Keun-Taek Oh

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.

Corrosion Wear of High Molybdenum and Nitrogen Stainless Steel for Biomedical Applications

The corrosion-wear property of high molybdenum and nitrogen stainless steel (UNS no. S32050) was investigated and compared with that of Ti, Ti6Al4V, CoCrMo, and 316L stainless steel used conventionally for biomedical applications. The corrosion resistance and corrosion-wear resistance of S32050 were examined using electrochemical methods. The stability of the passive film in a corrosion-wear system was evaluated. The corrosion-resistance of S32050 is as good as Ti alloys, because its passive film was enhanced due to the synergistic effect of the large amount of Mo and N addition. Therefore, it is predicted that S32050 can minimize the toxic effects by the released ions. The wear loss of UHMWPE (ultrahigh molecular weight polyethylene) to S32050 was less than that to Ti6A14V and 316L stainless steel, and similar to the CoCrMo. There were no scratches on the S32050 surface after the corrosion-wear test. S32050 had a low current density and high pitting potential under wear and had corrosion-wear properties superior to Ti6Al4V and similar to the CoCrMo in Hanks solution. S32050 with good corrosion-wear resistance could supplement the deficiencies of Ti alloys and CoCrMo. Thus, S32050 is considered to have the probability to be good metallic material for biomedical applications.

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.

In vitro corrosion resistance of orthodontic super stainless steel wire

Generally, orthodontic stainless steel wires are made with 18-8 stainless steel, but because of the low localized corrosion resistance of this steel, the probability of corrosion is high. The desired properties for wires to be used in the oral cavity include high corrosion resistance and optimal mechanical properties. The metallurgical properties, corrosion resistance, and ion release properties of rectangular wire produced experimentally with super stainless steel (S32050) by a drawing process were evaluated, these properties compared with Remanium, Permachrome, G&Hwire, and Orthos, and the consequent capability of this steel to satisfy the optimal property levels required for orthodontic wire are discussed. Except for S32050, the wires formed twinned martensite in severely deformed grains. S32050 exhibited a low current density of about 1.6 μA/cm 2 and a stable passive region in artificial saliva, but the comparative wires displayed high current density because of pitting that occurred above the breakdown potential. S32050 released only a small amount of nickel into the solution in spite of its high nickel content. The high corrosion resistance of S32050 wire inhibits the release of metallic ions in the oral cavity and therefore satisfies the requirements of orthodontic wire.

In Vitro Corrosion Resistance of Orthodontic Super Stainless Steel Wire The Effects of Stress Relieving Heat-Treatment

Generally, orthodontic stainless steel wires are made from 18-8 stainless steels hut because of their low resistance to localized corrosion, corrosion can still occur easily in the oral cavity. Therefore for the present study, rectangular wire was produced experimentally with super stainless steel (SR-50A), which then underwent stress relieving heat-treatment in air. argon, or vacuum, at 500°C, for 6 min, followed finally by either quenching or furnace cooling. The corrosion resistance and ion release properties of the wires were investigated. SR-50A exhibited a low current density of about I μA/cm 2 and a stable passive region in artificial saliva. Meanwhile, the comparative wires displayed a high current density because of the pitting that occurred above the breakdown potential. SR-50A heat-treated in either vacuum or argon demonstrated high corrosion resistance and a low ion release rate irrespective of the cooling method, but the SR-50A heat-treated in air exhibited low corrosion resistance. The comparative wires, heat-treated in air or quenched, showed very low corrosion resistance and a high ion release rate due to their porous and nonprtitective film. SR-50A was less sensitive to the heat-treatment conditions than the comparative wires, and further was able to inhibit the release of metallic ions in the oral cavity. Therefore, these properties of SR-50A are considered to satisfy all the requirements for the safe application of orthodontic wire.

Biological evaluation of micro-nanoporous layer on Ti–Ag alloy for dental implant

Abstract This study examined the biocompatibility of the micro-nanoporous layer formed on a titanium-silver (Ti–Ag) alloy. The porous layer was formed by grit-blasting and anodic oxidation. The surface of the porous layer was rougher and more hydrophilic compared to a simple machined specimen and the expressions of bone-related genes were greater for cells grown on the porous layer compared to that of cells cultured on a control surface. Also the bone-to-plate contact rate in vivo test was significantly improved for porous layer plate compare to simple machined specimen (P < 0.05). The porous layer on Ti–Ag alloy enhanced the peri-implant bone formation at the early healing stage and it was believed that this porous layer on the Ti–Ag alloy will be suitable for dental implant applications.