Universal adhesives - a new direction in the development of adhesive systems

Abstract

Objectives: In the past decade, many new adhesive systems labeled as universal were introduced. Their common characteristic is that they can be applied to hard dental tissues either in self-etch or etch-and-rinse mode, and they are also able to bond to various restorative materials. Moreover, universal adhesives are mostly one-step and user-friendly. Because numerous papers about their properties were published, the purpose of this review article is to critically discuss the available information about the properties of universal adhesives and their bonding to various materials. Conclusions: The simplification of the application procedure is accompanied by several drawbacks associated with the necessity to mix all components into a single bottle. Due to the content of hydrophilic monomers, water and volatile solvents, adhesive layers of universal adhesives are more susceptible to water sorption. Consequently, they are more prone to hydrolytic and enzymatic degradation, thus exhibiting a lower durability. Universal adhesives also have limitations in bonding to some materials and require preceding surface treatments. To enhance the bond strength to enamel, selective enamel etching with phosphoric acid is recommended because the self-etching effect of universal adhesives may be insufficient. In contrast, more durable bonding to dentin was reported in self-etch mode compared to etch-and-rinse. For glass ceramics, a silane coupling agent should be applied in a separate step prior to the application of universal adhesives despite that some of them are silane-containing. The silanes are unstable in acidic conditions and their premature hydrolysis precludes the chemical interaction with glass. Lastly, zirconia ceramics require mechanical pre-treatment using air-abrasion because the chemical bond alone is not sufficient. In conclusion, universal adhesives can be used in various indications, however, it is necessary to be aware of their drawbacks and limitations.

Keywords

• adhesion
• universal adhesives
• enamel
• dentin
• ceramics
• resin composite
• review