Photocatalytic antibacterial effect of TiO(2) film of TiAg on Streptococcus mutans.

OBJECTIVE: To test through various oxidation procedures the differences in antibacterial activities against Streptococcus mutans (S mutans) of Titanium (Ti) and Titanium silver (TiAg) metals coated with TiO(2). MATERIALS AND METHODS: This study examined the photocatalytic antibacterial effects on S mutans of Ti and TiAg ubstrates coated with two crystalline forms of TiO(2) by thermal and anodic oxidation. A bacterial suspension of S mutans was pipetted onto TiO(2)-coated metal specimens and uncoated specimens with ultraviolet A (UVA) illumination for 20 to 100 minutes. The same specimen without UVA was used as the control. The level of colony-forming units of S mutans after UVA illumination was compared with that of the control. RESULTS: The level of colony-forming units of S mutans was significantly lower on TiO(2)-coated Ti and TiAg metal specimens after UVA illumination than on uncoated Ti and TiAg specimens. The level of colony-forming units of S mutans was significantly lower on the metals coated by anodic oxidation than on those coated by thermal oxidation. The TiO(2) coating on TiAg had a significantly higher and more rapid antibacterial effect than did the TiO(2) coating on Ti. CONCLUSIONS: The antibacterial effect of a TiO(2) film formed by anodic oxidation was superior to that formed by thermal oxidation. The addition of Ag to the Ti specimen indicated a synergistic effect on the photocatalytic antibacterial property against S mutans.

Properties of experimental titanium-silver-copper alloys for dental applications.

The aim of this study was to develop Ti-Ag-Cu alloys with a higher corrosion resistance, better biocompatibility, and better mechanical properties than commercially pure titanium and its alloys. The microstructure, corrosion resistance, mechanical property and cytotoxicity of the Ti-Ag-Cu alloys were investigated. The corrosion resistance was evaluated by open circuit potential measurements and potentiodynamic polarization tests in artificial saliva at 37 degrees C. The mechanical properties were evaluated using tensile and microhardness tests. The biocompatibility was tested by evaluating the cytotoxicity of the alloys using an agar-overlay test and MTT assay. It was found that the open circuit potentials of the Ti-Ag-Cu alloys were higher than that of pure Ti. However, the passive current densities of the Ti-Ag-Cu alloys were similar to that of pure titanium. The mechanical properties improved with increasing Ag and Cu content. All the Ti-Ag-Cu alloys examined were found to be noncytotoxic similar to pure Ti. Therefore, Ti-Ag-Cu alloys can be used as biomaterials in the dental field.

Influences of passivating elements on the corrosion and biocompatibility of super stainless steels.

Biometals need high corrosion resistance since metallic implants in the body should be biocompatible and metal ion release should be minimized. In this work, we designed three kinds of super stainless steel and adjusted the alloying elements to obtain different microstructures. Super stainless steels contain larger amounts of Cr, Mo, W, and N than commercial alloys. These elements play a very important role in localized corrosion and, thus, their effects can be represented by the "pitting resistance equivalent number (PREN)." This work focused on the behavior which can arise when the bare surface of an implant in the body is exposed during walking, heavy exercise, and so on. Among the experimental alloys examined herein, Alloy Al and 316L stainless steels were mildly cytotoxic, whereas the other super austenitic, duplex, and ferritic stainless steels were noncytotoxic. This behavior is primarily related to the passive current and pitting resistance of the alloys. When the PREN value was increased, the passivation behavior in simulated body solution was totally different from that in acidic chloride solution and, thus, the Cr(2)O(3)/Cr(OH)(3) and [Metal oxide]/[Metal + Metal oxide] ratios of the passive film in the simulated body solution were larger than those in acidic chloride solution. Also, the critical current density in simulated body solution increased and, thus, active dissolution may induce metal ion release into the body when the PREN value and Ni content are increased. This behavior was closely related to the presence of EDTA in the simulated body solution.

Cytocompatibility and electrochemical properties of Ti-Au alloys for biomedical applications.

