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Titanium-silver (Ti-Ag) alloy has been improved for machinability and mechanical properties, but its anti-biofilm properties have not been elucidated yet. Thus, this study aimed to evaluate the effects of Ti-Ag alloy on biofilm formation and bacterial viability in comparison with pure Ti, pure Ag and silver-palladium (Ag-Pd) alloy. Biofilm formation on the metal plates was evaluated by growing Streptococcus mutans and Streptococcus sobrinus in the presence of metal plates. Bactericidal activity was evaluated using a film contact method. There were no significant differences in biofilm formation between pure Ti, pure Ag and Ag-Pd alloy, while biofilm amounts on Ti-20% Ag and Ti-25% Ag alloys were significantly lower (p

The purpose of this study was to evaluate the corrosion resistance of experimental dental Ti-Ag alloys in 0.9% NaCl solution. Open-circuit potential (OCP) measurement and elution tests of the alloys with 5–30% Ag were performed. The amounts of both Ti and Ag ions released from the alloys with Ag � 20% were below the detection limit. A very small amount of Ti ions was released from some of the 22.5% Ag specimens and some of the 25% Ag specimens. The time for the Ti-Ag alloys with 5–25% Ag to become the stable potential was earlier than that for titanium, and the OCP of the alloys was higher than that of titanium. These results indicated that the corrosion resistance of the alloys with 5– 25% Ag was equivalent to that of titanium. On the other hand, it was suggested that the precipitation of TiAg deteriorated the corrosion resistance of Ti-Ag alloys because TiAg dissolved preferentially in the NaCl solution. Ti-Ag alloys with 5–25% Ag can be used not only as dental restorative materials but also as dental implant materials. [doi:10.2320/matertrans.M2009355]

The purpose of this study was to improve the grindability of titanium by alloying with zirconium. The grindability of dental cast Ti-Zr alloys (10, 20, 30, 40 and 50 mass% Zr) was evaluated using a carborundum wheel. The Ti-Zr alloys up to 30 mass% Zr formed an α structure, and the 40 mass% Zr and 50 mass% Zr alloys formed an α′ structure. The Ti-40 mass% Zr alloy at up to 1000 m/min and the Ti-50 mass% Zr alloy at up to 1250 m/min exhibited significantly higher grindability than titanium. More than twice the volume of metal was removed from the alloys than from titanium per minute. The improved grindability could be attributed to the α′ structure in addition to the decrease in elongation. The Ti-Zr alloys, which formed an α′ phase structure, are candidates for use as machinable biomaterial in dental applications.

This study is an investigation of the machinability of experimental Ti-Cu alloys (2, 5, and 10 mass% Cu) as new dental titanium alloy candidates for CAD/CAM use. The alloys were slotted with a vertical milling machine and carbide square end mills under two cutting conditions. Their machinability was evaluated through cutting force using a three-component force transducer fixed on the table of the milling machine. The horizontal cutting forces of the Ti-Cu alloys tended to increase as the concentration of copper increased. The feed force for Ti-10%Cu was more than twice as large as that for titanium under both cutting conditions. Alloying with copper reduced the machinability of titanium under the present cutting conditions. The adverse effect on the cutting force was attributed to the higher degree of tensile strength and hardness of the Ti-Cu alloys than of titanium.

This study was an examination of the galvanic corrosion of ferritic stainless steels, namely SUS 444, SUS XM27, and SUS 447J1, in contact with a Fe-Pt magnet. The surface area ratio of each stainless steel to the Fe-Pt magnet was set at 1/1 or 1/10. Galvanic corrosion between the stainless steels and the magnet was evaluated by the amount of released ions and the electrochemical properties in 0.9% NaCl solution. Although each stainless steel showed sufficient corrosion resistance for clinical use, the amount of ions released from each tended to increase when the stainless steel was in contact with the magnet. When the surface area ratio was reduced to 1/10, the amount of Fe ions released from the stainless steels increased significantly more than when there was no contact. Since contact with the magnet which possessed an extremely noble potential created a very corrosive environment for the stainless steels, 447J1 was thus the recommended choice against a corrosion exposure as such.

This study investigated the machinability of experimental Ti-Ag alloys (5, 10, 20, and 30 mass% Ag) as a new dental titanium alloy candidate for CAD/CAM use. The alloys were slotted with a vertical milling machine and carbide square end mills under two cutting conditions. Machinability was evaluated through cutting force using a three-component force transducer fixed on the table of the milling machine. The horizontal cutting force of the Ti-Ag alloys tended to decrease as the concentration of silver increased. Values of the component of the horizontal cutting force perpendicular to the feed direction for Ti-20% Ag and Ti-30% Ag were more than 20% lower than those for titanium under both cutting conditions. Alloying with silver significantly improved the machinability of titanium in terms of cutting force under the present cutting conditions.

