Effect of Sodium Fluoride Solutions on Brackets Composition and Surface

Objectives: To compare the compositional and surface changes of two types of orthodontic brackets in different pH sodium fluoride solutions.
Methods: Experimental in vitro study. Protocol was reviewed and approved by IRB. 60 brackets were distributed in two groups of thirty specimens each, depending on the material tested: stainless steel (Gemini™, 3M Unitek, USA) and aluminum oxide (Clarity™, 3M Unitek, USA). Each group was randomly divided into three subgroups (n=10). Subgroup 1: control group (no immersed), subgroup 2: brackets immersed in an acid solution of artificial saliva modified with 0.02% sodium fluoride and a buffer solution (pH 4) and subgroup 3: brackets immersed in a basic solution of artificial saliva modified with 0.02% sodium fluoride buffer solution (pH 7). Brackets remained immersed for 21 days under static conditions at a constant temperature of 37°C. Then, chemical composition and surface characterization were evaluated by spectrometry with an x-ray fluorescence spectrometer (Geminis, EDAX-DX4, USA) and a scanning electron microscope (XL30, Philips, Holland). Statistical analysis was performed using Bonferroni, Shapiro Wilk, Levene, one way ANOVA and Tukey tests.
Results: Electrochemical analysis of stainless steel group showed statistical significant differences between subgroups when Nickel and Iron percentages were compared (p<0.05). Control subgroups reported the highest percentages, followed by pH 4 and pH 7 subgroups. No statistical differences were observed when Chrome percentages were compared (p>0.05). Aluminum oxide group showed no statistical significant differences when oxygen and aluminum percentages were compared between the three subgroups (p>0.05). Scanning electron microscopy analyses reported the presence of irregular surfaces in both types of no immersed brackets. However, after being immersed in pH4 and pH7 test solutions, these alterations became more pronounced and evident.
Conclusions: Sodium fluoride modified solutions generated pitting and intergranular corrosion at stainless steel brackets and microstructural surface alterations at aluminum oxide brackets without chemical degradation.