数が比較的大きくてもクリストバライトを析出しない場合はかなり石英ガラスを加えても強さがほとんど低下しないことがわかった.またクリストバライトを析出しない低融ガラスと石英ガラスの複合焼結体はとくに高い透光性を示した.


Studies on the Mechanical Properties of a Metal-Ceramic Restoration : (Part 2)Residual Stress and Deformation during Cooling Down --- 第2報焼成後の残留応力と変形について

金属焼付陶材の機械的性質に関する研究 --- 第2報焼成後の残留応力と変形について

Residual stress and deformation of the porcelain fused to metal restoration were calculated by the theory of statically indeterminate beam and the finite element method.Physical and mechanical properties of the materials were supposed not to change from the softening temperature of ceramic to the room temperature.The effect of the thermal expansion coefficient, the elastic modulus of metal, the softening temperature of ceramic, and the thickness ratio of metal to ceramic were calculated.The following results were obtained.(1)Theory of statically indeterminate beam was good agreement with the finite element analysis.(2)From the calculation on the effect of the thermal expansion coefficient, the residual stress and the deformation were directly in proportion to the difference in thermal expansion coefficients of metal and ceramic.(3)If the metal had low elastic modulus, so the residual stress in ceramic was low, and the deformation of the sintered porcelain veneer was small.But the elastic modulus had smaller effect on the internal stress and the deformation than the thermal expansion coefficient.(4)If the softening temperature of ceramic droped, so internal stress decreased.But the softening temperature had only smaller effect.(5)If the thickness of the metal took under 20% of the sintered porcelain veneer, residual stress in ceramic was low.But over 80%, the stress rapidly increased.If the metal thickness took from 20% to 80% the stress at the interface had nearly constant value.So, the change of metal thickness for this range is not effecrtive for the arrest of the interface fracture.

金属焼付陶材中の残留応力と変形を非静定梁の理論と有限要素法によって計算した.材料の物理的, 機械的性質は陶材の軟化温度から室温まで変化しないものと仮定した.熱膨張係数, 金属の弾性率, 陶材の軟化温度, 金属と陶材の板厚比の影響について調べた.次の結論が得られた.1)不静定梁の理論は有限要素法と良く一致した.2)熱膨張係数の影響に関する計算から, 残留応力と変形は金属と陶材の熱膨張係数の差に直接比例していた.3)金属の弾性係数が低ければ, 陶材中の残留応力は小さい.そして, 金属焼付陶材の変形も小さい.しかし, 弾性係数は熱膨張係数に較べて, 内部応力と変形にあまり影響を及ぼさない.4)陶材の軟化温度が低下すると内部応力は小さくなる.しかし, 軟化温度の影響も小さい.5)金属の板厚が金属焼付陶材の20%以下ならば, 陶材中の残留応力は小さい.しかし, 80%以上になると急激に増大する.金属の厚さが20%から80%の間ならば, 界面での応力はほぼ一定である.したがって, 金属の厚さをこの範囲で変化させても界面破壊の防止には有効でない.


金銀パラジウム合金の機械的性質に関する研究 --- 第1報時効硬化熱処理と引張変形挙動との関係


金属焼付陶材の機械的性質に関する検討 --- 第1報引抜試験について

金属焼付陶材の機械的性質に関する検討 --- 第1報引抜試験について

Journal of the Japan Society for Dental Apparatus and Materials


複合2相合金の機械的性質に関する有限要素シミュレーション

複合2相合金の機械的性質に関する有限要素シミュレーション


2相合金における引張変形挙動と破壊の起源について

2相合金における引張変形挙動と破壊の起源について


有限要素法によるOFF AXIS短繊維強化合金の引張強度に関する研究

有限要素法によるOFF AXIS短繊維強化合金の引張強度に関する研究


延性破壊におけるvoidの起源と成長に関するシミュレーション

延性破壊におけるvoidの起源と成長に関するシミュレーション


粒子を含む複相合金の引張挙動に関するシミュレーション

粒子を含む複相合金の引張挙動に関するシミュレーション


繊維型第2相を含む複相合金の引張挙動に関するシミュレーション

繊維型第2相を含む複相合金の引張挙動に関するシミュレーション


Effect of surface oxide films on degradation of titanium


Effects of fiber-resin interface property on shape recovery and mechanical properties of denture-base-resin matrix smart composite


