If you take good care of your teeth, you keep your whole life. Teeth are the hardest parts of your body. Sharks have three rows of teeth, and grow new teeth every time they lose. Fluoride has been added to toothpaste in the 70s. The first toothbrush was invented in 1770. That same year, William Addis, England, also invented the first artificial teeth, made in china. In 1790, American John Greenwood invented dental drill. It was very big and heavy, and the dentist should turn the handle (like a hand drill to make holes in wood) to remove the damaged part of the tooth. The process was very slow and painful, and people went to the dentist when they can no longer endure their toothache!