Influence Of Different PH And Time On Cytotoxicity Of Nickel-titanium Orthodontic Wires In Vitro Experiment

Objective:This experiment was designed to investigate the influence of different pH andtime on cytotoxicity of heat-active Nickel-titanium orthodontic wires in simulate oralcircumstance,and which would provide some reference for its clinical application.Methods:1.The specimens was obtained by cutting2cm segments from two terminals ofthe diameter of0.014inches heat-active nickel-titanium wires,which was maintainedin artificial salive,in1day,7days,14days and28days respectively,which pH were4.0,5.0,6.8,8.0.In addition to the experimental group, set up three following controlgroups,Group C is negative control group, which samples add in100ulRPMI-1640culture medium without soaking.Group D is positive control group, the sampleswithout soaking, only add6.4%phenol solution.E is zero set group, without sample,add100ul1640medium.2. This experiment was designed to draw cell growth curve by cultivating the3t3cells,which determine the most suitable concentration of test cells,and3T3cells werecultivated with each extract liquids of all groups at CO2constant temperatureincubator in48hours,then, MTT colorimetric method was used to measure opticaldensity value of each group, and evaluate the rank of cytotoxicity.according torelative growth rate (RGB) of cells.Result:1.The optimal3T3cell concentration for this experiment is at5.98×104/ml.2.At pH were4.0,5.0,5.0,6.8,8.0respectively,the optical density of each groupwith soaking time have statistically significant change（P<0.01）,which is positivelyrelated with immersion time and the absorbance value decrease prompted cytotoxicitywas increased.3.At pH were4.0and5.0, the cytotoxicity of each group was2grade.4.the toxic levels is0grade in1day and7days groups and is1grade in14dayand28days groups,which meet the national standard of medical devices. Conclusion:1.The the cytotoxicity of nickel titanium arch is positively related withimmersion time and negatively with pH value size.2. Each cell toxicity level of0~2grade,which conform to the medical devicesafety standards; But in pH4.0and pH5.0, there are multiple sets of cytotoxic levelsclose to level3, therefore, it suggested that the clinical use of nickel titanium archwire treatment stage should avoid strongly acidic environment.