Objectives The purpose of this study was to evaluate the fit of metal ceramic crowns cast in Au-1.6 wt% Ti alloy and investigate the effect of abutment finish line curvature on the fit of crowns. Methods Three types of finish line curvature abutments were prepared (1, 3 and 5mm-curvature). For each type of abutment, five metal ceramic crowns of the facial veneered type were fabricated, which were cast in Au-1.6 wt% Ti alloy. Used as controls, another fifteen specimens were made from a commercially available gold alloy. The fit was measured in the as-cast and after porcelain application. Results In the as-cast specimens, the greater the finish line curvature was, the larger the gaps exhibited at the mesial and distal margins of copings, compared with labial and lingual margins. The distal margin of copings for 5mm-curvature abutments showed the largest gap (35 (7) microm). After porcelain application, the greater was the finish line curvature, the larger the labial marginal gap became (mean 44, 34, 25 microm, respectively, for 5, 3, 1mm-curvature). However, there was no significant difference on marginal gaps between specimens of Au-1.6 wt% Ti alloy and control gold alloy. Significance This study indicated that the metal ceramic crowns cast in Au-1.6 wt% Ti alloy had equivalent accuracy to those that cast in control gold alloy, and the abutment finish line curvature had a significant effect on the marginal fit of metal ceramic crowns.

The age-hardening behaviour, phase transformation and related microstructural changes of an experimental Ag–Cu–Pd–Au alloy were examined by means of hardness test, X-ray diffraction (XRD), scanning electron microscopic (SEM) observations and electron probe microanalysis (EPMA). The specimen alloy showed apparent age-hardenability at the aging temperatures of 350 °C and 400 °C. By aging the solution-treated specimen at 400 °C, two phases of the Ag-rich α1 phase and the Pd-containing Cu-rich α2 phase were transformed into four phases of the Ag-rich α 1 ′ phase, the Cu-rich α 2 ′ phase, the CsCl-type CuPd phase and the AuCu(I) ordered phase. Microstructure of the solution-treated specimen consisted of the Ag-rich α1 matrix, Cu-rich α2 particle-like structures of various sizes and the lamellar structure of the α1 and α2 phases. When the peak hardness was obtained, the very fine lamellar structure consisting of the Ag-rich α 1 ′ and Cu-rich α 2 ′ phases was newly formed in the matrix. By further aging, the very fine lamellar structure grew and coarsened apparently, and the matrix was covered with the coarsened lamellar structure. The hardness increase was considered to be caused mainly by the diffusion and precipitation of Cu from the Ag-rich α1 matrix, and the hardness decrease in the latter stage of age-hardening process was caused by the coarsening of the very fine lamellar structure. The CsCl-type CuPd phase and the AuCu(I) ordered phase did not contribute to the hardness increase.

As part of our systematic studies characterizing the properties of titanium alloys, we investigated the grindability of a series of cast Ti-Hf alloys. Alloy buttons with hafnium concentrations up to 40 mass% were made using an argon-arc melting furnace. Each button was cast into a magnesia-based mold using a dental titanium casting machine; three specimens were made for each metal. Prior to testing, the hardened surface layer was removed. The specimens were ground at five different speeds for 1 min at 0.98 N using a carborundum wheel on an electric dental handpiece. Grindability was evaluated as the volume of metal removed per minute (grinding rate) and the volume ratio of metal removed compared to the wheel material lost (grinding ratio). The data were analyzed using ANOVA. A trend of increasing grindability was found with increasing amounts of hafnium, although there was no statistical difference in the grindability with increasing hafnium contents. We also found that hafnium may be used to harden or strengthen titanium without deteriorating the grindability.

Anodic polarization tests were performed in 0.9% NaCl and 1% lactic acid solutions to characterize the relationship between the corrosion behavior and the microstructures of cast Ti-Ag (5-40% Ag) alloys. The anodic polarization curves for the Ti-Ag alloys up to 17.5% Ag were similar to those for pure titanium in both solutions. On the other hand, an abrupt increase in the current density was observed for the alloys with more than 20% Ag in the NaCl solution and with more than 27.5% Ag in the lactic acid solution. The microstructures of the corroded alloy surfaces indicated the deterioration of precipitated intermetallic compounds along the grain boundaries. The Ti-Ag alloys up to 17.5% Ag had excellent corrosion resistance similar to that of pure titanium. The alloys with 20-25% Ag may be also used as dental alloys, since they passivated again immediately after preferential dissolution in the NaCl solution.

This study examined the characteristics of as-cast Ti-Cr(7–19%)-Cu(3–7%) (all percentages in this article are mass%) alloys to evaluate their suitability for dental applications; studies on the alloy structures and mechanical properties, grindability, and corrosion behavior were included in the investigation. The alloys were centrifugally cast and bench-cooled in investment molds. The x-ray diffractometry of the as-cast alloys bench-cooled in the molds indicated the following phases: α+β+ω in the 7% Cr and 7% Cr+3% Cu; β+ω in the 13%Cr; and β in the 13%Cr+3% Cu through the 19%Cr+3% Cu alloys. The strengths of the binary β Ti-Cr and ternary β Ti-Cr-Cu alloys with 13 and 19% Cr were approximately two times higher than those of CP Ti. The alloy ductility was dependent on the chemical composition and thus, the microstructure. The 7% Cr alloys were extremely brittle and hard due to the ω phase, but the ductility was restored in the 13 and 19% Cr alloys. The hardness (HV) of the cast 13 and 19% Cr alloys was approximately 300–350 compared with a value of 200 for CP Ti. The grindability of the cast alloys was examined using a rotating SiC wheel at speeds (circumferential) of 500 and 1250 m/min. At the higher speed, the grindability of the 13 and 19% Cr alloys increased with the Cu content. The grindability of the 13% Cr alloy with 7% Cu was similar to that of CP Ti. Evaluation of the corrosion behavior in an artificial saliva revealed that the alloys are like many other titanium alloys within the normal intraoral oxidation potential. The wear resistance testing of these alloys also showed favorable results.

