Just had Lumineers put on 2 weeks ago and they are turning grey, especially closeto the gum line. yesterday one fell off and the cement underneath was black! the black came off easily with peroxide...but what about my other teeth? howcan i get the stain out from under them? the dentist didn't know why this is happening. he told me to bleach them and the stain should come out, so far it hasn't...will this work?