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 (Dunn, 2003). 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. 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.
One of the primary goals of root canal treatment is to eliminate bacteria from the root canal system to the greatest possible extent . Bacteria have been shown to be the etiology for apical periodontitis and to be the cause of endodontic failure. One of the goals in restoring of the tooth after root canal treatment should be to prevent recontamination of the root canal system. Gross contamination can occur during the restorative process from poor isolation or poor aseptic technique. Contamination can also occur from loss of a temporary restoration or if leakage occurs. The same things can occur with a “permanent” restoration, but “permanent” materials tend to leak less than temporary materials. Exposure of gutta-percha to saliva in the pulp chamber results in migration of bacteria to the apex in a matter of days. Endotoxin reaches the apex even faster.
First and Second Generation
The first- and 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. The weak bond strength (2MPa-6MPa) to the smear layer still allowed dentin leakage with clinical margin stain (Pedigao et al. 2001).
The third-generation systems of the 1980s introduced acid etching of dentin and a separate primer designed to penetrate the dentin tubules as a method to increase bond strength.3 These systems increased bond strength to dentin (12MPa-15MPa) and decreased dentin margin failure. With time, however, margin staining caused clinical failure (Miller, 2002).
The fourth-generation adhesive systems of the early 1990s used chemistry that penetrated both etched and decalcified dentin tubules and dentin substrate, forming a “hybrid” layer of collagen and resin. Fusayama5 and Nakabayashi6 described the penetration of resin into dentin as giving high bond strengths and a dentin seal. In fact, Kanca introduced the idea of “wet bonding” with these systems. Products in this category include All-Bond® 2 (Bisco), OptiBond® FL (Kerr), and Adper™ Scotchbond™ Multipurpose (3M ESPE). These bonding agent systems have the longest track record as far as research goes and they perform well clinically.
In fact, OptiBond FL, an 18-year-old product, received the Product of the Year award ...