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Background: nickel-titanium orthodontic arch wire due to its good super-elasticity, corrosion resistance and biocompatibility are widely used in the field of orthodontics. One of the side effects of orthodontic treatment tooth surface enamel demineralization, brackets appear around the chalk-colored plaque, caries or even seriously affect the appearance. Studies show that 50% of patients with fixed appliances in place around brackets enamel demineralization. Fluoride gel, the fluorine-containing reagent fluoride mouthwash can effectively prevent the use of enamel demineralization Objective: This study was designed to understand whether fluoride nickel-titanium orthodontic arch wires affect the mechanical properties and to observe the oral environment nickel-titanium orthodontic arch wire with pH, ??NaF concentration and changes in their working hours surface morphology, unloading force and microhardness changes. Methods: 0.016 inches in diameter thermally activated orthodontic arch wire end long straight section than 2cm in a sample of 72 samples were prepared. The experiment was based on the pH of artificial saliva, NaF concentration and immersion time samples were divided into control group and eight experimental groups, each containing eight samples. No control group experimental samples immersed in artificial saliva. Experimental groups: A set of samples at pH = 4 with NaF 0wt% artificial saliva soaked one day. Group B at pH = 4 samples containing NaF 0.05wt% of the artificial saliva soaked for 1 day. Group C, pH = 4 samples containing NaF 0wt% of the artificial saliva for 3 days. Group D pH = 4 samples containing NaF 0.05wt% of the artificial saliva for 3 days. Group E pH = 6 samples containing NaF 0wt% of the artificial saliva soaked for 1 day. Group F pH = 6 samples containing NaF 0.05wt% of the artificial saliva soaked for 1 day. Group G with pH = 6 samples NaF 0wt% of the artificial saliva for 3 days. H groups of samples at pH = 6 with NaF 0.05wt% of the artificial saliva for 3 days. Scanning electron microscopy (SEM), three-point bending behavior and microhardness test and control group observed after each experimental group after soaking the sample surface morphology, strength and microhardness unloading changed. Results: 1. Surface morphology: SEM results suggest that in the absence of NaF immersed in artificial saliva A, C, E, G group, the surface of the sample mostly pitting, and containing 0.05% NaF immersed in artificial saliva the B, D, F, H group, in addition to the sample surface pitting, but also shows a large area of ??general corrosion, pH = 4 immersed in artificial saliva A, B, C, D, respectively, the group of samples than immersion corrosion artificial saliva at pH = 6 in E, F, G, H group is more obvious. 2 Uninstall force: the experimental group, in addition to group E and F, the sample unloading force and blank group were significantly different. pH value of the sample unload force main factor (p lt; 0.001), pH value and the interaction between the immersion time, the sample can also affect the unload force (p lt; 0.001). NaF same concentration in artificial saliva sample after the same time the unloading force soaked with the increase of pH increases. 3 hardness: The results showed that the experimental group sample hardness compared with the control group was significantly increased (p lt; 0.05). pH value of the sample microhardness most important factor (p lt; 0.001), and NaF and the interactions between the soaking time, can also affect the hardness of the sample (p lt; 0.001). Immersed in artificial saliva containing the same concentration of NaF in the same time as the hardness of the sample with pH increases. Test results were statistically analyzed using SPSS16.0 software package. Three-point bending results and microhardness results are normally distributed, the average level as mean ± standard deviation (x ± S) said multiple sets of measurement data between groups were compared using univariate analysis of variance (one-way ANOVA) and LSD method. The impact of various factors such as pH, NaF concentration and immersion time and their interactions using multi-factor analysis of variance. Conclusion: The nickel-titanium arch wire surface corrosion with the decrease of pH increase, in the absence of NaF immersed in artificial saliva A, C, E, G group, the surface of the sample mostly pitting, and immersed in artificial containing NaF saliva, B, D, F, H group, in addition to the sample surface pitting, but also shows a large area of ??general corrosion. Under the same conditions, immersed in artificial saliva pH = 4 The A, B, C, D group of samples of corrosion than pH = 6 E, F, G, H sample group is more apparent. Nickel-titanium orthodontic arch wire hardness decreased with the increase of pH, which increases with pH unloading force becomes larger. pH value, NaF concentration and immersion time can be three nickel-titanium orthodontic arch wire on the performance impact, but the pH value is the main influencing factors, and in the acidic oral environment fluorine to form HF or NaF and destroy archwire the surface of the oxide film, but also affect the nickel-titanium orthodontic arch wires mechanical factor.
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