How does a tooth stay alive in your mouth and survive after a root canal if there is no root left?

Only the nerve: Only the nerve tissue inside the root is removed. The root is left in place. For more info on root canals check out this webpage...http://www.laserdentistbaltimore.com/laser-assisted-root-canals-with-pips/

Root is still there: Only internal nerve and blood vessel has been removed (they reside inside the root known as the canal).

Non-vital: The tooth is said to be non-vital, not "dead". The nerve and blood supply to the tooth is removed from inside the root and crown of the tooth. The actual root is not removed. A common misconception by non-professionals. The root is still attached and gets nourishment from a membrane between the bone and root. Think of it being similar to your hair where you can cut it but still attached to scalp