I would wait. I had a fever blister several years ago and once it's in your system it stays there forever. The herpes virus will remain in the trigeminal nerve forever. It can remain dormant for years but stress and sun can cause another outbreak. The trigeminal nerve goes to the mouth, nose and eye. Usually one sees a fever blister on the lips, sometimes under the nose. Ok, now back to my fever blister on my lip. Had it one time years ago and it went away, or remained dormant. I had extensive dental work done on my right upper side which triggered the herpes virus to become active, but instead of going to my lip, it went to my right eye, so I had a fever blister in my eye. That can be very serious and a leading cause of corneal transplants. I went to an eye dr and he prescribed antifungal eyedrops...it went away without causing scarring to my cornea. The chance of me getting ocular herpes again is 100%, could happen in one month or ten years. I always have to keep the eye drops available in case I get symptoms, then I have to start the drops within 6 hour of the first symptom. Since a root canal is stressfull and usually takes about 2 hours I wouldnt risk having an active case of herpes and having dental work done. Search ocular herpes.