This study characterized the electrochemical behavior of Ti-Hf binary alloys in a simulated oral environment. Ti-Hf alloys (10, 20, 25, 30, 35 and 40 mass% Hf) were prepared by arc-melting titanium sponge and hafnium sponge. Specimens of each alloy (n = 4) were prepared using a dental titanium casting system with a MgO-based investment. Specimens were inspected with X-ray radiography to ensure minimal internal porosity. Castings (n = 4) made from pure titanium and commercially pure titanium were used as controls. The ground flat surface (10 mm x 10 mm) on each specimen where approximately 30 microm was removed was used for the characterization. Sixteen-hour open-circuit potential (OCP) measurement, linear polarization and potentiodynamic cathodic polarization were performed sequentially in aerated (air + 10% CO2) MTZ synthetic saliva at 37 degrees C. Potentiodynamic anodic polarization was conducted in the same medium but deaerated (N2 + 10% CO2) 2 h before and during testing. Polarization resistance (R(P)) and Tafel slopes were determined, as were corrosion current density (I(CORR)) and passive current density (I(PASS)). Results were subjected to nonparametric statistical analysis (alpha = 0.05). The OCP stabilized (mean values -229 mV to -470 mV vs. SCE) for all specimens after the 16-h immersion. Similar passivation was observed for all the metals on their anodic polarization diagrams. The Kruskal-Wallis test showed significant differences in OCP among the test groups (p = 0.006). No significant differences were found in R(P), I(CORR) or I(PASS) among all the metals (p>0.3). Results indicate that the electrochemical behavior of the Ti-Hf alloys examined resembles that of pure titanium.

The aim of this investigation was to evaluate the metal-ceramic bonding of Au-1.6 wt% Ti alloy. Therefore, the coefficient of thermal expansion, modulus of elasticity, ceramic bonding strength, and hardness of Au-1.6 wt% Ti alloy were measured. The metal-ceramic interface was observed by EPMA to investigate its bonding mechanism. The Au-1.6 wt% Ti alloy showed a coefficient of thermal expansion close to that of conventional precious metal alloys for metal-ceramics. Bonding strength was 25 MPa or higher for all specimens--whether ceramic-fired directly after casting, or following oxidation treatment or age hardening. Specimens subjected to oxidation treatment showed slightly lower post-firing hardness than those age-hardened. EPMA observation showed an accumulation of Ti and O contents on the alloy side at the metal-ceramic interface.

In this study, the grindability of cast magnetic alloys (Fe-Pt-Nb magnetic alloy and magnetic stainless steel) was evaluated and compared with that of conventional dental casting alloys (Ag-Pd-Au alloy, Type 4 gold alloy, and cobalt-chromium alloy). Grindability was evaluated in terms of grinding rate (i.e., volume of metal removed per minute) and grinding ratio (i.e., volume ratio of metal removed compared to wheel material lost). Solution treated Fe-Pt-Nb magnetic alloy had a significantly higher grinding rate than the aged one at a grinding speed of 750-1500 m x min(-1). At 500 m x min(-1), there were no significant differences in grinding rate between solution treated and aged Fe-Pt-Nb magnetic alloys. At a lower speed of 500 m x min(-1) or 750 m x min(-1), it was found that the grinding rates of aged Fe-Pt-Nb magnetic alloy and stainless steel were higher than those of conventional casting alloys.

This study investigated the effect of heat history on the corrosion of keepers used for dental magnetic attachments. Ferritic stainless steels of SUS 444 and 447J1 were prepared with heat treatments in the temperature range of 550-850 degrees C for 1-5 hours. The stainless steels were electrochemically and metallurgically examined by anodic polarization curves in a 0.9% NaCl solution and by microstructural observation using an electron probe microanalyzer with WDS. Heating both kinds of stainless steel at 650-750 degrees C for two hours or more led to the deterioration of their corrosion resistance. For example, there was evidence of a reduction in the breakdown potentials and an increase in the current densities of the anodic polarization curves. These phenomena were attributed mainly to the precipitation of the sigma (FeCr) or chi (Fe18Cr6Mo5) phase, which sometimes resulted in intergranular corrosion. When dental alloys are cast in investment molds embedding the keepers, the heat time required for thermal expansion of the molds should be kept under one hour.

A series of binary Ti-Cu alloys containing 5-20 mass% Cu was prepared, and the corrosion behavior of alpha-Ti and Ti2Cu composing the Ti-Cu alloys were examined based on the anodic polarization curves and released ions in 0.9% NaCl and 1% lactic acid solutions. In both solutions, the Ti-Cu alloys showed the same anodic polarization curves as titanium in the condition below 1.4 V. However, precipitation of Ti2Cu contributed to a small increase in current densitiy in the transpassive region beyond 1.4 V. The amount of Cu ions released from Ti2Cu was 0.260 and 1.003 (microg/cm2/7 days) in 0.9% NaCl and 1% lactic acid solutions respectively. Although these values were larger than those from alpha-Ti (0.0379 +/- 0.0041 and 0.0962 +/- 0.0327 (microg/cm2/7days) in NaCl and lactic acid solutions respectively), they were not greater than those from type 4 gold alloy under the same conditions.

