# A Literature Review of Adhesive Systems in Density: Key Components and Their Clinical Applications
## 6 Resin Adhesive Systems
### Self-Etch Adhesive Strategy
In order to overcome this problem, etching the enamel first with traditional H\({}_{3}\)PO\({}_{4}\) at a pH of less than 1.5 is preferred [45; 280]. However, some of these products are slightly acidic, with a pH as high as 3.3 [9]. In addition, practitioners using this technique should be careful to confine H\({}_{3}\)PO\({}_{4}\) only to enamel. Further etching of the dentin with H\({}_{3}\)PO\({}_{4}\) could create a conflict, \"over-etching\", where the demineralization zone is too deep for the subsequently placed primers to penetrate completely into the demineralized dentin [9; 278]. These systems are popular because they are easy to use, with a lower postoperative sensitivity. The reason that self-etching systems tend to minimize postoperative sensitivity is that the smear plugs in the dentinal tubule are left intact [33]. The benefit of SE II adhesives is that their effectiveness is less reliant on the level of dentin's moisture comparing to ER adhesives. Normally, SE II adhesives were described to have better bond stability when compared to SE I adhesives [15; 33]. Further, SE II systems are classified into two types:  
* Type I adhesives, which are self-etching primer and adhesive systems such as CSE (Kuraray Noritake Dental, Tokyo, Japan), Prelude SE (Danville Materials, San Ramon, CA, USA), and Ultradent Peak SE (Ultradent Products Inc, South Jordan, UT, USA). These adhesives have liquid components including a self-etching primer and an adhesive resin, which are applied separately to the tooth and are generally compatible with self-cured composites. * Type II adhesive systems such as All-Bond SE (Bisco, Inc., Schaumburg, IL, USA), Brushk&Bond (Parkell, Edgewood, NY, USA), Futurabond NR (VOCO America, Inc., Cuspis, CA, USA), Touch&Bond (Parkell, Edgewood, NY, USA), Adper Prompt L Pop (3M ESPE, St. Paul, MN, USA), and Xeno III (DENTSPLY Caulk, Milford, DE, USA). Figure 17: Selective enamel etching. (Courtesy of Prof [PERSON]). They use a self-etching primer and adhesive that are mixed together prior to placement and are not compatible with self-cured composites [9; 15; 33]. Note that the enamel and dentin BS of SE II is lower compared to the ER III and ER II [9]. However, this might be controversial for other researchers [33; 266]. SE I (all-in-one) adhesives were introduced in the late 1999 and early 2005 [9; 266]. They contain a formulation that mixes a self-etching primer and an adhesive resin in a single bottle [49; 278]. SE I systems are theoretically capable of etching and infiltrating both enamel and dentin. The self-etching primer creates a resin layer that bonds with the composite material through photopolymerization [15]. Clinically, this system is the easiest to use, and BS values are generally acceptable [9; 262]. Despite the simplicity of the bonding operation, it was possible to eliminate the errors that could occur while mixing several separate components [33]. However, placing and incorporating all the chemistry required for an adhesive system into a single bottle, and keeping it stable for a reasonable period of time, is a significant challenge [9]. These acidic systems contain a significant amount of hydrophilic monomer in their formulations contributing to the increased permeability of the HL and may be subjected to hydrolysis and chemical decomposition [281]. In addition, once the SE I systems are placed and polymerized, they are mostly more hydrophilic than SE II systems; this condition forms water-filled channels that limit the depth of infiltration of the resin into the dental surface and leads to water infiltration from the dentin through the HL. This phenomenon creates voids with a poor sealing ability (Figure 18). The hydrophobic monomers contribute to more stable polymers [23]. SE I adhesives have proven to have the lowest initial and long-term BS of all the adhesives on the market. However, this can be considered a disadvantage [282]. In addition, they presented an incompatibility with self-curing resins and a reduction in shelf-life [15].