Materials and methods: Two types of plastic brackets were used (Silicon and Spirit). Both of them were exposed to three fluoride solutions (APF, NaF and SnF2). Each type of bracket was studied before and after cyclic immersion (1 min each time, 10 times) in each F- solution by (a) ATR FTIR spectroscopy; (b) scanning electron microscopy and X-ray energy dispersive microanalysis (SEM/EDS); and (c) Vickers hardness measurements. Hardness data were analyzed with two-way ANOVA and Tukey test at the .05 level of significance with bracket and fluoride solution as predictors.
Results: ATR FTIR showed that both brackets have similar organic phase (polycarbonate). After APF treatment an increased contribution of -OH peaks at 3200 cm-1 (str) and 1640 cm-1 (b) was observed in both brackets. SEM revealed that APF and NaF had prominent effects on the morphology and surface structure of brackets with projections of reinforcing fibers, and surface deterioration. EDS showed evidence of Al, Si, Ca, Mg, K, assigned to reinforcing glass fiber constituents. No difference was found among the three treatments and two bracket type in hardness, which ranged in the order of 20 VHN.
Conclusion: Repeated exposure of plastic aesthetic brackets to fluoride solutions may have a pronounced effect on structure and morphology, however no hardness changes are observed.