Cytotoxity Of Nickel Titanium Shape Memory Alloys Of Surface Oxidation

ObjectiveCurrently, nickel titanium shape memory alloy wires are widely used in the early stages of orthodontics. Nickel-titanium shape memory alloys are composed of nickel ions and titanium ions.For the temperature and mechanical stress,there is two different phases in the crystal structure of the alloys,namely,austenite and martensite. with its advantages such as shape memory effect in the field of medical metallic materials Nickel-titanium shape memory alloys show an absolute advantage, and become the most potential biological materials in orthodontic clinical. However, nickel-titanium shape memory alloy inevitably occur corrosion in the oral environment.Nickel-titanium shape memory alloy in the corrosion process will release nickel ions,which are found to have potential toxic effect to human. It is wide researched that preparation of nickel-titanium alloy by coating the surface to inhibit the precipitation of nickel ions, and its inhibition of precipitation of nickel ions has been confirmed by many experiments.The purpose of this study is to evaluate the cytotoxicity of nickel titanium shape memory alloy with surface oxidation.MethodsThe study of corrosion resistance and biocompatibility of nickel titanium shape memory alloy is mainly in vitro and in vivo. It is can be directly observed the corrosion of alloys in vitro. Materials were divided into oxidative materials group and non-oxidation group. L-929 cell line was chosen to assess the cytotoxicity of the two groups.The morphological observation and MTT test are choosed to evaluate cell toxicity of nickel-titanium shape memory alloys. Growth of L-929 cells was observed under inverted microscope. Optical density (OD) and relative growth rate (RGR) of cells cultured for 24 and 48 hours were detected using MTT test. 1. At 24 hours after culture, cells in the positive control group was abnormal; while, cells in the oxidation, non-oxidation, and blank control groups well adherent-grew. At 48 hours after culture, cytotoxicity was detected out in the positive control group; cells in the oxidation and blank control groups were normal and grew well. A few of cells in the non-oxidation group showed karyopyknosis.2. At 24 hours after culture, oxidation group, non-oxide group OD values were 0.926±.032,0.809±0.031.At 48 hours after culture, oxidation group, non-oxide group optical density values were 1.300±0.064,0.996±0.056.The OD value in the oxidation and non-oxidation groups was increased with the prolongation of culture time, and the value in the oxidation group was significantly higher than non-oxidation group.The oxidation group has The statistically significant difference of non-oxidation group (P< 0.05). According to grade 5 toxicity evaluation criteria,cytotoxicity was grade 0 in the oxidation group at 24 and 48 hours after culture. In addition, cytotoxicity was grade 0 at 24 hours after culture and grade 1 at 48 hours after culture in the non-oxidation group.ConclusionThe cytotoxicity of NiTi-SMA with surface oxidation is lower than the non-oxide alloy, which is coincidence with the requirement of the clinical application.