This report summarizes the two different adhesive systems, their components, the factors that influence adhesion and the state of the art of each system. The techniques of bonding the resin to the dentin: There are two techniques that have been used for the adhesion of the resin to the dentin: total etch and self-etch techniques. (1) Total etching technique: The total etching system was introduced by Bertolotti and Kanca after elaborating the research of Fusayama and others in Japan. This technique requires the use of phosphoric acid as an etchant for both dentin and enamel, and subsequently hydrophilic resins. According to studies, the technique is considered safe and does not have harmful effects on the pulp, as was once thought. Furthermore, numerous products that depend on the total etching technique are still available in the markets such as: OptibondFL and Perma Quick. The technique involves three steps (1-3), starting with the use of phosphoric acid which involves the removal of the smear layer, the opening of the dentinal tubules and the decalcification of the intertubular and peritubular dentin with consequent loss of inorganic matter. The second step involves the application of a primer that contains acetone, ethanol and/or water and one or more bifunctional resin monomers to wet the dentin, followed by the application of a bonding agent as a third step.(1)This system can can also be divided into 2 steps and this depends on whether the primer arrives separate or combined with the bonding in a single bottle. The simple 2-step version combines the priming and bonding steps together but with separate etching and rinsing steps. (2) To achieve a favorable dentin bond, several significant factors are needed, such as ensuring resin penetration into the dentin after inorga loss...... middle of paper...... f -etch adhesives . (5) Importance of maintaining hydroxyapatite at the interface After the application of self-etch adhesives, some dissolved hydroxyapatite crystals remain as a residue surrounding and protecting the collagen fibrils. A chemical interaction can also occur between these crystals and self-etch adhesives. (5) Self-etch enamel Selective etching of enamel margins with phosphoric acid, essentially transforming a two-step self-etch into a three-step adhesive, is highly recommended to combine a more favorable etch-and-rinse treatment on the enamel with a gentle self-etching. etching approach that appears to provide better long-term prospects for dentin. (5)Conclusion: Finally, it is important for the dentist to choose the most appropriate technique based on the details of the case and taking into consideration the problematic characteristics of the dentin due to its variances.