At room temperature, mercury is a liquid into which some metals, ground into fine powder, can be dissolved. When silver is combined with a small amount of tin and copper and dissolved into mercury, the resulting alloy (called a dental amalgam) is strong at room- or even body temperature and easy for dentists to use to fill cavities in the back teeth. (The amalgam is too dark and too unattractive to be used up front.) The concern about dental amalgam is that over a person's lifetime, exceedingly small amounts of mercury are released into the mouth as vapor.