Re: Crown and core fell out can old crown be re-used?
I don't believe a crown with core can be reused. The post would be permanently cemented onto it and they would not be able to be separated. A whole new post and crown would have to be made.
An implant probably wouldn't run much more than a new post and crown, esp if the tooth doesn't have much to work with already. You may want to check with your dentist on the feasibility of long term survival for the tooth in question. With a core that has had 6 crowns already, it may not be able to hold another at all and restoration is questionable.
GOOD LUCK. IMO, the best long term result for a crown in your case would be an implant.
My best to you,