Acidic

Acid etchant is available in the form of a solution or gel of phosphoric acid and is usually available in concentrations of 15%, 34% or 37% (37% is the most common concentration available on the market). The acid etchant creates microscopic spaces in the enamel (increasing surface roughness) through which the bonding agent or adhesive flows and aids in the bonding process (micromechanical retention).