New trends in dentin/enamel adhesion

The acid-etch-technique has provided an ideal surface for bonding to enamel by using 30-40% phosphoric acid. The resulting etch pattern is characterized by the profuse formation of microporosities which allow the penetration of monomers into those porosities to form resin tags that provide micromechanical retention. Successful attempts of bonding to dentin in a similar fashion have been reported more recently. Due to the specific properties of dentin, such as its tubular structure and its intrinsic wetness, bonding to dentin has not yet reached the ideal characteristics. In spite of the existing deficiencies in dentin adhesion, the increasing demand for esthetic restorations has generated intensive research on new esthetic materials with special focus on amalgam alternatives. The bonding mechanism of recent dentin bonding agents is based on the penetration of ambiphilic molecules into acid-etched dentin to form a lacework of dentin collagen and polymerized monomers. Dentin adhesive systems that contain a multitude of different bottles of different colors and shapes belong to the past. Because clinicians are increasingly eager to try new materials, the actual tendency calls for simplification of the bonding procedure e.g. one-bottle adhesive systems and all-in-one no-bottle materials. In spite of simpler materials, a separate etching step is still needed for one-bottle systems. Nevertheless, manufacturers of these simplified one-bottle materials recommend their use to bond polyacid-modified composites (compomers) without a separate etching step. The most recent addition to the group of simplified adhesives is the all-in-one no-bottle adhesives; one of these all-in-one systems, Prompt L-Pop (ESPE) has resulted in very promising laboratory results when used on enamel. In spite of the uncertainty about the capacity of all-in-one adhesives to etch enamel adequately in vivo, scanning electron microscopy studies have resulted in an enamel-etching pattern morphologically similar to that corresponding to phosphoric acid-etched enamel. While all-in-one adhesive systems have been reported to result in very satisfactory dentin bond strengths, results from other laboratories suggest that bonding to dentin with all-in-one adhesive systems will need to be somewhat improved. Clinical studies, which are the ultimate test for the acceptance of dentin adhesives, are now underway in several centers. Six-month data showed a very good clinical performance for this ultra-simplified all-in-one adhesive system.