A composite filling is a tooth-colored plastic and glass mixture used to restore decayed teeth. Composites are also used for cosmetic improvements of the smile by changing the color of the teeth or reshaping disfigured teeth.
Aesthetics are the main advantage of composites, since we can blend shades to create a color nearly identical to that of the actual tooth. Composites bond to the tooth to support the remaining tooth structure, which helps to prevent breakage and insulate the tooth from excessive temperature changes.
Most people recognize dental amalgams as silver fillings. Dental amalgam is a mixture of mercury, silver, tin and copper. Mercury, which makes up about 50 percent of the compound, is used to bind the metals together and to provide a strong, hard, durable filling. After years of research, mercury has been found to be the only element that will bind these metals together in such a way that can be easily manipulated into a tooth cavity.
Mercury in dental amalgam is not poisonous. As mercury is combined with other materials in dental amalgam, its chemical nature changes, so it is essentially harmless. The amount of mercury released in the mouth under the pressure of chewing and grinding is extremely small and no cause for alarm. In fact, it is less than what patients are exposed to in food, air and water.
Ongoing scientific studies conducted over the past 100 years continue to prove that amalgam is not harmful. Claims of diseases caused by mercury in amalgam are anecdotal, as are claims of miraculous cures achieved by removing amalgam. These claims have not been proven scientifically. (Source www.knowyourteeth.com )