In the present study, the machinability of titanium, Ti-6Al-4V, Ti-6A1-7Nb, and free-cutting brass was evaluated using a milling machine. The metals were slotted with square end mills under four cutting conditions. The cutting force and the rotational speed of the spindle were measured. The cutting forces for Ti-6Al-4V and Ti-6Al-7Nb were higher and that for brass was lower than that for titanium. The rotational speed of the spindle was barely affected by cutting. The cross sections of the Ti-6Al-4V and Ti-6Al-7Nb chips were more clearly serrated than those of titanium, which is an indication of difficult-to-cut metals. There was no marked difference in the surface roughness of the cut surfaces among the metals. Cutting force and the appearance of the metal chips were found to be useful as indices of machinability and will aid in the development of new alloys for dental CAD/CAM and the selection of suitable machining conditions.

Anodic polarization was performed in 0.9% NaCl and 1% lactic acid solutions to characterize the relationship between the corrosion behavior and microstructures of cast Ti-Au (5-40%) alloys. An abrupt increase in the current density occurred at approximately 0.6 V vs. SCE for the 30% and 40% Au alloys in the 0.9% NaCl solution. The microstructures after corrosion testing indicated that this breakdown may have been caused by the preferential dissolution of the Ti3Au. However, the potential for preferential dissolution was higher than the breakdown potential of stainless steel or Co-Cr alloy, which meant that the corrosion resistance of the Ti-Au alloys was superior. In 1% lactic acid solution, the corrosion resistance of the Ti-Au alloys was excellent, with no breakdown at any composition. In the present test solutions, the Ti-Au alloys up to 20% Au had good corrosion resistance comparable to that for pure titanium.

In this study, wedge-shaped CP titanium castings and Ti-6Al-7Nb alloy castings were produced by three types of investment. The effects of the castings' thickness on surface reaction layer were investigated by measuring Vickers hardness, observing the microstructure, and analyzing the oxygen concentration. It was found that the thickness of the surface reaction layer was affected by the thickness of the wedge-shaped castings, and that the hardness value near the surface became lower toward the tip of the wedge-shaped CP titanium and Ti-6Al-7Nb alloy castings. The surface reaction layer of the Ti-6Al-7Nb alloy castings was thinner than that of the CP titanium castings.

Experimental Ti-Au alloys (5, 10, 20 and 40 mass% Au) were made. Mechanical properties and grindability of the castings of the Ti-Au alloys were examined. As the concentration of gold increased to 20%, the yield strength and the tensile strength of the Ti-Au alloys became higher without markedly deteriorating their ductility. This higher strength can be explained by the solid-solution strengthening of the a titanium. The Ti-40%Au alloy became brittle because the intermetallic compound Ti3Au precipitated intensively near the grain boundaries. There was no significant difference in the grinding rate and grinding ratio among all the Ti-Au alloys and the pure titanium at any speed.

To establish a method of determining the machinability of dental materials for CAD/CAM systems, the machinability of titanium, two titanium alloys (Ti-6Al-4V and Ti-6Al-7Nb), and free-cutting brass was evaluated through cutting force and spindle motor current. The metals were slotted using a milling machine and square end mills at four cutting conditions. Both the static and dynamic components of the cutting force represented well the machinability of the metals tested: the machinability of Ti-6Al-4V and Ti-6Al-7Nb was worse than that of titanium, while that of free-cutting brass was better. On the other hand, the results indicated that the spindle motor current was not sensitive enough to detect the material difference among the titanium and its alloys.

Objectives. The purpose of the present study was to evaluate the grindability of a series of cast Ti–Cu alloys in order to develop a titanium alloy with better grindability than commercially pure titanium (CP Ti), which is considered to be one of the most difficult metals to machine. Methods. Experimental Ti–Cu alloys (0.5, 1.0, 2.0, 5.0, and 10.0 mass% Cu) were made in an argon-arc melting furnace. Each alloy was cast into a magnesia mold using a centrifugal casting machine. Cast alloy slabs (3.5 mm×8.5 mm×30.5 mm), from which the hardened surface layer (250 μm) was removed, were ground using a SiC abrasive wheel on an electric handpiece at four circumferential speeds (500, 750, 1000, or 1250 m/min) at 0.98 N (100 gf). Grindability was evaluated by measuring the amount of metal volume removed after grinding for 1 min. Data were compared to those for CP Ti and Ti–6Al–4V. Results. For all speeds, Ti–10% Cu alloy exhibited the highest grindability. For the Ti–Cu alloys with a Cu content of 2% or less, the highest grindability corresponded to an intermediate speed. It was observed that the grindability increased with an increase in the Cu concentration compared to CP Ti, particularly for the 5 or 10% Cu alloys at a circumferential speed of 1000 m/min or above. Significance. By alloying with copper, the cast titanium exhibited better grindability at high speed. The continuous precipitation of Ti2Cu among the α-matrix grains made this material less ductile and facilitated more effective grinding because small broken segments more readily formed.

