Potassium fluoride,anhydrous
           Potassium fluoride,extra pure
           Potassium fluoride,Granular
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           Hydrofluoric acid
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           Ammonium bifluoride
           Potassium Bifluoride
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           Sodium fluoride
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           Fluorosilicic Acid
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           Magnesium fluorosilicate
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The aim of this study was evaluate the effect of etching with different hydrofluoric acid (HF) concentrations on the shear bond strength between glazed feldspathic ceramic and metal brackets. Seventyfive blocks of glazed feldspathic ceramic were produced and randomly allocated to 5 groups:Ctrl- silane application only; HF1- HF1%+silane; HF3- HF3%+silane; HF5- HF5%+silane; HF10- HF10%+silane (standard procedures: etching for 1 min + washing + drying + silanization).

Traditionally, the method of treating the internal surface of the restoration with hydrofluoric acid (HF) followed silanization for the cementation of feldspathic restorations, has provided high bond strength with resin cements. The mechanism of adhesion in this context is known: HF selectively attacks the silica matrix, generating important micromorphological changes in the ceramic surface to create a micromechanical adhesion, while the silane provides a chemical bond between silica and the resinous material. However, when a glazed feldspathic ceramic is conditioned with HF, the context can become hostile, as this surface is rich in silicon dioxide (glass matrix), and therefore, etching of the ceramic surface is not preferably selective, because the whole surface is almost uniformly attacked. Thus, the micromorphological changes may not be effective in promoting sufficient mechanical microretention.

At the same time, it is known that 10%  hydrofluoric acid(HF) is extremely toxic to oral tissues and that it can promote weakening of the ceramic. Therefore, some published studies used different concentrations of HF in the surface conditioning of glazed feldspathic ceramic. Thus, in the context of Orthodontics, there is a clear dichotomy: the need to promote proper adhesion of orthodontic accessories on the ceramic surface and the requirement to prevent negative effects on the mechanical strength of the conditioned material. Accordingly, the study of different concentrations of HF becomes relevant in assessing the potential for micromorphological modification induced by acid application on the surface. This modification is important in creating micromechanical adhesion and it is importante to seek alternatives with lower acid concentrations, which are less harmful to the mechanical strength of the ceramic material, and, as the etching is intraoral, have a lower risk to the patient.