In Vitro Biocompatibility Of Orthodontic Brackets Coated With TiO_2-xN_x Film

The oral is a quite complicated environment, when wear onto the teeth, the use of brackets and archwire creates a challenging environment to providing excellent oral hygiene and an increased surface area for plaque adherence. These appliances also interfere with the natural cleansing action of oral, leading to an increased risk for caries on dental surfaces that are not usually the target of carious attacks.Because plaque accumulation around brackets is the main cause of WSLs, so the control of plaque attaching is the key to prevention of WSLs. Our group successfully prepared improving brackets coated with TiO2-xNx films by RF magnetron sputtering method, which have good antibacterial properties on test bacteria under visible light. Although the films have achieved good results in vitro antibacterial experiments, but the safety evaluation before clinical application is also particularly important. Currently the safety evaluation studies on TiO2-xNx films are rarely reported. Therefore, this research was conducted in vitro biocompatibility to explore the influence of nitrogen content and thickness of TiO2-xNx films on the L929 mouse fibroblasts cells’adhesion, proliferation and apoptosis, so as to provide the safety and reliable basis for clinical application of TiO2-xNx films brackets.Objective To assess improving brackets’biosafety which were coated with the films of TiO2-xNx, and to explore the effects of nitrogen-doped content and thickness on biosafety deeply.Methods 1. TiO2-xNx films were manufactured on the surfaces of 3B brackets by the method of RF magnetron sputtering through changing the preparation parameters with different nitrogen-doped content and thickness, and physical relevant characterizations were test.2. L929 cells were used to evaluate the biocompatibility of TiO2-xNx film of orthodontic brackets by the methods of cell adhesion, MTT/LDH assay and fluorescence count.Results 1. We have successfully prepared TiO2-xNx film on the surfaces of 3B brackets sample made in China by RF magnetron sputtering with different nitrogen-doped content and thickness.2. The L929 cells adhered and spread well on the surface of these thin films and the control group; Although the cell relative proliferation rates of the experiment group of nitrogen content, thickness and control one were more than 80%, and the level of TiO2-xNx films’ cytotoxicity was grade 0, there were significantly statistical differences between experimental and control groups (P<0.05). As nitrogen content increasing, RGR decreased, and as the increasing of the films’ thickness, the RGR increased; The results showed that LDH activity was positively correlated with the films’ nitrogen content, and it was negatively correlated with films’ thickness; The results of cell counting method are consistent with the results determined by MTT and LDH.Conclusion Our research group has successfully prepared TiO2-xNx films on the surfaces of 3B brackets sample by RF magnetron sputtering with different nitrogen-doped content and thickness, which were anatase phase, nanometer. Grain size was uniform, dense. The results showed that the L929 cells adhered and spread well on the surface of these thin films and the control group by the direct contact with the culture test; the RGR of all groups were more than 80%; the LDH activity was lower, and the improving brackets’ cytotoxicity level was grade 0. Results showed that these films have good biocompatibility. The nitrogen content and film thickness are relevant factors on the biosafety of improving brackets.