It is generally accepted that the application of dentin-enamel adhesive should involve not only the etched enamel but also the dentinal surface. For this purpose, new bonding agents reqiring dentin etching and the combined use of bifunctional groups (Primers) as well as hydrophilic resins have been introduced. This study used scanning electron microscopy to analyze the relationship between dentil and fluid resin of three bonding agents. The results demonstrated that the adhesive monomers easily penetrated the etched dentin, sealing the dentinal tubules and creating a resin dentin interdiffusion zone (hybrid layer). As a result, the microleakage between dentin and resin composite restorations, responsible for postoperative tooth sensitivity, pulpal inflammatory reactopm. amd secpmdaru decau. os great;u rediced.