Dental adhesives are bonded to a wet surface of live tissue, dentin. There are two important stages of surface preparation for adhesive application: 1) Etching the tooth structure creating a layer of collagen network free from mineral, and 2) Applying a primer, in this case a water solution of hydrophilic monomer of 2-hydroxyethylmethacrylate (ScotchBond Multipurpose®, 3M). During the priming stage, the resin monomer should penetrate the fibril network and coat collagen fibrils. Subsequent adhesive resin penetration into the collagen network (hybrid layer) is not uniform, influenced by the presence of residual water and degree of resin polymerization. Dependence of bond strength of dental adhesives on time or intensity of light activation is well known, but no direct microscopic observations of the dynamics of polymerization were performed. This was due to the fact that during specimen dehydration for conventional SEM the polymerization process is still proceeding and residual monomer could be washed out.