Effect of fluoride solutions on the structure and hardness of plastic brackets.

Aim: To investigate the surface morphology, structure, molecular and elemental composition, and hardness of plastic brackets exposed to fluoride solutions.

Methods: Two types of plastic brackets (Silkon Plus and SpiritMB) were exposed to three fluoride solutions 10 times for 1 minute each and then subjected to attenuated total relectance-Fournier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy (SEM), x-ray energy dispersive microanalysis (EDS), and Vickers hardness (HV) testing. Hardness data were analyzed via two-way ANOVA and Tukey tests at the .05 level of significance with brackets and fluoride solution as predictors.

Results: ATR-FTIR spectroscopy showed that both bracket types consisted of polycarbonate. After treatment with acidulated phosphate fluoride, an increased contribution of -OH peaks at 3,200 cm-1(stretching [str]) and 1,640 cm-1 (a type of vibration [b]) was observed in both brackets. SEM revealed that the acidulated phosphate fluoride solution had a strong effect on the morphology and surface structure of the two brackets; a general deterioration with projections of the reinforcing fibers was observed. EDS showed evidence of aluminum, calcium, silicon, magnesium, and titanium, which could be attributed to the reinforcing glass fiber constituents. Hardness ranged in the order of 20 HV with no difference among the two bracket types and the three fluoride exposures.

Conclusion: Repeated exposure of plastic brackets to fluoride solutions has a pronounced effect on their structure and morphology, but not their hardness.