I have a crown on #18. It is a live tooth. X-rays do not show any decay. Is there any way to remove and reuse the crown?

They do look pretty wide.  Not much you can do other than replace them.  From the photos the case would turn out much nicer if you did four teeth as opposed to two.  Best of luck.  

The sensitivity to heat is suspicious.  You should get back with endodontist who did root canal and have him(her) do tests to determine if in fact it is this same tooth causing your pain or could it be another tooth reacting to this heat..

Teeth can be sensitive for a time after work performed even if everything is performed properly..That said, if tooth is not getting better after reasonable time you should go back to have bite checked again and or determine cause of your pain ie..nerve involvement, loose temporary, gum...