| Fixed appliance which is good for retention, anchorage, easy to apply various types of orthodontic force, accurately controlling the tooth of3D moving direction is widely used in orthodontic clinic. The bracket is the important device for orthodontic technique which makes patients difficult to maintain good oral hygiene, soft dirt and food residue easy to stay, plaque likely accumulate in surrounding of the bracket providing an ideal environment to retention because of the complex surface structure of the bracket, thus causing the occurrence of complications such as demineralization of enamel,dental caries and gingivitis. Studies have shown that prevalence of demineralization has ranged as high as50%to80%in patients with fixed orthodontic treatment. Plaque formation is the main causes of demineralization, therefore plaque control is key to the prevention of enamel demineralization. Because the conventional brushing can only remove40%-60%of plaque, and using mouthwash in order to maintain good oral hygiene as an auxiliary method of mechanical plaque control has certain significance, Mouthwash can penetrate into various parts of the mouth, especially for the free gingiva edge and the tooth adjacent surface where the toothbrush is hard to reach, producing a good cleaning effect. Research shows, mouthwash can remove bacteria from the teeth adjacent surface44%amount, to cause halitosis disease90%of the bacteria effectively, and can decrease56%of the plaque, as well as to prevent and delay the onset of gingivitis.TiO2as a kind of inorganic photocatalytic antibacterial agent, has good resistance to physiological corrosive, self-cleaning and antibacterial effect and biological safety,and also in terms of pollutant treatment and energy conversion is of great application value. Chun maked the TiO2film coated on surface of the orthodontic wire, with the ultraviolet excitation it can effectively reduce the adhesion of Streptococcus. The formation of TiO2film in orthodontic bracket surface sputtering by Shah AG, can reduce the adhesion and limit the growth of Lactobacillus under the effect of ultraviolet light. But the visible light photocatalytic efficiency of TiO2is lower, the1986Sato found that the incorporation of nitrogen can make TiO2have visible light activity, also in2001Asahi R reported that nitrogen-doped TiO2had excellent visible light activity. Li Na and other scholars have made orthodontic brackets coated on the nitrogen-doped TiO2films, and their basic properties have been studied. Zhang Yingjie preliminary confirmed that the brackets coated with nitrogen-doped TiO2film had good biocompatibility.In the orthodontic treatment process, the bracket which is throughout the treatment for the whole, exists in the disease population, and has the friction between the arch wire will be required higher biological safety. However, stainless steel metal bracket under certain conditions will rust, and temperature, oxidant, PH value change, can make stainless steel corrosion resistance decreased and the release more bad metal ions. However stainless steel contains certain components of nickel,2.2%women and about11.1%of the men have an allergic reaction to the nickel. Chlorhexidine mouthwash will aggravate the stainless steel metal bracket corrosion, releasing harmful metal ions more.Based on the researchs about stainless steel metal bracket, this research makes the surface of metal brackets coated on TiO2-xNx thin films which have visible light photocatalytic activity by RF magnetron sputtering method, and studies their biological friction wear and corrosion resistance in order to provide a theoretical basis for the clinical. This study is divided into three parts:1. Preparation and characterization of TiO2-xNxthin film samplesDomestic metal bracket materials samples (prepared into20mm×10mm×1mm)and metal brackets together are prepared of TiO2-xNx films on their surface by using JZCK-580high vacuum magnetron sputtering machine, then the prepared TiO2-xNxthin film samples are annealing for2h at450℃in the high temperature box resistance furnace, the structure and the surface morphology of the films are analyzed by X ray diffraction and scanning electron microscope. The results show that the TiO2-xNx thin films surface appear red and green; TiO2-xNxthin films are an anatase and nanometer structure; TiO2-xNx films are uniform distribution and dense structure.2.Study on friction and wear properties of TiO2-xNx thin film bracketTiO2-xNxthin film bracket substrates (prepared into20mm×10mm×1mm) and stainless steel bracket substrates are separately proceeded under the dry friction and lubrication medium of friction test by using a UMT-2MT type of the United States of America CETR company production. All experimental samples are tested3times in each experimental condition.The lubricating medium use artificial saliva and the Hank’s solution which is similar to body fluid and physicochemical properties. At the start of the experiment, the lubricating medium is dripped on the surface of the test sample, the coefficient of friction is recorded by the instrument automatically and given by the data processing software. The worn surface morphology of the samples is observed by scanning electron microscopy.The results show that, the friction coefficients of three kinds of experimental conditions in TiO2-xNxfilm group are less than stainless steel metal group with significant statistical difference(p<0.001);SEM photos of stainless steel show, the worn surfaces are serious deformation, and wear scar bottom exists large area exfoliative forming deep furrows and appears obvious wear tear. SEM photos of TiO2.xNx thin film samples show, the worn surface is smooth, and appears no abrasive and furrow abrasion, only a small amount of wear. Due to the TiO2-xNxfilm is composed of nano particles, uniform density, good toughness, not easy to brittle fracture, thus showing good anti-wear property.3.Study on the corrosion resistance of TiO2-xNx thin film bracketTiO2-xNx thin film brackets and metal brackets are respectively arranged on three kinds of mouthwash in airtight container glasses, detecting in the three kinds of soaking solution of nickel, chromium, iron, titanium ion concentration after45days by Hitachi180-80atomic absorption spectrometer, TiO2-xNxthin films are observed by using scanning electron microscope; using the CHI electrochemical detection to test the polarization curve, corrosion potential (Ecorr) and corrosion current of TiO2-xNx thin film brackets and metal brackets, calculating the corrosion current density (Icorr). The results show that, ion precipitation levels of TiO2-xNx film thin brackets in the three kinds of mouthwash are lower than the ion daily diet intake level of human, and the films are complete; the corrosion potential of TiO2-xNx thin film brackets is larger and the corrosion current density is smaller comparing with metal brackets, so corrosion resistance of TiO2-xNxthin film brackets is superior to the metal brackets.Conclusion:this study is successful in coating nanometer TiO2-xNx thin film on the surface of metal brackets which is uniform distribution and dense structure; Biological friction and wear experiments show that the properties of TiO2-xNx thin films have higher friction wear resistance and a steady structure;corrosion experiments show that the TiO2-xNx thin film can improve the corrosion resistance of metal brackets,reflect the good biological safety, and then provide a theoretical basis for clinical using. |
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