The ions released from conventional and high-copper amalgams in contact with titanium were quantitatively analyzed in a 0.9% NaCl solution at 37 degrees C when the surface area ratio of titanium/amalgam was set up as 1/10, 1/1, or 10/1. The corrosion potentials of the amalgams and titanium were measured under the same conditions. Surface analyses on the amalgams were also employed using SEM with WDS. Though the potential of the conventional amalgam was always lower than that of titanium, that of the high-copper amalgam was reversed during the early stage of immersion and remained lower. When the surface area ratio of titanium grew at 10/1, tin and copper ions released from the conventional and high-copper amalgam, respectively, increased significantly compared with those of each amalgam that was not in contact with titanium. The galvanic corrosion in such a large surface area of titanium possibly led to the heavy corrosion of the amalgams.

Experimental Ti-Ag alloys (5, 10, and 20 mass% Ag) and Ti-Cu alloys (2, 5, and 10 mass% Cu) were cast into magnesia molds using a dental casting machine, and their grindability was investigated. At the lowest grinding speed (500 m min(-1)), there were no statistical differences among the grindability values of the titanium and titanium alloys. The grindability of the alloys increased as the grinding speed increased. At the highest grinding speed (1500 m x min(-1)), the grindability of the 20% Ag, 5% Cu, and 10% Cu alloys was significantly higher than that of titanium. It was found that alloying with silver or copper improved the grindability of titanium, particularly at a high speed. It appeared that the decrease in elongation caused by the precipitation of small amounts of intermetallic compounds primarily contributed to the favorable grindability of the experimental alloys.

Pure titanium and titanium alloys are potential materials for the fabrication of cast dental appliances. One important factor in producing sound castings is the capacity of the metal to fill the mold. This study used a wedge-shaped mold to compare the mold filling of titanium with that of conventional dental casting alloys. The metals used were CP Ti, Ti-6Al-7Nb, Ti-6Al-4V, Ti with 1 and 4wt% Cu and ADA Type III gold alloy and an Ni-Cr alloy. The castings were cut into four pieces parallel to the triangular surface. Mold filling was evaluated as the distance between the tip of the cast wedge and theoretical tip of the triangle. The mold filling of the gold alloy was superior compared to all the metals tested, while the mold filling of the Ni-Cr alloy was the worst. There were no statistical differences at the 30 degrees marginal angle for all the cast titanium metals. At the sharper 15 degrees angle, CP Ti and Ti-6Al-7Nb was superior to both the Ti-Cu alloys. Although the mold filling of titanium was inferior compared to the gold alloy, the data justify the use of titanium for the production of dental appliances.

Effects of titanium plate in contact with amalgams of ‘Hi Atomic M’ (HA) and ‘Lumi Alloy’ (LM) on the release of metal ions from those amalgams into 0.9% NaCl solution were investigated using inductively coupled plasma atomic emission spectroscopy, electron probe microanalysis and XPS. Except for Hg, the release of ions increased about ten times on Ti contact, whereas that of Hg was diminished several-fold. No measurable amounts of Ti ions were found in solution. Where the Ti is in contact with the amalgam, every element was deposited almost proportionally to the solution composition. Tin oxide containing several percent of In2O3 covered the top surface of Ti connected to the conventional HA amalgam. However, the dominant species on Ti connected to the high-copper LM amalgam were Cu and Sn oxides. On the Ti connected to the amalgams, the concentrations of other elements were very low. Copyright © 2002 John Wiley & Sons, Ltd.

Titanium and some of its alloys are successfully used for biomaterials. The surface oxide films on these materials play important roles in maintaining corrosion resistance and biocompatibility. In this study, Ti‐6Al‐4V, Ti‐56Ni, and Ti‐ xZr (x = 0, 25, 50, 60, 75, 100) alloys in mass% were abraded and kept for 300 s in water and Hanks’ solution. The regenerated surface oxide film in Hanks’ solution was characterized using X-ray photoelectron spectroscopy. As a result, phosphate ions were preferentially taken up in the surface oxide film during regeneration. Ions constituting Hanks’ solution other than calcium and phosphate were absent from the surface oxide film. In the case of titanium and Ti‐ 6Al‐4V, calcium phosphate was formed on/in the surface oxide film regenerated in Hanks’ solution. However, Ti‐56Ni, Ti‐Zr, and zirconium did not form calcium phosphate on themselves but formed phosphate without calcium. These results are in good agreement with those for titanium alloys immersed in Hanks’ solution.

1Division of Dental Biomaterials, Department of Oral Rehabilitation and Materials Science, Tohoku University Graduate School of Dentistry, Sendai 980-8575, Japan 2Department of Dental Technology, Daegu Polytechnic College, Daegu 706-711, Korea 3Institute for Metals Research, Tohoku University, Sendai 980-557, Japan 4Department of Dental Materials, College of Dentistry, Kyungpook National University, Daegu 731-744, Korea

In this study, experimental Ti-Ag alloys (5, 10, and 20 mass% Ag) and Ti-Cu alloys (2, 5, and 10 mass% Cu) were made in an argon-arc melting furnace. The alloys were cast into magnesia molds using an argon gas-pressure dental casting machine, and the mechanical properties and microstructures of the castings were investigated. As the concentration of silver or copper in the alloys increased, the tensile strength, yield strength, and hardness of the alloys became higher than those of CP Ti, and the elongation of the alloys became lower than that of CP Ti. Changes in the mechanical properties by alloying were considered to be caused by solid-solution strengthening of the a-phases and by precipitation of intermetallic compounds.

