Influence Of Fluoride On Cytotoxicity Of Nickel-titanium Orthodontic Arch Wires In Vitro Study

Objective:This study was designed to observe the cytotoxicity changing of nickel-titanium orthodontic arch wires immersed by artificial saliva of different concentration of fluoride, and evaluate the influence of fluoride on biocompatibility of nickel-titanium orthodontic arch wires, so as to provide some reference for the efficient and safe clinical application of fluoride in orthodontic treatment.Methods:1. Prepared the artificial saliva and three kinds of artificial salive with different NaF concentration (0.05%,0.10%,0.20%). The specimens were collected by cutting out30mm section from the diameter of0.018inches domestic nickel-titanium wires. All the80specimens were randomly divided into4groups, each group contains20specimens. Then put them into the artificial saliva kept at37℃for28days. Removed the first three sets of samples into three kinds of artificial salive with different NaF concentration (0.05%,0.10%,0.20%) in turn for three minutes, then taken them out and washed them with distilled water. Finally sucked with filter paper and put back to original artificial saliva. This process should be repeated three times per day. The fourth group was the control group which without immersion in fluoride solution.2. Taken out4groups of samples and immersed in the RPMI-1640culture medium to produce4kinds of extract liquid. Then L929mouse fibroblast cells were cultivated with the four extract liquids mentioned above, negative control liquid and positive control liquid, respectively. After48hours, MTT assay was used to test OD value of each group, calculate relative growth rate (RGB) and thus evaluate the rank of cytotoxicity. Apart from these, flow cytometry and Annexin V-FITC/PI double staining method were utilized to identify and distinguish cells in different statuses, which include viable cells, early apoptotic cells and late apoptotic or dead cells. The distributions of cells in each group were compared and cell distribution scatter diagrams were generated. Result:1. MTT assay showed the cytotoxicity of the control group (without immersion in fluoride solution) ranked the level of1; The two groups of arch wires treated by0.05%and0.10%NaF solutions ranked the level of1; The group of arch wires treated by0.20%NaF solutions ranked the level of2; the positive control group ranked the level of4.2. Cell distribution scatter diagrams demonstrated that cells were mainly consisited of viable cells in negative control group whereas early apoptic cells and viable cells made up the main cell portions in the two groups which were treated by0.05%and0.10%NaF solutions. However, in the group which were treated by0.20%NaF solutions, the distribution of cells changed significantly, where early apoptic cells and late apoptic cells or dead cells made up the major proportion of the cells.Conclusion:1. The cytotoxity of NiTi arch wires can be influenced by fluoride, and the effect was possibly concerned with the concentration of fluoride. When the concentration of fluoride was0.05%and0.10%, the fluoride has no effect on the cytotoxity of the NiTi wires. When the concentration of fluoride was0.20%, the fluoride can increase the cytotoxity of the NiTi wires.2. We suggest the patient who is in the process of taking orthodontic appliance with NiTi wires should avoid using fluoride or using fluoride with low concentration.