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Hydrofluoric acid is applied to glazed feldspathic ceramic surfaces to increase micromechanical retention, and to prepare the surface prior to silane application. The results of this study showed that the HF concentrations tested did not significantly influence the obtained shear bond strength of metal brackets adhered to glazed feldspathic ceramic surfaces. This is in agreement with the findings of Trakyaliet al.,which compared HF concentrations of 5% and 9.6%. 10% Hydrofluoric acid  did not show the highest mean shear bond strength, and, as such, the tested hypothesis was rejected.

Hydrofluoric acid changes the topography of glazed feldspathic ceramic surfaces. The SEM images show that HF dissolves the glass matrix of the glaze layer, creating pits on the surface, and that the changes created by applying 1%, 3% and 5% HF does not appear to be regular. However, we note that the HF does not uniformly attack the glazed ceramic surface. This could be explained by the lack of standardization of the glaze layer thickness, amount of powder and liquid in the glaze mass. Low shear bond strengths were found in this study (1.1-4.1 MPa); lower than those reported in previous studies (6-10 MPa).

10% Hydrofluoric acid  showed the lowest shear bond strength and this can be explained by the fact that 10% HF is a strong and aggressive acid, and created deep pores in the ceramic surface that couldn’t be filled by the adhesive, weakening the structure. An ARI score of 0 was given, as no cohesive failure was observed after debonding. It showing that the measured shear bond strength is representative of adhesion between the ceramic and adhesive system. The contact angles decreased significantly after the application of HF, as the acid increases the surface free energy of the substrate and the wettability of the adherent on the ceramic surface, increasing the potential of adhesion. Contact angle findings were not reflected in the shear bond strength results.