Summary For a four-component acrylate adhesive system the influence of viscosity and penetration on adhesion to enamel was investigated. While low viscous monomer adhesives yield both inter- and intraprismatic penetration in enamel after polymerization, highly viscous adhesives result in the former type only. This difference in penetration of the adhesive in enamel is reflected quantitatively in the tensile strength values. Scanning electron microscopic measurements on the tag formation under various circumstances have been carried out. The SEM experiments show, e.g. that at polymerization times less than 1·5–2 min (a clinical necessity) polymer-tags were usually fractured from the bulk material due to stresses generated.
