What Needs to Be Done to a Root Canal Crown That Has Come Loose?

As soon as a crown becomes loose, saliva and bacteria have gotten in. Within 24 hours of exposure, decay begins (which is why we recommend brushing twice per day). The fact that is has come loose means there is a good chance there is decay present now.
More concerning though is the likelihood of root fracture. Normally in situations such as this, the root has fractured and there is no way to restore it. The tooth should come out. At that point you are looking at a bridge or an implant, and usually the implant is the better choice.
At a minimum, a new post and crown need to be made. A more likely scenario is that the tooth needs removal and an implant should be placed.

Most likely it’s not a big deal and the crown just needs to be recemented.  It’s usually a quick painless visit.  You should see your dentist to evaluate the tooth and recement it.  Don’t wait too long, because you risk losing or swallowing the crown.  Good Luck!

What you need to do is see a dentist. A few years ago, one of my patients had a loose crown and continued to postpone having it recemented. He swallowed it during dinner one night and a $100 recementation became a $1000 new crown. These things do happen, so get it checked as soon as possible.