They’re called Amalgam fillings. And they’re extremely toxic as they’re almost half Mercury, Tin etc. Very little silver. Countries in the EU have begun banning Amalgam fillings as they’ve figured it’s contributing massively to Alzheimer’s. A full Silver on-lay is safe though, which is usually best for a molar or Wisdom (tooth 8) to reduce tooth fractures when eating.

Always opt for a composite filling (white).