Potassium fluoride,anhydrous
           Potassium fluoride,extra pure
           Potassium fluoride,Granular
           Silicon Dioxide
           Hydrofluoric acid
           Synthetic Cryolite
           Potassium Fluoaluminate
           Ammonium bifluoride
           Potassium Bifluoride
           Aluminium fluoride
           Sodium fluoride
           Potassium Fluorosilicate
           Fluorosilicic Acid
           Sodium silicofluoride
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           Magnesium fluorosilicate
           Barium Fluoride
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In this study,Hydrofluoric acid was used for only 1 min on the glazed feldspathic ceramic, following the manufacturer’s instructions, and the exposure time did not appear to be enough to create adequate micromechanical retention. There is no consensus about HF action time on glazed ceramics in the literature; about 1-4 min application would be advocated. 

Increasing the time of Hydrofluoric acid application on the ceramic surface could be an alternative to enhance adherence and to increase the shear bond strength, however, with an increase in etching time, the results demonstrated a decrease in the mechanical strength of the ceramic material. Addison et al.studied the impact of HF surface etching on flexural strength of feldspathic ceramics and they observed a significant strength reduction with increasing etching time. 

Also, owing to the high toxicity of Hydrofluoric acid, there is difficulty in managing this acid in the oral cavity. No studies were found on the hazardous effects due to HF exposure in the dental literature, but in the previous study that HF has a hightissue penetration power, which may cause irritation, burns, haemorrhages, necrosis, and death, depending on the tissue involved, and acid quantity and concentration. There were several concentrations of HF in this study, as follows,HF:1%,HF:3%,HF:5% and HF 10%, these diffferent concentration of Hydrofluoric acid were applied for 1minute on glazed surface.The hypothesis tested that 10% Hydrofluoric acid promotes the highest shear bond strength was rejected. The different concentrations of hydrofluoric acid did not significantly influence the shear bond strength of metal brackets adhered to glazed feldspathic ceramic surfaces. In terms of  bond mechanical tests, the current investigation used the shear test, which presents a main limitation: non-homogeneous stress distribution at the interfaces. Even with this limitation, the observed failures, as previously mentioned, were adhesive failures at the resin-ceramic interface, which means the real shear bond strength was evaluated by this study.