The purpose of this study was to develop Ti-Au alloys with a higher resistant to corrosion, better biocompatibility, and better mechanical properties than the commercially pure titanium and its alloys. Ti-Au alloys were designed with a gold content that ranged from 0 to 5.0 at % in steps of 1.0 at %. Properties of the alloys including chemical composition, microstructure, phase, hardness, electrochemical properties, and the cytotoxicity were investigated. Only the alpha phase existed in the Ti-Au alloys. The addition of gold to the titanium decreased the alpha to beta transformation temperature. The acicular alpha phase became thinner and the hardness value increased with increasing gold content. In the electrochemical tests, Ti-Au alloys had a higher resistant to corrosion than had pure titanium and did not exhibit pitting corrosion in artificial saliva. The cytotoxicities of the Ti-Au alloys were similar to that of pure titanium. Therefore, Ti-Au alloys could be used as biomaterials in the medical and dental fields.

Photocatalytic antibacterial effect of TiO(2) film formed on Ti and TiAg exposed to Lactobacillus acidophilus.

When irradiated under near-ultraviolet (UV) light, TiO(2) exhibits strong bactericidal activity. The TiO(2) photocatalyst would be effective on orthodontic appliances after its antibacterial effect on the carcinogenic microorganism Lactobacillus acidophilus is evaluated. To compare the antibacterial effect of two crystalline forms of TiO(2), rutile and anatase, thermal oxidation and anodic oxidation were employed to form each structure, respectively. The antibacterial effect of TiO(2) film on TiAg was also compared with that on Ti. Bacterial solutions were pipetted onto the TiO(2)-coated specimen and illuminated with UVA (2 x 15 W, black light, 356 nm) up to 100 min and the reaction solutions were incubated to count the colony-forming units. The antibacterial activity of the coated specimens was similar to that of the uncoated group. The antibacterial activity of the coated specimens of TiAg was not different from that of Ti. TiO(2) coatings formed on both Ti and TiAg specimens did not exhibit cytotoxicity on the L-929 cells of mice.

Effect of silver addition on the properties of nickel-titanium alloys for dental application.

Equiatomic and near-equiatomic nickel-titanium alloys exhibit a shape-memory effect and superelasticity. However, the properties of such alloys are extremely sensitive to the precise nickel-titanium ratio and the addition of alloying elements. High corrosion resistance is necessary for biomedical applications, especially orthodontic. The purpose of this study was to investigate the effect of silver addition to nickel-titanium alloys for dental and medical application. Arc melting, homogenization, hot rolling, and solution heat treatment were performed to prepare the nickel-titanium-silver (NiTi-Ag) specimens. The properties of the ternary NiTi-Ag alloys such as phase-transformation temperature, microstructure, microhardness, corrosion resistance, and cytotoxicity were investigated. The NiTi-Ag alloys showed low silver recovery rate for the cast alloy, due to silver's low evaporation temperature, and low silver solubility in nickel-titanium. Silver addition to nickel-titanium increased the transition temperature range to 100 degrees C and stabilized the martensitic phase (monoclinic structure) at room temperature, because the martensitic transformation starting temperature (Ms) was above room temperature. Martensitic and austenitic phases existed in X-ray diffraction patterns of solution-annealed NiTi-Ag alloys. The silver addition was considered to improve the corrosion resistance and form a stable passive film. Significantly, the mechanical properties of the silver-added alloys were dependent upon the amount of alloying addition. There was no toxicity in the NiTi-Ag alloys, as the response index showed none or mild levels.

Ion release and cytotoxicity of stainless steel wires.