Porous titanium compacts as biomaterials for hard tissue replacement

Porous Metals and Metal Foaming Technology (JIMIC=4)


Porous titanium compacts as advanced medical device

Cellular Metals for Structural and Functional Applications


Modeling simulation of graded function in biomaterials

数値計算力学によるバイオマテリアルの傾斜機能の評価

Proceedings of the 15th Symposium on Functionally Graded Materials


Shape recovery of Ni-Ti alloy fiber-reinforced denture base resin by smart repair process


Evaluation of bioceramics containing a-tricalcium phosphate


Sintered porous titanium and titanium alloys as advanced biomaterials


Compositions of surface oxide films on titanium alloys regenerated in Hanks' solution

The Fourth Pacific Rim International Conference on Advanced Materials and Processing (PRICM4)


Sintered titanium compacts with biological function as biomaterials for hard tissue replacement


Influences of crystal phases on bioactivity of calcium phosphate cements


Development of Ca ion implanted titanium and its alloys for medical and dental applications


Calcium phosphate precipitation on titanium and surface-modified titanium


Soft tissue responses of calcium phosphate cements


Basic properties of hydroxyapatite putty made with fast-setting calcium phosphate cement and sodium alginate


Approaches for bone-replacing calcium phosphate cement --- Effect of NaHCO3 addition on the properties of calcium phosphate cement


Surface characterization of Ca2+ implanted titanium for biomaterials


Calcium phosphate precipitation or titanium in electrolyte and its acceleration by calcium-ion implantation


Evaluation of fracture toughness and residual stress in dental porcelain by indentation-microfracture method

Proceedings of the 4th International Conference on Residual Stress (ICRS IV)


Thermal conduction of dental metal-ceramic composite at room and elevated temperatures and its compatibility

Proceedings of 1st International Conference on Composite Engineering (ICCE/1)


Acoustic emission behavior during heating/cooling of Pd-Cu alloys

Proceedings of the 11th International Acoustic Emission Symposium


Propeties and interactions of oral structures and restorative materials --- Part 3 Dental alloys, ceramics and metrology and analyses


Effect of transformation of alloy on transient and residual stresses in a porcelain-metal strip

Residual Stress-III: Science and Technology


Residual stress in a porcelain-metal strip related to thermo-physical properties of materials


Marginal fracture mechanism of amalgam filling in the class I cavity

Proceedings of 7th International Conference on Biomedical Engineering


陶材/合金補綴物の焼成条件と残留応力の関係

陶材/合金補綴物の焼成条件と残留応力の関係

日本機械学会講演論文集 E

日本機械学会講演論文集 E


Properties and intercations of oral structures and restorative materials --- Part 3 Dental alloys, ceramics and metrology


異種材料接合 --- 穴と温度の関係

異種材料接合 --- 穴と温度の関係


Properties and interactions of oral structures and restorative materials --- Part 3 Dental alloys, ceramics and metrology


コンピュータで風冷強化の原理を見る

コンピュータで風冷強化の原理を見る


硬組織代替用材料の生体力学的な適合性に関する研究

硬組織代替用材料の生体力学的な適合性に関する研究


チタン合金およびジルコニウム合金の医歯学的応用 --- 多孔性材料の強度と破壊について

バイオマテリアル学会大会論文集

バイオマテリアル学会大会論文集


チタン合金およびジルコニウム合金の医歯学的応用 --- 多孔性生体材料の応力解析について

バイオマテリアル学会大会論文集

バイオマテリアル学会大会論文集


歯科用Ag-Pd-Cu系合金の時効硬化に及ぼす冷間加工の影響

歯科用Ag-Pd-Cu系合金の時効硬化に及ぼす冷間加工の影響

バイオマテリアル学会大会論文集

バイオマテリアル学会大会論文集


複合2相合金の組織と引張変形挙動に関する研究

複合2相合金の組織と引張変形挙動に関する研究


2相合金の変形，破壊挙動

2相合金の変形，破壊挙動


計算機シミュレーション法の歯科への応用

計算機シミュレーション法の歯科への応用