Bonding of zirconia crowns and bridges to abutments is important, not only bonding of the thin resin layer to the abutment, but also bonding to the zirconia ceramic is crucial. Both mechanical and chemical adhesion are desired. Mechanical retention of dental porcelain achieved by etching with moderately concentrated hydrofluoric acid is not possible with zirconia ceramics. The purpose of this study was to show that etching is possible with relative low melting fluoride compounds such as ammonium hydrogen difluoride and potassium hydrogen difluoride.