How safe are cobalt-chromium and nickel-chromium alloys used in dental implants (porcelain fused metal)? IARC groups nickel and cobalt metals in group 2B and chromium in group 3 (hexavalent chromium is group 1!). But what is the likelihood of these metals leaching from implants and affecting the body? Aren't some of these metals already used for kitchenware (stainless steel vessels for instance contain chromium) and in industrial containers used for food processing? Is the risk much higher when these metals (not their more toxic compounds/salts though) are present in mouth when compared to their being used for food storage or cooking?
Alloys have completely different chemical properties than their component elements. Elemental mercury is liquid, and is toxic, but when alloyed into amalgam with silver, tin, and some other elements it is perfectly safe, and has been used in dental fillings for a very long time with no negative effects. The same is true of cobalt and chromium alloys - they are chemically bonded to the other elements in the alloy, making a new molecule, and cannot "leach out" without the chemical bonds being broken, which cannot happen in the mouth or at standard cooking temperatures. Hence, they are safe for food prep and for fillings/implants.