Heat treatment is generally applied to orthodontic stainless steel (SS) wires to relieve the stresses that result from their manipulation by orthodontists. The quality and thickness of the oxide films formed on the surface of heat-treated wires can vary, and it is believed that these oxide films can influence the properties of heat-treated wires. The aim of this study was to investigate the influence of heat treatment and cooling methods on the amount of metal ions released and to examine the cytotoxicity of heat-treated wires. In this study, four types of SS wires (Remanium, Permachrome, Colboloy and Orthos) with a cross-sectional area of 0.41 x 0.56 mm were investigated. These wires were heat-treated in a vacuum, air, or argon environment, and were cooled in either a furnace or a water bath. Four control groups and 24 experimental groups were classified according to the type of wires, heat treatment conditions and cooling methods. In each group, the amount of nickel released as well as its cytotoxicity was investigated. The concentration of dissolved nickel ions in artificial saliva was measured for a period of up to 12 weeks. In all groups, the concentration of dissolved nickel ions in artificial saliva was lowest for the vacuum heat treatment-furnace cooling group and a significant difference was shown compared with the other experimental groups. The concentration of dissolved nickel ions in artificial saliva was highest in the groups heat-treated in air (P < 0.05), while the amount of nickel released was highest in the Remanium and Colboloy (P < 0.05). The cytotoxicity was mild in all the experimental groups but the response index of the air groups was slightly higher than in the other groups. According to these results, SS wires retain their high corrosion resistance and low ion release rate when heat-treated in a vacuum and cooled in a furnace.

A stainless steel bracket for orthodontic application.

Aesthetics has become an essential element when choosing orthodontic fixed appliances. Most metallic brackets used in orthodontic therapy are made from stainless steel (SS) with the appropriate physical properties and good corrosion resistance, and are available as types 304, 316 and 17-4 PH SS. However, localized corrosion of these materials can frequently occur in the oral environment. This study was undertaken to evaluate the accuracy of sizing, microstructure, hardness, corrosion resistance, frictional resistance and cytotoxicity of commercially available Mini-diamond (S17400), Archist (S30403) and experimentally manufactured SR-50A (S32050) brackets. The size accuracy of Mini-diamond was the highest at all locations except for the external horizontal width of the tie wing (P < 0.05). Micrographs of the Mini-diamond and Archist showed precipitates in the grains and around their boundaries. SR-50A showed the only austenitic phase and the highest polarization resistance of the tested samples. SR-50A also had the highest corrosion resistance [SR-50A, Mini-diamond and Archist were 0.9 x 10(-3), 3.7 x 10(-3), and 7.4 x 10(-3) mm per year (mpy), respectively], in the artificial saliva. The frictional force of SR-50A decreased over time, but that of Mini-diamond and Archist increased. Therefore, SR-50A is believed to have better frictional properties to orthodontic wire than Mini-diamond and Archist. Cytotoxic results showed that the response index of SR-50A was 0/1 (mild), Mini-diamond 1/1 (mild+), and Archist 1/2 (mild+). SR-50A showed greater biocompatibility than either Mini-diamond or Archist. It is concluded that the SR-50A bracket has good frictional property, corrosion resistance and biocompatibility with a lower probability of allergic reaction, compared with conventionally used SS brackets.

Properties of titanium-silver alloys for dental application.

The purpose of this study was to develop titanium-silver alloys with biocompatibility, high corrosion resistance, and low ion-release rate, and to evaluate the electrochemical properties of titanium-silver alloys in artificial saliva. Titanium-silver alloys with silver contents ranging from 0 to 4.5 at % in steps of 0.5 at % were designed. The alloys were arc melted, homogenized at 950 degrees C for 72 h, hot rolled to 2 mm in thickness, and finally solution heat treated at 950 degrees C for 1 h and quenched in water. Chemical compositions, phases, hardnesses, electrochemical properties, and the cytotoxicity of the alloys were investigated. The purity of titanium-silver alloys was maintained above 99.9%, because few impurities were introduced through their manufacture. In the case of alloys containing silver in the range 2.0-4.0 at %, the formation of an acicular alpha phase was observed inside the beta phase. The acicular phase got thinner with increasing amounts of silver. This means that silver is a beta-phase stabilizing element in titanium-silver alloys. The hardness value tended to rise with increasing silver content and increased largely over 3.5 at %, and the increase of the hardness value versus pure titanium was about 33%. It is believed that the substantial increases in hardness was due to the effects of solid solution strengthening and of alpha-beta phase transition. Moreover, titanium-silver alloys had higher corrosion resistances than pure titanium. These results mean that silver additions to titanium can improve alloy corrosion resistance. Passive current densities in the potentiodynamic polarization curves were dependent on the chemical compositions of the titanium-silver alloys. However, they did not show a linear relationship with respect to silver contents. Titanium-silver alloys did not show pitting corrosion in artificial saliva. It is believed that silver addition to titanium strengthened the passive film due to titanium dissolution induced by the different electromotive forces of titanium and silver. In the agar overlay test, the cytotoxicity of the titanium-silver alloys and of titanium were none or mild. In summary, titanium-silver alloys had higher mechanical properties and corrosion resistance than titanium, and toxicities that were similar to titanium. Therefore, it is recommended that titanium-silver alloys be adopted cautiously by the biomedical and dental fields.

