A low-toxicity ammonium hydrogen fluoride-based etchant for bonding pretreatment of silica-based CAD-CAM materials

This study aimed to develop a low-toxicity etchant for bonding pretreatment of silica-based CAD-CAM materials. An experimental etchant was prepared by combining ammonium hydrogen fluoride (AHF) with ammonium hydrogen sulfate (AHS) and subsequently optimized. The optimized AHF/AHS etchant was evaluated on lithium disilicate glass, feldspathic porcelain, polymer-infiltrated ceramic network, and resin composite, and compared with hydrofluoric acid (HF), a commercial etchant (Monobond Etch & Prime; MEP), and alumina sandblasting. For lithium disilicate glass, shear bond strength (SBS) obtained with AHF/AHS treatment was higher than that with MEP but lower than that with HF. For feldspathic porcelain and polymer-infiltrated ceramic network, SBS obtained with AHF/AHS was comparable to those obtained with HF. For resin composite, SBS obtained with AHF/AHS was higher than that with untreated control while lower than that with sandblasting. Cytotoxicity evaluated using human gingival fibroblasts showed IC₅₀ values comparable to those of phosphoric acid and sodium fluoride.