The Study On Preparation And Properties Of Nitrogen Doped TiO₂ Coated Composite Arch Wire

With the development and the improvement of society,the people more and more pay attention to the oral beauty.With the development and progress of materials science,the study of oral medicine materials is also deepening.In the field of orthodontics,the rach-wire materials is changing with each passing day.So far,several efficient and multi-functional orthodontic materials have been well developed.The significance of the improvement and research of orthodontic arch wire material is great for orthodontic treatment.How can the arch wire improve the efficiency of correction and shorten the course of orthodontic treatment?The research team carried out the study in 2002 who was guided by innovative thinking that combines the good qualities of the two arch wires to form a composite arch wire.Composite arch wire?CAW?is one of the most important orthodontic materials which was developed by Daqian Sun et al in 2011.CAW consists of nickel-titanium shape memory alloy?TiNi SMA?,stainless steel?SS?arch wire which are laser-welded via copper inter layer.CAW is a new type of orthodontic arch wire.At present,NiTi and SS arch wires are widely used in the different stages of orthodontic treatment.In the process of orthodontic treatment,the nickel titanium wire is used in early stage.Align and level dislocated teeth by using nickel titanium wire fast memory function.In the later stage,the rigidity of the stainless steel wire is used to strengthen the anchorage and stabilize the position of the teeth so as to prevent the unfavorable movement.In this way,the orthodontic treatment period is prolonged,which decreases the efficiency of the orthodontic treatment.Especially,the different stiffness and performance of the arch wires are needed in the different parts and different periods of the dental arch teeth.Thus,it cannot meet the clinical needs by using a single arch wire,and CAW can solve this problem.CAW can move the teeth with nickel titanium arch wires and provide anchorage with stainless steel wire.The power of the soft nickel titanium arch wires are directly used on the dislocation tooth to move tooth effectively,while the rigidity of stainless steel wires are used to strengthen anchorage teeth stability and prevent the negative moving.Then,CAW combines the advantages of each material to correct the malposition of the tooth which can improve the treatment efficiency and shorten the course of treatment.The selection of materials for dental applications depends upon a number of factors such as corrosion behavior,mechanical properties,biocompatibility and aesthetic value.The corrosion behavior of metallic materials is usually the most important property,because biocompatibility and cytotoxicity are dependent on the products of the corrosion process.It has been reported that 46%of the orthodontic patients will occur demineralization within 12 months who are treated with fixed appliance.The main reason of demineralization during orthodontic treatment with fixed appliance is attached dental plaque.It has been reported that after using fixed appliance for 1 to 3 weeks,the proportion of streptococci mutans in dental plaque increased one time.Note that the difference is significant,and the corrosion of the metals in which played an important role,which had been found to induce specific changes in the oral environment,such as decreasing pH and increasing dental plaque accumulation.The increase in the number of lactobacilli and streptococcus mutans will decrease the pH value in the mouth,which is contributed to tooth demineralization when pathological changes occurred.Traditional preventive methods of enamel demineralization include proper tooth brushing,fluoride rinse or varnishes,a fluoride-releasing bonding system,acidulated phosphate fluoride?APF?foam or gel,and using acid etching area.However,these approaches require good cooperation with orthodontic patients,and the drug concentration is difficult to maintain.The complicated procedures would make clinical treatment more difficult.The composite wire does have great advantages in orthodontic treatment,but the arch wire by a variety of different metal materials,The nickel titanium part and the stainless steel part,especially the middle copper interlayer in the oral environment,there will be precipitation of metal ions,and the interaction between the three will aggravate the arch wire its corrosion,reduce its service life and increase oral health hazards,but also will cause the precipitation of copper ions harmful.The main content of this research is the corrosion of CAW and how to modify it.In our study the saliva in oral cavity is the basic corrosion environment which we simulated for studying corrosion resistance and antibacterial properties of CAW in vitro.Radio frequency?RF?magnetron sputtering is an effective method due to its inherent multi functionality,uniform surface coverage and low-temperature deposition.The main advantage of magnetron sputtering is able to deposit inorganic nanoparticle thin films with controllable size and shape by tuning preparation parameters.Therefore,in this study,in order to further improve the corrosion resistance of composite archwire and antibacterial activity,we use the method of magnetron sputtering to deposite titanium dioxide and nitrogen doped TiO₂ thin films onto the surface of the sample.This paper takes this as the starting point,the composite arch wire surface using nitrogen doped titania coating,then the samples were exposed to artificial saliva,the microstructure,corrosion resistance,photocatalytic activity,antibacterial properties and biological safety properties of the films were studied comprehensively and systematically.Firstly,the sample of composite arch wire was prepared,and the laser welding technique was used to weld the copper interlayer to the two section of nickel titanium bow wire and stainless steel bow wire.The elemental distribution was observed by energy dispersive spectrometer?EDS?,and the results showed that the three materials were completely melted at the welded joint.The sample films were covered on the composite bow wire by equal frequency magnetron sputtering.The films were pure titanium dioxide when the protective gas was argon completely,and when the protection gas of argon and nitrogen is 30:1,the prepared film is nitrogen doped TiO₂film.X ray photoelectron spectroscopy?XPS?tests showed that nitrogen was successfully doped into the TiO₂ film.Then the photocatalysis of CAW was tested.The sample was enclosed in a closed glass reactor with glyoxal for two hours in visible light.The decomposition rate of glyoxal was detected by gas chromatography.It was found that the rate of degradation of acetaldehyde by nitrogen doped Ti O₂ film was 5.2 times of that of pure TiO₂ film.In corrosion test,human saliva was used as electrolyte,CAW and coated sample were used as working electrode,the corrosion resistance of different samples was evaluated by electrochemical polarization curve and electrochemical impedance spectroscopy.The test shows that the nitrogen doped TiO₂ films significantly improved corrosion resistance in simulated artificial saliva medium,and nitrogen doped TiO₂ thin films than un-doped films with a better corrosion resistance.After corrosion,the corrosion of the composite wires appeared obviously,while the surface of coated CAW did not appear obvious corrosion.In the antibacterial experiment,the common Streptococcus mutans in the oral cavity was used as the antibacterial experimental object,and the sterilized samples were cultured in the bacterial culture medium and cultured under visible light irradiation.The control group showed no antibacterial,the nitrogen doped Ti O₂ films showed obvious antibacterial properties in comparison with un-doped group,antibacterial rate reached 87.2%,the un-doped group was only 5.9%.Nitrogen doped titanium dioxide film has very strong antibacterial effect.Finally,the composite arch filament cytotoxicity test was carried out.The mouse fibroblast L929 was used as the experimental cell,and the cell culture was carried out by using 72 hours leaching solution.Cell counts were performed at 24h,72h,and120h,respectively,the results show that the nitrogen doped TiO₂ group has the most cell counting at all time periods,which shows that the CAW modified by nitrogen doped TiO₂ film has high biological safety.Therefore,the nitrogen doped TiO₂ coating can comprehensively improve the performance of CAW,more complex clinical standards also enable composite bows to meet clinical needs earlier and benefit patients.