Q.
Hi
About 5 years ago I had 2 crowns fitted to my 2 front teeth.
I went to the dentist yesterday as I have noticed in the last year or so that one of the crowns has developed a grey line at the top at the gum line.

I seem to recall being told before that this was often an issue with crowns as the gum recedes. However when I asked my dentist about the cause, she said that it was nothing to do with gum recession but that she thought there was a problem with the crown. She thinks it might have a crack in it which is causing bacteria to get in and rot the remaining bit of tooth underneath and hence making it go black. She suggests replacing both crowns to ensure a colour match.

Could you give me your opinion please as to the likely cause of this dark line?
Her advice would be very expensive and disappointing after only having them done 5 years ago.

Thanks