I can't speak for your situation, but there was more than mercury vapor under my crown. I chose to have it removed to go for a metal-free mouth. When it was removed, there was a very large mercury filling underneath, still all shiny and pretty since it had been hidden from the elements by the crown. According to my dentist, there is really no good way to tell what is underneath until the crown is removed. He said sometimes there is nothing; other times are like mine. Definitely keep doing your own research, though. I just wanted to share my experience and let you know that you may have more than vapor (or you may not)!