Can you cover existing metal crowns with porcelain or another product to make them white?

Hello there,I would not recommend placing any type of material or veneer over your metal crowns.  If you're unhappy with your crowns, I would suggest seeing a cosmetic dentist who can replace your current crowns with all porcelain crowns. Always look at before and after photos when selecting your dentist. This will give you a pretty good indication of what you can expect. Good luck and I hope this helps. Follow me if you have more questions.Sarah Thompson, DMDSt. Louis, MO area (O'Fallon, IL)Real Self 100

Covering existing metal crowns in the mouth is not possible. Achieving a strong bond to the metal would not be easy. 

Trying
to cover existing crowns in the mouth doesn’t work very well. Porcelain fused
to metal crowns have the porcelain baked on at high temperature in an oven,
something that obviously can’t be duplicated in the mouth. It’s better long
term and probably less expensive to just cut off the old metal crowns and
replace them.