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Signs Of Infection After Root Canal

Updated: Apr 19, 2023

Root canals are used to eliminate nerve infections but teeth don't become immune to future infections just because they've been root canal treated. Yes, your root canal can get reinfected shortly after or sometimes many years later.

pimple on gums
pimple on gums

This article will describe all of the possible signs that may indicated an infection in root canal treated teeth. Some of them are obvious because they're painful while others are not since they're asymptomatic.

Signs of infection after a root canal:

Last but not least, we'll talk about what you should do about the infection and what could've potentially caused it.

Gum boil - pimple on the gums

A gum boil is a pimple on the gums that forms as a result of a tooth abscess. A tooth that has already been treated with a root canal should be devoid of any dental abscesses and infections. If you notice a pimple on the gums besides the tooth which had the root canal done, it means that the infection has returned.

gum boil
gum boil

What it looks like:

  • Small pimple located on the gums

  • Red to white gum boil

  • Pus may ooze out of it

  • May or may not be painful

This is a tell tale sign of an infection after a root canal. This tooth will require further treatment, most likely an endodontic retreatment.

Gum swelling

Gum swelling is not a good sign in general and if it happens around a tooth with a root canal, it isn't pure coincidence. There is something going on with that tooth and it is most likely a recurrent infection.

What it looks like:

  • Very swollen gums that look inflamed

  • Bleeds easily upon touching

  • Pus may or may not be present

  • Very painful to the touch

Fractured tooth

You may be surprised but teeth that have been root canaled but never received a crown are more prone to fractures. If you happen to bite down on something hard the wrong way, the entire tooth could crack in half.

fractured tooth after a root canal
fractured tooth after a root canal

Once the tooth is fractured, it is either infected or will become infected shortly afterwards. It is very important to get it treated immediately if you notice a fracture because the problem won't go away on its own.

What it looks like:

  • A crack in the tooth

  • The cracks may be from front to back or from side to side

  • It doesn't have to crack all the way through either

There is no home remedy that can cure a fractured tooth. In fact, your dentist can't even save it either because the only treatment left for this is to have the entire tooth removed.

Presence of pus

A tell tale sign of an infection is the presence of pus, which is a white fluid. The color is distinctly different from blood which is red. Purulence contains a lot of dead white blood cells and bacteria. The only reason why there would be white blood cells is because they were fighting an infection.

Signs and symptoms:

  • White fluid

  • May ooze out of a pimple or the gums

  • May or may not be painful

  • Foul taste in mouth

A fully healed root canal tooth should not have any pus oozing out of it whatsoever. Healthy teeth don't have bacteria and white blood cells actively fighting each other.

Pain upon biting

You may have finished the root canal and even put a crown on the tooth but for some reason when you're chewing with it, it hurts. Usually a tooth that has finished endodontic treatment shouldn't have anymore sensations because there is no nerve left in it.

If you're feeling pain when you chew, it could mean that a fracture may be starting or there is an infection that is brewing. You will need to see a dentist if you're experiencing this symptom. They may need to take a cone beam CT x-ray in order to see what is going on with the tooth.

You won't be able to tell what this condition looks like because the appearance of the tooth will look normal. In fact you won't really notice anything wrong with it aside from the fact that it hurts whenever you eat on it.

Periapical radiolucency on x-ray

The root canal tooth may look completely fine appearance wise and sensation wise. It doesn't hurt and it doesn't bother you. However, if your dentist takes an x-ray and sees a radiolucency at the tip of the root, it may indicate that there is an infection with the root canal.

radiolucency after root canal on x-ray

What it looks like:

  • Tooth appears normal in the mouth

  • On the x-ray it will have a big black circle around the tip of the root

Just a word of caution and that is if you recently had the root canal treatment done, the radiolucency at the tip could just need more time to heal. You have to take another x-ray in 6-12 months to see if the size of the radiolucency has changed.

  • Smaller radiolucency - the tooth is healing and you simply need to give it more time.

  • Larger radiolucency - the infection has returned and will need retreatment.

Severe pain

Even if there is no crack and no sign of pus, if you're experiencing severe pain from the tooth with the root canal, it is definitely an infection. Whatever it is, you will need to return to your dentist so that they can figure out what it is.

It will most likely need some sort of treatment such as redoing the root canal or maybe even a tooth extraction. You won't know until you get the diagnosis.

Fever and lethargy

After finishing the root canal, if you come down with a fever or you're feeling very tired it could mean that there is an infection. It may be related to the tooth or maybe it is coincidental.

Nonetheless, feeling unhealthy is not a good sign and will need to get checked out. If your dentist can't find anything wrong, you may need to go see your primary care doctor.

