Preparation, Properties And Biocompatibility Study Of Orthodontic Brackets Coated With TiO_2-x N_x Thin Film

Malocclusion is one of the common oral diseases while fixed orthodontic technology is the dominating treatment method. Brackets are the core devices of fixed orthodontic technology, and penetrating the whole process of orthodontic treatment. Nevertheless, white spot lesions, or enamel demineralization around brackets are the primary complication. Studies showed that the incidence of such disease ranges from2%to96%during the treatment. In horizontal approaches16.23%～97%of orthodontic patients had enamel demineralization after orthodontic treatment. Currently, to prevent the occurrence of enamel demineralization, constructing patients how to reduce dental plaque is the most commonly used method. Formly, prevention approach against enamel demineralization during fixed orthodontic treatment, such as, fluoride, antibacterial adhesives, laser irradiation, Chinese Traditional Medicine and different ways of acid etching were used. However, there are certain deficiencies in the methods above which depends on the cooperation of patients as well as drug concentration.In this study, RF magnetron sputtering method was used to prepare TiO2-xNx thin film on the surface of stainless steel metal bracket, and18groups of samples were made according to the experiment parameters. The crystal structure, surface morphology were characterized by XRD, SEM; photocatalytic performance were tested by photocatalytic analysis. The parameters of the target thin film samples were set as follows:the sputtering temperature was set as300℃, and the time was set as180min, ratio of Ar/N was30:1, annealing temperature was at450℃. The thickness and element contents were also analyzed. It was found that TiO2-xNx thin film was well-distributed and compact, and the thickness was about500nm, and of high crystallinity. The grain size was around30nm. Demonstrating the thin film was anatase phase. The ratio of nitrogen content was4.24%.The results showed the film has good adhesion strength; the surface roughness and the coefficient of static friction and coefficient of kinetic friction of orthodontic brackets coated with TiO2-xNx thin film were lower than orthodontic brackets without TiO2-xNx which tested by multifunctional material surface tester, atomic force microscope and14FW reciprocating friction tester respectively. Scanning electron microscopy and UMT-2MT friction-abrasion testing machine was used to study frictional wear properties of the TiO2-xNx films. It was found that the TiO2-xNx films revealed apparent anti-friction under dry friction and two lubrication conditions, that is to say, the TiO2-xNx films on the surface of stainless steel brackets had good wear resistance. TiO2-xNx film brackets had good corrosion resistance and film stability which were analysed by studying the ion release ratio of the samples. Shimadzu electronic universal testing machine was used to study the adhesive strength of TiO2-xNx film to brackets, the result indicated the value of adhesive strength was greater than8Mp. The strength could meet the requirements of orthodontic treatment. The antibacterial performance of the samples under visble light was conducted by colony counting method. The adhesive ability was tested by SEM. And the results showd that the antibacterial effects of TiO2-xNx against the four main pathogenic bacterium(streptococcus mutans, lactobacillus, actinomuces viscosus, Candida albicans) in oral environment. The antibacterial ratio were95.16%,91.00%,69.44%and98.86%in order. Meanwhile, streptococcus mutans adhered to the surface of TiO2-xNx thin film was less than that of common MBT brackets.Biocompatibility study of TiO2-xNx thin film brackets showed that the cytotoxicity of the samples was on grade0. Compared with control group, the percentage of cell proliferation showed no statistical difference(p>0.05). The SEM photos showed the cells grew well on the surface of the films. The nulei was bright yellow-green fluorescent, cytoplasm was green fluorescent on the surface of the films under fluorescence microscope. Animal research showed TiO2-xNx brackets had good biocompatibility with no oral mucosa irritation response, short-term systematic toxicity, hemolysis and genotoxicity.The above research results demonstrating TiO2-xNx thin film has great material performance, antibacterial ability and biocompatibility, would be able to be a effective method to prevent enamel demineralization during the whole process of orthodontic treatment.