The Progression of Dental Adhesives A Peer-Reviewed Publication Written by Ara Nazarian, DDS

There has been dramatic progression in the adhesion of dental adhesives and resins to enamel and dentin in the 40 years since Buonocore1 introduced the technique of etching enamel with phosphoric acid to improve adhesion to enamel. The first dental adhesives bonded resins to enamel only, with little or no dentin adhesion. Subsequent generations have dramatically improved bond strength to dentin and the sealing of dentin margins while retaining a strong bond to enamel. With more patients demanding metal-free dentistry, the use of dental resins as cements as well as direct and indirect restorations will continue to increase. This article discusses the progression of dental adhesives up to the most recent generation, in which all components are contained in a single bottle or unit-dose container and applied using a one-step technique that requires no mixing. Overview Over the past 45 years, dental bonding systems have evolved with variations in chemistry, application, mechanism, technique, and effectiveness. This evolution accompanied the development of improved esthetic dental materials, notably composite resin and ceramic, and an increasing demand by patients for esthetic dentistry. In 1999, approximately 86 million direct resin restorations were placed. With respect to indirect restorations, approximately 2.5 million veneers, 38 million resin/ceramic crowns, and 1.1 million ceramic/ porcelain inlays were placed, in addition to metal-based crowns and bridges and core/post and core build-ups.2 All direct resin restorations require bonding, and indirect restorations either require or are candidates for bonding. As the demand for bonded esthetic restorations has continued to increase, the evolution of bonding agents has accelerated. Let us quickly review dental adhesives according to a series of generations, allowing us to understand the characteristics of each group. All direct resin restorations require bonding History of Bonding Agents First and Second Generation The firstand second-generation bonding agents used during the 1960s and 1970s did not recommend etching the dentin, but instead relied on adhesion to the attached smear layer.3 The weak bond strength (2MPa–6MPa) to the smear layer still allowed dentin leakage with clinical margin stain.4