What to do about an infection after a root canal

You will definitely need to return to your dentist for an infection after a root canal. There is no home remedy that can clear out an infected root canal.

Depending on how severe the infection is, the combination of treatments may differ. Here are all of the possible treatments that your dentist may perform for this condition:

  • Oral antibiotics. You may just need to take a round of oral antibiotics. This would be the simplest treatment because you don't need any physical procedures done.

  • Antibiotics inside canals. If the root canal isn't able to clean out the infection completely, you may need an antibiotic placed inside of the canals. This medication will be left in there for 7-14 days. You may need a few rounds of it if the infection is very severe. After everything clears up, your dentist can fill the canals.

  • Root canal retreatment. Perhaps the infection wasn't cleared out the first time around and all you need is to clean out the root canal one more time. Basically your dentist will redo the entire root canal procedure all over again.

  • Tooth extraction. If the infection is too severe and your dentist deems the tooth to be hopeless, it may be better to just have it taken out. Removing the tooth will definitively clear out the infection.

  • Drain the abscess. If there is severe swelling associated with the infected root canal, the abscess will need to be manually drained. This involves a lot of local anesthesia and popping the abscess. Once it pops, a mixture of pus and blood will come oozing out.

We just want to emphasize to you that treatment for this is a very physical process and you need a dentist to perform it for you. There is no way you can do this at home with any home remedies.

What causes a root canal to get infected again?

Unfortunately, there are multiple ways for a root canal to get infected. It may also be difficult for your dentist to detect and they may not show up until many years later.

  • Residual infection. There is no way to measure whether or not all of the bacteria within an infected tooth has been treated. We mostly assume that it is clear of infection after treatment because there is no test to do it. If an infection escaped by hiding away, it can repopulate and cause a problem in the future.

  • Missed nerve. Some teeth have multiple extra nerves. If you did the root canal and removed only the assumed number of nerves, extra ones may have been missed. These missed nerves will become infected and cause pain in the future.

  • New bacteria. The root canal could've been finished beautifully but sometimes a new infection can come along and attack the tooth. Unfortunately, there is no way to prevent this aside from keeping your oral hygiene as pristine as possible.

  • Trauma. If you sustain trauma to the tooth, it could fracture and lead to an infection. Examples may be from eating hard foods or sports related injuries.

molar with two extra nerves
molar with two extra nerves

This is an x-ray of a molar with two extra nerves. Most molars have three nerves on average with some having four. This particular molar had five nerves, which is very rare. If your root canal happened to have missed these two extra nerves, you could expect the tooth to get infected again at some point since it wasn't cleaned out completely.


Sometimes you may just be unlucky and end up with a reinfected root canal. However, you can try to minimize the chances of it happening by following these tips.

  • Maintain good oral hygiene by brushing at least twice a day for two minutes each.

  • Floss and use mouthwash prior to going to bed.

  • Minimize the amount of sugar in your diet so that the bacteria don't have fuel to work.

  • Go for your dental check ups every 6 months to treat small problems as promptly as possible.


Teeth that had root canals on them are not immune to infection. It is not a one time done deal. You still have to maintain good oral hygiene habits so that you can decrease the chances of it getting infected again.

If it does get infected, you can see our list of signs in order to give you an idea of if it was infected or not. Nonetheless, the best thing you can do is actually schedule a consultation with your dentist sot hat you can know for certain.

If something feels off, there is most likely something wrong with your tooth and it probably needs to be addressed. Don't wait on problems in hopes of them going away on their own because life doesn't quite work that way.



David Chen 200 x 200.jpg

About the author: Dr David Chen, DDS

Hello, I'm Dr Chen and I'm an actively practicing dentist in Long Island City, NY. I graduated from Columbia University College of Dental Medicine in 2016 but prior to going to dental school I was already working in the dental field. It's been more than a decade since I first got to know dentistry and let me tell you, time flies by quickly. Since then I've developed a fondness for writing, which is how this all got started!

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Medical Disclaimer:

This blog is purely meant for information purposes and should not be used as medical advice. Each situation in your mouth is unique and complex. It is not possible to give advice nor diagnose any oral conditions based on text nor virtual consultations. The best thing to do is to go in person to see your dentist for an examination and consultation so that you can receive the best care possible.

The purpose of all of this oral health information is to encourage you to see your dentist and to inform you of what you may expect during your visit. Due to the unfortunate nature of dentistry, there isn't really any true home remedies that will get rid of dental problems. Roughly 99.99% of them require in-person intervention by a healthcare professional.

Hint: That is the reason why you can't eliminate seeing dentists in your life!

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