The purpose of this study was to investigate flow characteristics of four commercial polyaddition-type silicone impression materials (Regular Type) before mixing.Base and catalyst pastes were filler and polymer separated by a centrifugal separator with benzene for component analysis. As a result, weight fraction of filler was 39-55% and the chief ingredient was silica. The main polymer of base and catalyst pastes was polydimethylsiloxane. Especially, base polymer included hydrogen polydimethylsiloxane which was a crosslinking agent. The molecular weight (Mw) of these polymer was mostly about 40, 000-70, 000.The viscosities of these pastes before mixing were measured by a cone-plate viscometer. Both base and catalyst pastes demonstrated pseudoplastic behavior which is the non-Newton flow. Particularly, base pastes showed thixotropic properties because of their clear hysteresis curves and time dependency on the viscosity. One of the base pastes had a yield value.The inorganic filler significantly affected on flow characteristics of impression materials. The results suggested a means to manufacture impression materials with superior characteristics for working.

In this study, the relationship between the composition and the flow properties of three commercial tissue conditioners was investigated. Analysis of the composition was chiefly done by infrared spectroscopy (IR). As for the liquid, plasticizer was qualitatively determined and the content of alcohol was measured by distillation. The characteristics of polymer powders were obtained by means of gel permeation chromatography (GPC), particle size analyzer and SEM. As for the flow property, the apparent viscosity of a mixture of liquid and powder was measured by a cone and plate rotational viscometer.As a result, the liquid was a mixture of a phthalic ester plasticizer (dibutyl phthalate) with up to 13% ethyl alcohol. The polymer powders generally consisted of polyethyl methacrylate (PEMA), but one was a blend of PEMA and polyisobutyl methacrylate (iso-PBMA).The viscosities of mixtures were found to increase rapidly with an increase in the ethyl alcohol content, and an increase in temperature. Further, the viscosity curve of the tissue conditioner, of which the powder was a blend of PEMA and iso-PBMA, showed characteristic behavior. Thus it was suggested that the flow property of the tissue conditioner was affected by the molecular structure of the polymer powder.

Experimentation in all aspects of titanium casting at universities and industries throughout the world for the last 20 years has made titanium and titanium-alloy casting nearly feasible for fabricating sound cast dental prostheses, including crowns, inlays, and partial and complete dentures. Titanium casting in dentistry has now almost reached the stage where it can seriously be considered as a new method to compete with dental casting using conventional noble and base-metal alloys. More than anything else, the strength of titanium’s appeal lies in its excellent biocompatibility, coupled with its comparatively low price and abundant supply. Research efforts to overcome some problems associated with this method, including studies on the development of new titanium alloys suitable for dental use, will continue at many research sites internationally.

The purpose of this study was to examine effects of magnetizing, methods on attractive forces in disk-type model and crown-type model which consisted of two kinds of Fe-Pt magnetic alloys (Fe-39.5Pt-0.75 Nb (mole%), Fe-39.5 Pt-0.65 Nb-0.1Si (mole%)). In addition the surface roughness and adaptability of the inner surfaces were examined in the crown-type model.The results were as follows:1. Surface roughness (crown-type samples)There was no significant difference between the alloys. As for the alloys, surface roughness was greater than that of the metal model.2. Adaptability (crown-type samples)The adaptability of the crown-type was loose. In order to keep the frictional forces as small as possible, the expansion of the investment was intentionally increased by the adjustment of the L/P ratio.3. Attractive forces1) Disk-type samplesThe attractive force of the disk-type was large when magnetized at four-poles on a plane and the attractive force of a sample was 734 gf on the average.2) Crown-type samplesThe attractive force observed with crown-type (magnetized along the crown axis, Fe-39.5 Pt-0.65 Nb-0.1 Si (mole%)) showed 536 gf on the average. This value was sufficient for retaining removable crowns and bridges.

The chemical structures and dynamic viscoelastic properties of the proprietary mouth-formed and custom-made mouthguards used in contact sports were investigated to evaluate shock absorption and moldability.The infrared spectra of the molecular structure of each material were identified as ethylene-vinyl acetate copolymer (EVA). The contents of vinyl acetate in EVA were 27-39 mass%. The weight average molecular weights measured by the gel permeation chromatography were 99, 000-150, 000.The master curves of storage modulus G′, dynamic viscosity η′ and loss tangent tanδat the reference temperature of 35°C were constructed from the data obtained at different temperatures, by the application of time-temperature superposition principle. By this method, it is possible to evaluate the viscoelastic properties expanded to both higher and lower frequencies than can be obtained experimentally.The difference of G′ and tanδfor each material was due to the vinyl acetate content and molecular weight in EVA. Marked effects of the molecular weight on the master curves of tanδwere observed in a lowfrequency range: the lower the molecular weight, the higher the tanδ.It was suggested that the shock absorption and moldability of mouthguards could be evaluated from the master curve of tanδ.

