| With the improvement of living, orthodontic treatment is becoming more and more popular in the majority of the people in our country. Facing all kinds of malocclusions, both the orthodontic materials and orthodontic technology are constantly changing. Fixed appliance technology is currently the most mainstream treatment methods.Metal alloys were used as the main material of fixed appliance. During orthodontic treatment with fixed appliance technology, the stainless steel brackets (core devices of fixed appliance) needed to be bonded to the tooth surface and bear the force that controlling the three-dimensional movement of the teeth, during the whole orthodontic treatment period, which is normally as long as 18 months. While, On the one hand, due to the complex structures of these brackets itself, plaque accumulation is vulnerable around the brackets, and then enamel demineralization, gingivitis and other complications are usually occurred around these brackets. On the other hand, all the oral temperature, pH, ionic composition of saliva and microbiological composition can change from time to time, which may increase the complexity of the oral environment. Stainless steel metal brackets immersed in the weak electrolyte environment for a long time as long as 18 months, are easily to be eroded in varying degrees. At present, most of the stainless steel brackets contain nickel or chromium ions in different proportions. When the surface of stainless steel metal brackets were eroded, nickel, chromium and other ions may release and accumulate in the body. These toxic irons for a Jong time direct contacting with the tissue cells, are easily to make human sensitization, mutagenic, causing cell toxicity and other adverse reactions. What’s more, the poor mechanical properties of the eroded orthodontic appliances can also not be ignored.In order to reduce the complication, such as enamel demineralization and gingivitis, enhance corrosion resistance of the fixed orthodontic appliance in the oral cavity environment, reduce the harm caused by corrosion and meet the requirements of mechanical performance of orthodontic treatment during the fixed orthodontic treatment, on the one hand, application of titanium and compounds is becoming more and more popular for their good biological compatibility and chemical stability; on the other hand, many advanced manufacturing technologies are introduced to the field of dental materials in order to enhance or improve the surface properties of the existing materials. These manufacturing technologies including all kinds of surface coating technology and various surface treatment technology. But up to now, the metal alloy materials that being applied in orthodontic clinical, can’t be maintaining good physical mechanical properties, be exempt from enamel demineralization and other complications caused by plaque accumulation and be exempt from corrosion and the damage caused by the ion precipitation, at the same time during fixed orthodontic treatment. Based on the research of Shah AG, Asahi and other scholars, in our previous research N-doped TiO2 thin film was successfully prepared on the surface of domestic stainless steel metal bracket by magnetron sputtering technology, experiments confirm that N-doped TiO2 thin film has good abrasion resistance, good mechanical properties; and N-doped TiO2 thin film has highly antibacterial activity under visible light irradiation, which can be beneficial to antibacterial, anti pathogenic bacteria adhesion, and then reducing the incidence of enamel demineralization and gingivitis; while the corrosion resistance of N-doped TiO2 thin film still needs further testing.In present study, we prepared N-doped TiO2 films of different thickness (N-doped TiO2 60mins, N-doped TiO2-120mins, N-doped TiO2-180mins) on the surface of stainless steel metal substrate by magnetron sputtering film forming technology through changing the experiments of time. The phase structure, surface morphology were characterized. The electrochemical corrosion behavior of N-doped TiO2 films were tested in two simulate oral solution (the pH 6.75 artificial saliva and the 1.23% APF solution), as well as the behavior of nickel, chromium ion release and inhibition after immersion were detected, aiming at comprehensive evaluation of corrosion resistance that N-doped TiO2 film can bear in the simulated oral solution, and aiming at providing the experimental basis for the clinic use of N-doped TiO2 film brackets.Results of this research show that N-doped TiO2 thin films were prepared successfully by magnetron sputtering film forming technology. The films are uniform and dense, character of anatase structure, nanometer, of which N-doped TiO2-120mins group is the most uniform and dense, free of crack defects. In both the pH 6.75 artificial saliva and 1.23% APF solution (pH 3.5, the fluorine content is 0.20%) electrochemical test were done, contrasting with the uncoated group, N-doped TiO2 thin films group showed better corrosion resistance, N-doped TiO2-120mins was the best (p<0.05). In both the pH 6.75 artificial saliva and 1.23% APF solution (pH 3.5, the fluorine content is 0.20%) ion release level after immersion were detected, contrasting with the uncoated group, N-doped TiO2 films group showed less nickel,chromium ion emissions (p<0.05), N-doped group TiO2-120mins group was the least (p<0.05). Nickel, chromium ion release level of N-doped TiO2 thin films is far less than the WHO recommended daily intake. Conclusion can be drawn through this research:in the two simulated oral solution environments, N-doped TiO2 film can improve the corrosion resistance of stainless steel, and decrease the nickel and chromium ion release amount of stainless steel, which is beneficial for clinic use. |
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