That is right, there is no “good or safe level” for mercury use. ... But American Dental Association (ADA) are very careful not to ever call it amalgam silver fillings and mercury fillings, even though 50% of an amalgam filling is composed of poisonous mercury. Intended to replace tooth structure lost to decay. Dental fillings may last many years; however, even- tually all fillings need to be replaced. Constant assault from eating and drinking, or stress from clenching or grinding, eventually may cause a dental filling to fail. Bacteria cause tooth decay Composite fillings are a plastic material that is customizable to match your teeth. Because composite materials contain absolutely no mercury, some experts feel it is a safer option than the old black amalgam fillings of the past. ... Some patients complain of hot and cold sensitivity with amalgam fillings, as well..