The Organic Matrix of Restorative Composites and Adhesives

The evolution of dental composites has been astounding since they were first introduced in the early 1960’s. The concerns involving wear of posterior restorations have been virtually eliminated with the introduction of novel filler technologies, which have expanded the realm of applications of these materials. The organic matrix of the material, however, has remained largely unchanged since the early days, and still relies on methacrylate chemistry in virtually all materials currently commercially available. Methacrylates are undoubtedly well-suited for this application, due to the relatively fast polymerization rates at room temperature, and the possibility for on-demand cure via photo-activated mechanisms. Many different photoinitiators have been proposed, and more recently, alternative visible light initiators that are white in color have been used to produce even more esthetic shades. The major potential drawback involving methacrylates is the presence of the relatively labile ester bond, which may be degraded in the presence of aqueous solutions and/or by the action of salivary and dentin-derived enzymes. This degradation of the organic matrix is one the factors responsible for the relatively short life-time of these restorations, with several reports in the literature pointing to an average of 10 years or less. For that reason, in the last 10 years or so, a lot of effort has been concentrated in innovation of the organic matrix phase, with emphasis in alternative chemistries. This chapter will focus on the recent developments in monomers and additives proposed to enhance the durability of dental composite restorations, including materials with reduced degradation and polymerization stress and increased resistance to fracture. Ultimately, the authors seek to stimulate a reflection on the future perspectives for materials development for this application.