Composite Resin Fillings Silver fillings have been used for decades, and eventually these fillings need to be replaced. Composite resin fillings are made from a natural looking synthetic material. Besides standing out as dark patches against your white teeth, old-fashioned “amalgam” fillings are made from metals which oxidize and corrode over time through normal wear and tear. This wear can cause gaps that let bacteria into your tooth, or expansion which can cause cracks and fractures in your teeth. Composite resin replaces “amalgam” fillings and can last many years with proper care.