What if I have crowns on my front teeth and I want to bleach?

I have porcelain fused to metal crowns on my two front teeth. I have had them for a few years now and the black line at the gum line is starting to show, and the crowns appear to be alot bigger than all my other teeth. I have decided to replace these crowns will all porcelain crowns, however I want my teeth whitened as well. Would I have to get my real teeth whitened before replacing the crowns with all porcelain so that the dentist can choose the colour to go with my new whitened teeth?
– Sophie from England

Sophie,
That’s smart to be replacing your existing porcelain fused to metal crowns with all porcelain crowns, since they’re on your very front teeth. That dark line at the gumline can really spoil the looks of those teeth, and they will look opaque. But be sure to go to a dentist with lots of experience in cosmetic dentistry. There are special techniques in doing them, and you don’t want to be your dentist’s guinea pig for this type of crown. Very few dentists will let on to the patient if they’re uncomfortable or unfamiliar with a procedure.

When we do any work in the front, like say two new crowns, as you’re having done, we encourage patients, if they have any idea that they would like whiter teeth, to go ahead and bleach them first. But then you can’t do the crowns immediately after being done with the bleaching, because in the first two weeks after bleaching, there is a slight color relapse. What happens during the bleaching is that peroxide filters into the tooth and releases little oxygen bubbles inside your teeth. This is what oxidizes away the stain and dark colors. But while those tiny oxygen bubbles are present, your teeth will look artificially whiter. You need to give them about two weeks for the whiter color to stabilize, and then you match that color with the new crowns.