Every dentin adhesive system has specific application instructions. Following these instructions is always a critical factor in achieving the same bond strengths and performance that they produce in studies. One of the directions that is common to all of the self etching systems is to actively apply the self etching component. Different manufacturers use different terminology, for example, agitate or scrub. Regardless of the semantics, making sure to actively apply the product to the dentin surface for the length of time specified is critical.
This active application is responsible for removal of the smear layer and a chemical reaction of the monomer due to contact with the dentin. The side effect of not actively applying self etching adhesives will be many, and due to inadequate removal of the smear layer, inadequate hybrid zone development, and inadequate polymerization. These changes to the chemistry show up clinically as post operative sensitivity and premature failure of the restoration due to marginal breakdown, recurrent decay or debonding. If you need to confirm the directions for your dentin adhesive, most manufacturers post them on their company websites.