To optimize the properties of titanium for use in dentistry, alloying is necessary. This study reports on the characterization of some titanium alloys for grindability, wear, and corrosion resistance. Improvements in grindability and wear seemed to occur with the presence of the eutectoid in the alloy.

Titanium and titanium alloys are difficult to machine. This problem arises when milling, using dental CAD/CAM systems. In a previous study, an experimental binary titanium alloy with 20 mass% Ag showed good grindability. In this study, the fracture strength of porcelain fused to a Ti-20 mass% Ag alloy crown made using a CAD/CAM (GN-1, GC, Japan) system is investigated. As controls, similar pure titanium (JIS grade II) samples made using cast and using the CAD/CAM system were also examined. The crowns were made assuming a maxillary left central tooth. The fracture strengths were statistically analyzed using one-way ANOVA followed by Tukey pairwise tests. There was no significant difference in the fracture strength of porcelain fused to metal crowns between the Ti-20 mass% Ag alloy frame crowns and the pure titanium frame crowns.

We prepared experimental Ti–Ag alloys and investigated their properties. The strength and hardness of the Ti–Ag alloys increased with the concentration of Ag. Moreover, the alloys exhibited sufficient elongation, making them suitable for dental applications. The machinability of the Ti–Ag alloys was superior to that of pure titanium. By carrying out the anode polarization test and immersion test, we found that the corrosion resistance of the Ti–Ag alloys was comparable to that of pure titanium. Further, we performed a biofilm formation test and found that the amount of biofilm formed on the experimental Ti–Ag alloys was less than that on pure titanium, pure silver, and a dental alloy. It was concluded that the experimental Ti–Ag alloys are new types of biomaterials that have an inhibitory effect on biofilm formation as well as excellent mechanical properties and outstanding machinability.

This study electrochemically evaluated corrosion resistance of commercially available cup yoke type magnetic assemblies. Anodic polarization curves in 0.9% NaCl solution at 37°C showed that the magnetic assemblies tested in this study broke down at the range of 0.75–1.3 V because of pitting corrosion in the vicinity of the shield ring of 316L. However, the pitting potentials were significantly higher than that of 316L (P < 0.05). EPMA showed increase in Cr content on the surface of shield ring compared to its inside (P < 0.05) because the welding bead deeply covered the surface of shield ring. The laser welding resulted in increasing the pitting potentials of magnetic assemblies.

A dental magnetic attachment is used for over-dentures, removable partial dentures, and orthodontic and maxillofacial prostheses. The dental magnetic attachment is composed of a magnetic assembly and a keeper. The magnetic attractive force between the magnetic assembly and the keeper is used as the retention. The magnetic assembly is composed of a small Nd—Fe—B magnet that is covered within a magnetic stainless steel yoke and a non-magnetic stainless steel spacer. The keeper is also made of magnetic stainless steel. The yoke of the magnet assembly and the keeper form a closed magnetic circuit, which is necessary to concentrate on the magnetic flux and make efficient use of it. The covering nonmagnetic stainless steel and magnetic stainless steel yoke are welded seamlessly using micro-laser to protect the magnet from corrosion. In an oral cavity, the keepers and the magnetic assemblies are contacted with root caps made of dental precious alloys. It is important to examine the galvanic corrosion behavior of those stainless steels with dental precious alloys from the electrochemical properties and released ions. The dental magnetic attachment was implanted in rabbit tibia to investigate the influence of the static magnetic flux on hard tissue.

This study is an examination of the released ions from dental cast experimental Ti-Ag alloys by an immersion test. Ti-Ag alloys (5–25mass%Ag) and pure titanium (control) were cast into magnesia molds; the hardened surface layer was then removed. After each specimen was immersed in aerated 0.9% NaCl or 1% lactic acid solution at 37°C for 7 days, released ions were analyzed using inductively coupled plasma. Cast Ti-Ag alloys with Ag ≤ 20% formed a single α structure. Ti and Ag ions were not detected from the alloys and pure titanium in the NaCl solution. The microstructures of cast Ti-Ag alloys with 22.5% Ag and 25% Ag consisted of α + intermetallic compounds (Ti2Ag or Ti2Ag + TiAg). A small amount of Ti and Ag ions was detected from some of the 22.5% Ag and 25% Ag specimens in the NaCl solution. The preferential dissolution of parts of the intermetallic compounds was observed in the specimens after the test. In the lactic acid solution, a significantly smaller amount of Ti ions was released from all the Ti-Ag alloys than from pure titanium. Ag ions were not detected. The intermetallic compounds remained on the specimen surfaces after the test in the lactic acid solution.

An object of this study was to examine the mold filling capacity of some Ti-Hf alloys. Regardless of the edge angle, the Ti-Hf alloys behaved similar to commercially pure (CP) Ti due to their isomorphous nature of solidifying congruently over the ranges of the alloys examined.

The Young’s moduli of experimental binary titanium alloys with Cu, Ag, Au, Zr, Nb, or Hf (up to 30 mass%) were determined. As the concentration of Cu increased, the Young’s modulus monotonically increased. As the concentration of Ag, Au, or Nb increased to 20%, the Young’s modulus decreased, followed by a subsequent increase in value. The Young’s modulus monotonically decreased with the increase in the Zr concentration. A slight increase in the Young’s modulus was present when titanium was alloyed with Hf.