Corrosion resistance of titanium-silver alloys in an artificial saliva containing fluoride ions.

Dental gels and rinses for caries prophylactic contain fluoride at concentrations ranging from 0.1 to 1%. In addition, many types of fluoride-releasing materials have been used in dental applications. The purpose of the study was to investigate the addition effect of fluoride into artificial saliva on the corrosion resistance of pure titanium and titanium-silver alloys. Titanium and titanium-silver alloys were arc melted, homogenized at 950 degrees C for 72 h, hot rolled, and solution heat treated and quenched. In order to investigate the effect of the fluoride ions on the corrosion resistance, potentiodynamic polarization testing, potentiostatic testing, and open-circuit potential measurements were performed in plain artificial saliva and 0.1 and 1% NaF-added artificial saliva. The passive current densities of titanium and titanium-silver alloys increased with increasing fluoride-ion concentration. Ti2.0Ag and Ti3.0Ag exhibited a low current density relatively and showed a stable behavior compared to titanium. The open-circuit potential of titanium decreased and current density at 250 mV (SCE) potentiostatic testing reacted sensitively with increasing fluoride concentration. On the other hand, the open-circuit potential of titanium-silver alloys with a high silver content (3.0-4.0 at %) reacted less sensitively to the fluoride-ion concentration. Among titanium-silver alloys, Ti3.0Ag alloy had a higher resistance against the attack of fluoride ions and showed a more stable open-circuit potential and current density than titanium in the fluoride-containing solution. It is concluded that they are electrochemically stable and maintained good corrosion resistance in fluoride-containing artificial saliva.

Electrochemical properties of suprastructures galvanically coupled to a titanium implant.

In recent years, dental implants have been widely used for the aesthetic and functional restoration of edentulous patients. Dental implants and restorative alloys are required with high corrosion resistance. Suprastructures and implants of different compositions in electrical contact may develop galvanic or coupled corrosion problems. In addition to galvanic corrosion, crevice and pitting corrosion may occur in the marginal gap between dental implant assemblies. In this study, gold, silver-palladium, cobalt-chromium, and nickel-chromium suprastructures were used to investigate their galvanic and crevice corrosion characteristics in combination with titanium (Ti) implants. Potentiodynamic and potentiostatic testing were performed in artificial saliva at 37 degrees C. Potentiodynamic testing was carried out at the potential scan rate of 1 mV/s in the range of -600-1600 mV (SCE). Potentiostatic testing was performed with an open-circuit potential and current densities at -250, 0, and 250 mV (SCE) in artificial saliva. After electrochemical testing, surface morphologies and cross-sections were examined using micrographs of the samples. Potentiodynamic test results indicated that suprastructure/Ti implant couples produced passive current densities in the range of 0.5-12 microA/cm(2); Ti abutment/Ti implant and gold/Ti implant couples exhibited relatively low passive current densities; Co-Cr/Ti implant couples the highest. Co-Cr and Ni-Cr/Ti implant couples showed breakdown potentials of 700 and 570 mV (SCE), respectively. The open-circuit potentials of silver, Ti abutment, gold, Ni-Cr, and Co-Cr/Ti implant couples were -93.2 +/- 93.9, -123.7 +/- 58.8, -140.0 +/- 80.6, -223.5 +/- 35.1, and -312.7 +/- 29.8 mV (SCE), respectively, and did not change with immersion time. The couples exhibited cathodic current densities at -250 mV (SCE); in particular, gold and silver alloys showed high cathodic current densities of -3.18 and -6.63 microA/cm(2), respectively. At 250 mV (SCE), Ti abutment/Ti implant couples exhibited a minimum current density of 9.48 x 10(-2) microA/cm(2), but gold, Ni-Cr, Co-Cr, and silver/Ti implant couples exhibited 0.313, 1.27, 5.60, and 8.06 microA/cm(2), respectively. All couples exhibited relatively low current densities at 0 mV (SCE). Photomicrographs after electrochemical testing showed crevice or pitting corrosion in the marginal gap and at the suprastructure surface. Although of the tested samples Co-Cr/Ti implant couples showed the possibility of galvanic corrosion, its degree was not significant. However, it should be borne in mind that galvanic corrosion can accelerate localized corrosion, such as crevice or pitting corrosion.

