Recent developments of new components for dental adhesives and composites

The currently used commercial self-etching enamel-dentin adhesives and restoratives composites are mainly based on a mixture of various monofunctional and cross-linking dimethacrylates. New developments of enamel-dentin adhesives concern the improvement of technique insensitivity and storage stability. Improvements of restorative composites are focused on the reduction of the polymerisation shrinkage, as well as the improvement of wear resistance, biocompatibility, and processing properties. In the past five years, many research efforts have been carried out to develop new monomers and tailor-made components for filling materials, such as fillers or initiators. New phosphonic acid ether acrylates and cross-linking bis(acrylamide)s enable the preparation of self-etching enamel-dentin adhesives with improved storage stability. With free-radically polymerisable cyclic monomers, such as bicyclic cyclopropyl acrylates or cyclic allyl sulfides, low-shrinkage storage-stable restorative composites could be prepared. In case of the cationic polymerisable cyclic monomers, like siloxane-based cycloaliphatic epoxides, the lower curing rate, stronger exothermic effect and lower curing depth compared to dimethacrylate-based composites presently prevent their dental application. Designed methacrylates with tailor-made properties and sol-gel polycondensates can also contribute to the improvement of the currently used restorative composites. Radical polymerisable dental materials are initiated by light curing and by redox initiator systems. Under acidic conditions amine containing initiator systems are deactivated by acid-base reaction. Non amine-based initiators have to be developed for acidic monomer containing dental materials. The use of discrete nano-filler particles mainly concerns the reinforcement and, in some cases, the increase of X-ray opacity of composite filling materials.