After a facial accident when younger one of my upper front teeth turned dark grey so I went to a specialist and he did a root canal on the tooth (the nerve had died) and afterwards inserted a bleaching agent into the tooth and then sealed it. The tooth looked great if not a shade whiter than the tooth next to it plus I didn't need to get it crowned or do anything destructive it - even bonding requires that the tooth be prepped in some way. Check wit your dentist to find out what options are available and/or right for you.