Inhibitory effect of Ti-Ag alloy on artificial biofilm formation.

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<0.05). In addition, Ti-Ag alloys and pure Ti were not bactericidal, although pure Ag and Ag-Pd alloy killed bacteria. These results suggest that Ti-20% Ag and Ti-25% Ag alloys are suitable for dental material that suppresses biofilm formation without disturbing healthy oral microflora.

Galvanic corrosion of ferritic stainless steels used for dental magnetic attachments in contact with an iron-platinum magnet.

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.

Machinability of experimental Ti-Ag alloys.

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.

Galvanic corrosion between dental precious alloys and magnetic stainless steels used for dental magnetic attachments.

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.

[Rheological study of hard resin for crown and bridge].

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.

Electrochemical behavior of cast Ti-Ag alloys.

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.

Orthodontic buccal tooth movement by nickel-free titanium-based shape memory and superelastic alloy wire.

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.

Fit of metal ceramic crowns cast in Au-1.6 wt% Ti alloy for different abutment finish line curvature.

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.

Elastic moduli of cast Ti-Au, Ti-Ag, and Ti-Cu alloys.

OBJECTIVES: This study investigated the effect of alloying titanium with gold, silver, or copper on the elastic properties of the alloys. METHODS: A series of binary titanium alloys was made with four concentrations of gold, silver, or copper (5, 10, 20, and 30 mass%) in an argon-arc melting furnace. The Young's moduli and Poisson's ratios of the alloy castings were determined with an ultrasonic-pulse method. The density of each alloy was previously measured by the Archimedes' principle. Results were analyzed using one-way ANOVA and the Scheffé's test. RESULTS: The densities of Ti-Au, Ti-Ag, and Ti-Cu alloys monotonically increased as the concentration of alloying elements increased. As the concentration of gold or silver increased to 20%, the Young's modulus significantly decreased, followed by a subsequent increase in value. As the concentration of copper increased, the Young's modulus monotonically increased. The Young's moduli of all the Ti-Cu alloys were significantly higher than that of the titanium. SIGNIFICANCE: The density of all the experimental alloys was virtually independent of the alloy phases, while the Young's moduli and Poisson's ratios of the alloys were dependent. The addition of gold or silver slightly reduced the Young's modulus of the titanium when the alloy phase was single alpha. The increase in the Young's modulus of the Ti-Cu alloys is probably due to the precipitation of intermetallic compound Ti2Cu. Copper turned out to be a moderate stiffener that gains a Young's modulus of titanium up to 20% at the copper concentration of 30 mass%.

Grindability of cast Ti-Hf alloys.

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.

Effect of heat history on the corrosion of ferritic stainless steels used for dental magnetic attachments.

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.

Electrochemical properties and released ions of Au-1.6mass%Ti alloy.

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.

Grindability of dental magnetic alloys.

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.

Ceramic bonding strength of Au-1.6 wt% Ti alloy.

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.

Corrosion characteristics of alpha-Ti and Ti2Cu composing Ti-Cu alloys.

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.

Mechanical properties of cast Ti-Hf alloys.

This study examined the mechanical properties of a series of Ti-Hf alloys. Titanium alloys with 10 to 40 mass % Hf were made with titanium and hafnium sponge in an argon-arc melting furnace. Specimens cast into magnesia-based investment molds were tested for yield strength, tensile strength, percentage elongation, and modulus of elasticity. Vickers microhardness was determined at 25 to 600 microm from the cast surface. X-ray diffractometry was also performed. Commercially pure Ti (CP Ti) and pure Ti prepared from titanium sponge were used as controls. The data (n = 5) were analyzed with a one-way ANOVA and the Student-Newman-Keuls test (alpha = 0.05). The diffraction peaks of all the metals matched those for alpha Ti; no beta phase peaks were found. Alloys with Hf > or = 25% had significantly (p < 0.05) higher yield and tensile strength compared to the CP Ti and pure Ti. There were no significant differences (p > 0.05) in elongation among all the Ti-Hf alloys and CP Ti, whereas the elongation of alloys with Hf > or = 30% was significantly (p < 0.05) lower than that of the pure Ti. The cast Ti-Hf alloys tested can be considered viable alternatives to CP Ti because they were stronger than CP Ti and had similar elongation.

The thickness effects of titanium castings on the surface reaction layer.

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.

Corrosion behavior and microstructures of experimental Ti-Au alloys.

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.

Mechanical properties and grindability of experimental Ti-Au alloys.

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.

Machinability evaluation of titanium alloys.

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.