Properties of super stainless steels for orthodontic applications.

Orthodontic stainless-steel appliances are considered to be corrosion resistant, but localized corrosion can occur in the oral cavity. This study was undertaken to evaluate the properties of super stainless steels in orthodontic applications. Accordingly, the metallurgical properties, mechanical properties, corrosion resistance, amount of the released nickel, cytotoxicity, and characteristics of the passive film were investigated. Corrosion resistances of the specimens were high and in the following order: super austenitic stainless steel (SR-50A) > super ferritic stainless steel (SFSS) = super duplex stainless steel (SR-6DX) > 316L SS > super martensitic stainless steel (SR-3Mo) in artificial saliva, 37 degrees C. At 500 mV (SCE), current densities of SR-50A, SFSS, SR-6DX, 316L SS, and SR-3Mo were 5.96 microA/cm(2), 20.3 microA/cm(2), 31.9 microA/cm(2), 805 microA/cm(2), and 5.36 mA/cm(2), respectively. Open circuit potentials of SR-50A, 316L SS, SR-6DX, SR-3Mo, and SFSS were - 0.2, - 0.22, - 0.24, - 0.43, and - 0.46 V (SCE), respectively. SR-50A, SFSS, and SR-6DX released below 3 ng/ml nickel for 8 weeks, and increased a little with immersion time, and 316L SS released about 3.5 ng/ml nickel, but SR-3Mo released a large amount of nickel, which increased with immersion time. The study demonstrated that SR-50A, SR-6DX, and SFSS have high corrosion resistance and mild or no cytotoxicity, due to the passive film enhanced by synergistic effect of Mo + N or by high addition effect of Cr + W. All super stainless steels showed very low cytotoxicity regardless of their nickel contents, although SR-3Mo was found to be relatively cytotoxic. From these studies, these steels are considered suitable for orthodontic applications.

In vitro surface corrosion of stainless steel and NiTi orthodontic appliances.

Simulated fixed orthodontic appliances were constructed, immersed and incubated in artificial saliva for periods up to three months. Two types of stainless steel archwires and two types of NiTi wires were used. The surface corrosion of the archwires was determined macroscopically, with scanning electron microscopy, and with spectrophotometry. The deposits on the wires were identified with X-ray diffraction. Uniform corrosion was observed on stainless steel wires, and a slight colour change was detected on the NiTi wires beneath stainless steel ligatures. The corrosion product on the stainless steel wires increased with immersion time, and the surface oxide films were easily detached from the underlying matrix. Crevice corrosion was observed under deposits of oxide, and at the interface between bracket and band. Such corrosion may weaken a wire or weld leading to fracture. In contrast, the NiTi archwires did not corrode, and there was no significant difference in surface morphology. The stainless steel archwires showed a significant loss of reflectance after heat treatment and immersion in artificial saliva. The NiTi archwires had the same reflectance before and after the immersion test. NiTi archwires are significantly more stable and resistant to corrosion than stainless steel archwires.