This study is an investigation of the bond strength of porcelain to pure titanium, cast and machined by CAD/CAM processes, and a determination of the fracture strength of porcelain fused to pure titanium crown by both methods. The bond strength was evaluated according to the surface treatment conditions. The mean bond strengths were ranged from 36.1 to 49.4 MPa. The surface treatment conditions had a significant effect on the bond strength. The mean fracture strength for the cast frame crowns was 1667 N, and that for the machined frame crowns was 1554 N. There was no significant difference between the two methods. Acceptable bond strength and fracture strength were achieved by both methods.

In this study, we examined the corrosion behavior of dental precious alloys and magnetic stainless steels, namely SUS 444, SUS XM27, and SUS 447J1, used for dental magnetic attachments. Their galvanic corrosion behavior was evaluated from the viewpoint of corrosion potentials when they were in contact with each other. Rest potentials of the precious alloys were constantly higher than those of magnetic stainless steels. Since most gold alloys raised the corrosion potential more significantly than silver alloys did, silver alloys seemed to be better suited than gold alloys for combination with magnetic stainless steels. However, all corrosion potential values were sufficiently lower than the breakdown potentials of the stainless steels and existed within their passive regions. Based on the findings of this study, SUS XM27 and SUS 447J1 — which exhibited higher breakdown potentials than SUS 444 — emerged as the preferred choices for combination with gold alloys.

PURPOSE For the purpose of evaluating the flow properties influencing the formativeness of commercial hard resin pastes used in the construction of crowns and bridges, we examined the behaviors of various resin pastes and their temperature dependence during manipulation. METHODS Five types of hard resins currently in use for the construction of crowns and bridges in the clinical setting, namely, New Meta Color INFIS, Solidex, Ceramage, Gradia, and Estenia C&B, were examined. The components and flow properties of each resin paste were investigated in relation to the dentine and enamel colors. The viscosities of the resin pastes before curing were measured by a cone-plate viscometer. RESULTS Each resin paste demonstrated a non-Newtonian flow, and the flow curve showed a hysteresis loop, in which the upward and downward curves were different. When the shear stress at the beginning of the holding time of the flow curve (20 degrees C, 25 degrees C, 30 degrees C) of each resin paste was measured, the shear stress at 20 degrees C was found to be significantly higher than that at 25 degrees C and 30 degrees C, and the shear stress at 25 degrees C was found to be significantly higher than that at 30 degrees C. The viscosity was found to be higher at lower temperatures than at higher temperatures. Comparison of the shear stresses at the beginning and at the end of the holding time revealed that the stress at the beginning of the holding time was significantly higher than that at the end of the holding time for all except the Estenia C&B resin paste. CONCLUSIONS Each of the resin pastes used in the present study showed temperature dependence of its characteristics in the temperature range examined (20-30 degrees C) and thixotropic fluidity. However, the flow characteristics of these resin pastes differed significantly, suggesting that the flow characteristics may affect the manipulation of resin formativeness.

Objective: To examine the mechanical properties and the usefulness of titanium-niobium-aluminum (Ti-Nb-Al) wire in orthodontic tooth movement as compared with nickel-titanium (Ni-Ti) wire. Materials and Methods: The load deflection of expansion springs was gauged with an original jig. The gradient of the superelastic region was measured during the unloading process. Expansion springs comprising the two types of alloy wires were applied to upper first molars of rats. The distance between the first molars was measured with micrometer calipers. Results: The force magnitude of the Ti-Nb-Al expansion spring was lower than that of the Ni-Ti expansion spring over the entire deflection range. The initial force magnitude and the gradient in the superelastic region of the Ti-Nb-Al expansion springs were half those of the Ni-Ti expansion springs. Thus, Ti-Nb-Al expansion springs generated lighter and more continuous force. Tooth movement in the Ni-Ti group proceeded in a stepwise fashion. On the other hand, tooth movement in the Ti-Nb-Al group showed relatively smooth and continuous progression. At 17 days after insertion of expansion springs, there were no significant differences between the Ti-Nb-Al and Ni-Ti groups in the amount of tooth movement. Conclusions: These results indicate that Ti-Nb-Al wire has excellent mechanical properties for smooth, continuous tooth movement and suggest that Ti-Nb-Al wire may be used as a practical nickel-free shape memory and superelastic alloy wire for orthodontic treatment as a substitute for Ni-Ti wire.

The electrochemical properties and released ions of binary Au-1.6mass%Ti alloy were evaluated in 0.9% NaCl and 1% lactic acid solutions and compared with those of Au-Ag-Pd alloy and Type 4 gold alloy. Rest potential and anodic polarization curve of Au-1.6mass%Ti alloy were almost the same as those of pure gold regardless of thermal condition (softening, hardening, or as cast). Among the alloys in comparison, the anodic polarization curve of Au-1.6mass%Ti alloy showed that it had the least current density and best stability when subject to electrochemical oxidation. Though Au-1.6mass%Ti alloy did release a small amount of Ti ions in 1% lactic acid solution, the amount of released Ti ions was not more than 1/5 of the amount released by pure titanium under the same condition. In the same vein, the total amount of ions released from Au-1.6mass%Ti alloy was much lower than that of the precious alloys in both solutions.