Retreatment of root canal treatment, can I retain my previous crown?

If your porcelain crown had a great fit but it did come out, you can definitely have the root canal redone due to an infection and your dentist can reverse fit your crown back! It is a bit technical but it can be done if your Endodontist makes a conservative access hole to retreat your infected root canal.
The most important question is : if your crown was retentive enough, is the margin ( The Fit) of your crown satisfactory to begin with, if not definitely you will be needing a new porcelain crown.

There is a small chance that your crown will fit after your root canal is redone.  Your dentist will need to make sure the margins are sealed, the crown is in excellent condition, and that there is no decay that was underneath the crown.In most cases, however, the crown you had probably will not fit after your root canal is retreated.  If this is the case, for an ideal fit, it would be wise to get a new crown that fits well to avoid future problems!

Hi:
As long as the margin of the crowns are sealed you can reuse the same crown without any problem.
Best,
Dr. Maddahi

Yes, you can use previous crown but it should be in good condition, has closed margins, and there is no decay underneath the old crown. 
However, if the old crown has cavities or poor margins, then a new crown will be needed. So, firstly you need a clinical exam and x-ray to check the crown.
Good Luck!!