History, state of the art and future demands of composites

But resin composite restoratives did never manage to fulfill all the demands of clinicians: First, only indicated for anterior teeth due to high abrasion plus room for improvement in aesthetic appearance in anterior teeth. Then, as micro-filled resin composites were introduced, clinicians were excited about the polish and aesthetics, but not of physical properties as flexural strength. Hybrid resin composites as the perfect combination of the advantages of micro- and macro filled resin composites became the golden standard. Nano technology was introduced to improve aesthetic appearance, polishability as well as handling properties. Nano-hybrids became the next step then after.

Over years and over generations of materials, main concern was shrinkage and shrinkage stress: Dentists asked for low shrinkage resin composites: They've got low shrinkage composites: Highly filled with a high modulus, resulting in comparable shrinkage stress as conventional hybrid resin composites. It took a while since it was obvious that not shrinkage, but shrinkage stress is the main issue to look at. As a consequence of that, shrinkage stress came in the focus of research. It was clear that a significant reduction in shrinkage stress can only be achieved by means of new chemical origins of the matrix. The Silorane technology was in the main focus of interest here. With those ring-opening monomers, shrinkage stress was able to become reduced significantly for the first time.

Unfortunately, when research focused mainly on reduction in shrinkage stress or on improvement in aesthetic appearance, the physical properties of resin composites were removed from the focus of interest. None of the new resin composites with reduced shrinkage or shrinkage stress demonstrated significantly improved physical properties compared to their direct predecessors from the same manufacturer. But with today's extended indications for resin composites as cusp replacements, the improvement of physical properties should be taken into consideration, too. Therefore: further research in resin composites should focus on continuously reducing shrinkage stress, improvement of their long term physical properties, maintaining their aesthetic appearance once given right after finishing and polishing as well as on improvements in handling properties – because only that material will be successful in the hands of a dentist, which one gets along very well.