The Properties and Selection of Posterior Direct Restorations

Early tooth-colored restorative materials were weak and only suitable for anterior teeth. Over time, composites were developed that offered improved properties enabling their use in posterior teeth where subject to occlusal loading and forces of mastication. Secondary caries is the main reason for failure of both amalgam and composite restorations. Amalgam restorations offer ease-of-use but poor esthetics. In the case of composite restorations, minimizing polymerization shrinkage, wear and discoloration increase the longevity of these restorations. Posterior composite resins offer excellent esthetics, the main driver for patients who prefer composite fillings. Introduction Historically, posterior direct restorations involved the use of amalgam. The first modern tooth-colored restorations used acrylic, which was introduced more than six decades ago. Subsequently, silicates and (di)methacrylate materials were investigated. Silicate cements and early composite materials were suitable only for anterior restorations due to their weak physical properties, and the silicate cements needed to be placed in one movement – incremental placement was not an option. Silicate cements had a high failure rate. Old silicate restorations were assessed for longevity in a 1986 study and were found to have an estimated 66% replaced due to marginal discrepancies and lost fillings.1 Early resin-based composite restorations were an improvement over silicate cements; however, they were self-curing and required mixing of a base and a catalyst for curing, resulting in operator error during mixing and difficulties in timely and accurate placement. In addition, strength, bonding and retention were poor. Light-cured dimethacrylate composite restorations were introduced in the 1970s.2 By the 1980s, posterior tooth-colored restorations had been introduced, and these have continued to evolve to offer improved physical properties, user-friendliness and esthetics. Bonding systems and techniques have also evolved. Figure