An amalgam is a mixture of mercury with some other metal, used as a filling material in the general practice of dentistry. The amalgam, upon placement, can take up to two weeks to achieve it's final set strength, so, based upon that, I would tend to vote for the first two selections, either six to ten percent. Amalgam is resistant to the moist conditions found inside the human mouth, and has been used as a dental filling material for the past one hundred years. Amalgam had it's beginnings in France. It is still used today as a filling material because it is relatively inexpensive and easy to apply and shape. Concerns have recently arisen over the fear of exposure to mercury vapor upon the deterioration of the amalgam, or the removal of the amalgam. Composite materials are gaining ground on the amalgam, particularly because of the health concern and the increased desire to use materials which blend better with the teeth's natural appearance.