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Dentistry/root canals and infections


QUESTION: When a root canal is done successfully, does the infection always go away or sometimes the infection lingers? When during a root canal, is the infection inside the tooth immediately gone and the infection on the bone takes time to heal? Can it take as long as weeks or maybe even months to heal? If after a root canal was done but infection or inflammation still in bone, does that mean the root canal has failed? What if after a root canal, we are not given antibiotics for weeks maybe months then we are put in antibiotics weeks or even months later, will the antibiotics work in getting the infection after the root canal was done weeks or months ago or do antibiotics have to be used immediately after the root canal? What's the time frame, if there is one. Thank you. Happy Memorial Day!

ANSWER: Hi Tatiana,

Happy memorial Day to you as well! And thanks to those who served our country....

Maybe the best way to answer your question is to explain how root canals work and what our goals are in treatment. When we do root canals, we use small instruments  and liquids to irrigate the inside of the tooth in an attempt to remove all the debris (dead pulp tissue) inside the root. It is nearly impossible to do this 100% since the root is curvy and has little side branches along it's length. Knowing this, the next goal is to create a seal at the end of the root so that any material that could not be removed would not be able to leach out the end of the tooth. In most cases, this is about 97% successful. However, that also means 3% of the time there are problems with remaining material causing a source for further infection. Healing is measured by lack of symptoms and reduction in the size of the dark spot on an x-ray. So, usually most of any infection inside the tooth is pretty gone or at least isolated immediately. However, for complete healing to occur in the bone, that can depend on how large the bone destruction was to begin with and can take a year or more to heal completely. During this time, however, there should be no symptoms. In our office we recall patients 6 months after treatment to evaluate healing....that's routine for ALL patients.

Right after a root canal is done, if there are symptoms, we may use antibiotics. If it's several months later, antibiotics might work if the patient is having symptoms to make them feel better until something more can be done as treatment. Antibiotics this late would not heal anything permanently.

All of what I have told you here is also variable depending on the patient's health and attitude. Everyone is different and treatment decisions are case by case. What I have given you are general guidelines.

Hope this helps and explains things.

Gary Backlund DMD, MSD

---------- FOLLOW-UP ----------

QUESTION: Hi Dr. Backlund, thanks for getting back to me. I think I do understand a little more about root canals. After retreatment of a root canal, how long should we expect the tooth to be sore for? What if it's sore for weeks upon weeks or maybe even months, does that mean the root canal has failed? The soreness is exactly the same as before retreatment. So after retreatement, if the tooth feels the same like let's say 2-3 weeks after root canal, does that mean it has failed? Any time frame on that? And as far as the antibiotics, you said after several months after treatment, it wouldn't heal anything permanently. What is the time frame for antibiotics to be taken after treatment in order for it to heal permanently? Hope that made sense. And can it be possible that the root canal failed simply because we didn't take antibiotics afterwards? Thank you.

Hi again Tatiana,

Let's deal with the antibiotics first. They will NOT heal an abscess. They will only help to heal the initial response of the body when the root canal causes the abscess to flare up. What heals the abscess long term is the root canal treatment itself. If antibiotics could heal an abscess, then there would be no need for root canals. Therefore, giving antibiotics months after a root canal will not make a difference except to relieve symptoms temporarily until the root canal can be redone, surgery performed or the tooth extracted.

We usually expect a tooth to be a bit sore for 3-4 days after treatment. If the symptoms last longer than that we might give antibiotics to help the body deal with the stirred up abscess at the end of the tooth. If symptoms persist for a long time, like your situation of several months, that would mean there is still a problem with the root canal that has not been solved by the treatment. Antibiotics will not heal the abscess this far after treatment.

I hope this clarifies things.

Gary Backlund DMD, MSD


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Gary Backlund, DMD, MSD


I am an Endodontist ( root canal specialist ) and can answer questions about root canals and their treatment. I cannot diagnose or treat online, but can answer general questions. I have been a specialist for 25 years and am Past President of the Washington State Association of Endodontists.


25 years practicing as a specialist

American Association of Endodonists, Past President Washington State Association of Endodontists.

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