If you’ve ever had a dental filling, chances are you’ve got some mercury in your mouth. Those so-called silver fillings are a mixture of liquid elemental mercury and powdered silver, tin, copper, and other trace metals that hardens into a solid material that dentists have considered an excellent solution for cavities for more than a century. But concern has been growing as to the safety of these fillings, with some experts citing dental mercury’s dangers, especially to the kidneys and the nervous system.