# A Literature Review of Adhesive Systems in Density: Key Components and Their Clinical Applications
## 6 Resin Adhesive Systems
### Universal Adhesives
Scotchbond Universal Dual Cure Activator (Scotchbond Universal, 3M ESPE, St. Paul, MN, USA), One Coat 7 Activator (One Coat 7 Universal, Coltene, Altsattaten, Switzerland), and Clearfil DC Activator (Clearfil Universal Bond Quick, Kuraray Noritake Dental Inc., Okayama, Japan) are examples of the aforementioned activator. However, some UAs like All-Bond Universal (Bisco, Inc., Schaumburg, IL, USA) do not use a separately applied activator, due to their compatibility with self-curing materials. Indeed,  
Figure 19: Classification of dental adhesive systems according to their protocol of clinical application (etch-and-rinse, self-etch, or “universal”; and one, two, or three steps) [289]. this adhesive (All-Bond Universal with a pH = 3.2) is less acidic (not usable as SE on dentin) than other UAs (2.0 < pH < 3.0) [298]. UAs are not to be confused with SE I single-bottle or \"all-in-one\" systems. These adhesives have distinct chemical compositions characterized by the presence of carboxylate or P monomers. The most used monomer is 10-MDP. Nevertheless, UAs contain a variety of additional functional monomers, including GPDM, PENTA, 4-MET, and 4-META [15]. The acidic monomer 10-MDP, which had been utilized by one SE adhesive system (CSE (Kuraray Noritake Dental, Tokyo, Japan)) for years, was incorporated to UAs once the patent expired [34]. The pioneering product of this category, Scotchbond Universal by 3M ESPE in St. Paul, MN, USA, featured 10-MDP [299]. This was followed by numerous adhesive systems made by different manufacturers. This 10-MDP monomer proved to generate a stronger and more stable bond with the tooth structure than the acidic monomers previously employed [34]. These UAs facilitate both micro-mechanical retention and chemical bonding with the dental substrates [172; 15]. 10-MDP has a high affinity for HAP and forms chemical bonds with apatite crystallites via ionic bonding. The concentration of 10-MDP differs across UAs. It has been demonstrated that the higher the monomer concentration, the higher the adhesive's BS [15]. UAs strengthen adhesion to ceramic restorations. Indeed, UAs with 10-MDP improve adhesion to zirconia [300; 301; 302; 303] and indirect resin-based composites [304]. On the other hand, UAs have proven incapable of replacing silane-based primers for glass ceramics such as lithium disilicate ceramics [305; 306; 307]. This class of adhesive systems should also include water in their formulation to dissociate acidic monomers and to make the SE procedure possible [287]. One of the many dilemmas confronted by chemists in evolving UAs is that water can degrade the chemistry of these systems, contribute to monomer separation, reduce shelf-life, and thus pose a challenge during evaporation [287; 308]. In a previous study, [PERSON] et al. [308] stated that UAs with 10-15% of water (Scotchbond Universal (3M ESPE, St. Paul, MN, USA) and Prime & Bond active (Dentsply DeTrey GmbH, Konstanz, Germany)) are optimal for lowering the impact of surface wetness, while adhesives with more than 25% (G-Premio Bond (GC Corporation, Tokyo, Japan) approximately 25%) of water content and adhesives with water content < 3 vol% (All Bond Universal (Bisco, Inc., Schaumburg, IL, USA)) experience phase separation. In the air-drying step, residual water may cause inadequate polymerization of the adhesive, increase hydrolysis after polymerization, and generally degrade the adhesive surface [23]. The addition of ethanol or acetone to UAs formulations increases resin wetting, infiltration of dental tissues, water elimination, and evaporation during the drying process [309]. Some UAs also state that they can be used instead of silane coupling as agents for bonding to silica-based ceramics (feldspath, lithium disilicate, etc.) [309]. Nonetheless, indirect restorations showed stronger bonding efficacy when silane and bonding resin were applied independently, resulting in a superior BS to an etched glass-based ceramic substrate after one year of water storage [304]. Several silanes are extensively utilized in the industry.