Composite resin and amalgam dental filling materials

Dental caries is a major public health problem in most industrialized countries, affecting 60-90% of school children and the majority of adults. For the last 150 years, the most widely used material for posterior load-bearing restorations has been silver amalgam. Despite its long history in dental practice, the safety of dental amalgams has been questioned since their introduction to the dental practice. Most dental amalgams contain approximately 50% elemental mercury, a known toxic substance, which holds together the metallic constituents of the filling material. The initial safety concern was the risk of exposure to mercury vapor from the dental filling before its complete setting, and the filling was thought to be inert once it is hardened. However, some reports have suggested that stress on the amalgam surface, such as the normal masticatory function, may free mercuric vapor which can then be continuously introduced into the body. Tooth-colored resin composite materials are being increasingly used instead of silver amalgam, most probably due to their higher esthetic value and the increasing concerns about amalgam safety. However, some factors prevent the full adoption of composite materials as an alternative for amalgams. First, the clinical longevity of amalgam fillings is thought to be superior to that of composites; although a recent evidence-based review failed to draw any conclusions about filling longevity due to various limitations in the included studies. Second, the use and handling proprieties of composite are operator sensitive, and in the absence of ideal conditions and equipment, may result in more secondary caries around restored teeth and the need for more frequent replacement and repair of restorations.5 The increased cariogenicity of composite materials, in contrast to amalgam, can also be explained by the lack of antibacterial properties and their association with a favorable environment for cariogenic and pathogenic bacterial growth. In order to support the choice between dental amalgam or