What is filling made of? Is it safe if there for life?

Nothing toxic. Amalgam has been around for almost 200 years. The mercury bonds the other metals together and therefor is not "free" to get into your body in any significant amounts. The ada, the ama, and the fda have all done extensive studies to conclude that amalgam is safe. I have a couple in my mouth. That said, I don't place amalgam fillings in my practice because nobody likes the looks of them.
Metal fillings. Amalgam fillings are not safe. They contain 50% mercury which is a toxin mixed with silver, tin, copper. Eating or drinking hot fluids releases small amounts of mercury which are inhaled and absorbed. See utube "smoking tooth". If removed needs to be done safely to avoid more exposure. Have a urine heavy metal challenge test by genova, etc with a chelating med to measure stored levels in your body.