# A Literature Review of Adhesive Systems in Density: Key Components and Their Clinical Applications
## 6 Resin Adhesive Systems
### Etch-and-Rinse Adhesive Strategy  
When it comes to adhesive agents, the dental practitioner has various options, each with its clinical considerations. Choosing an adhesive agent is a critical decision that will affect the procedure's long-term success. Therefore, knowing the classification of the contemporary adhesive agents will assist the general dental practitioner in making decisions [15]. In 2003, [PERSON] et al. [263] suggested two different strategies of adhesive systems according to the way they interact with the dental substrate, these being the ER technique and the SE technique. The ER technique necessitates etching followed by rinsing prior to their use, whereas the SE products are applied directly to the dental substrate without any prior treatment. This class includes all SE adhesive systems. Each of these classes can either be applied in three or two steps for conventional adhesives requiring pre-etching, or in two or one step for SE adhesives [3; 9]. Irrespective of the adhesive system used, the bonding process starts with acid treatment to remove or stabilize the smear layer [9]. Behind this layer, this acidic treatment affects the enamel and dental surfaces. This process makes micro-roughness favorable to the penetration and diffusion of resin monomers. An adherent interphase and an ideal seal between dental substrate and biomaterial restoration will be formed after photopolymerization [9; 15; 33]. Essentially, the primary consideration in dental adhesion lies in determining whether to replace demineralized HAp or entirely remove the resin [10; 14]. According to previous research, the key component of adhesion to dental tissue is mostly micro-mechanical [4] (Figure 15). However, additional chemical interactions may also contribute to bonding when the adhesive comprises functional monomers capable of connecting to the HAp [43; 264]. This chemical component, whose short-term effect may be masked by the tenacity of the micro-mechanical anchorage, could play a significant role in the adhesion potential of certain low-acid self-etching adhesives and in the durability of bonded joints [4]. This simple ranking makes it possible to classify all the varieties of products currently marketed into four categories: ER III, ER II, two-step SE (SE II), and SE I [9; 15; 265] (Figure 16). ER III was introduced in the early 1990s as a family of adhesive systems [266]. ER III materials were the first to allow the complete removal of the smear layer and are still considered the gold-standard for dentin bonding [33]. In this system, the three main components (etching agent, primer, and adhesive resin) are generally packaged in separate containers and applied sequentially [10]. This concept of total-etching of the ER III systems involves:  
* Application of a solution or gel, usually H\({}_{3}\)PO\({}_{4}\) (with a pH of 0.1 to 0.4), for a period of 15-30 s on the enamel and a maximum of 15 s on the dentin (a duration longer than 15 s will cause \"over-etching\") [33; 267]. Etching agents are mostly colored gels (thickened by means of silica microparticles) that regulate the application and ensure that all the gel is rinsed off the tooth substrate [15]. * Copious rinsing (15 s and more) using an air/water spray to remove the residues that result from the chemical reaction between the acid and the minerals. However, the surface must remain moist in order to prevent collagen collapse. This is done using a dry applicator, absorbent paper points, or air that removes any excess humidity [9; 10; 266]. * Once the dentin is moist, the application of a hydrophilic primer solution on enamel and dentin in several layers will be necessary to infiltrate the exposed collagen network, followed by a slight air pump for 5 s to eliminate the solvent (depending on the solvent). Thus, the dentin will exhibit a glossy appearance [9; 10]. * Application of adhesive resin on enamel and dentin, followed by the elimination of excess adhesive by a dry micro-brush. Afterwards, polymerization is done according to the manufacturer's recommendation.