I have so much metal in my mouth that it’s a surprise I make it through airport metal detectors. My lot began way back when I was a teenager. I wasn’t a good boy and didn’t brush and floss like I should have. As a result I wound up with a whole bunch of steel fillings in my back teeth.
The dentist said I had lost so much of my teeth to cavities that I came close to having a root canal. After I had those steel fillings I had to take pain killers because of the intense pain for several weeks.
Later in life I had those fillings leveled off and got gold crowns. I also have one porcelain crown. That should do it for awhile. They can make fillings out of everything I suppose, but the mercury fillings are the cheapest. It just depends on personal preference and aesthetics.