A Gum Boil Appeared After My Root Canal

Written & Reviewed by Dr David Chen

If you notice a boil on your gums after finishing your root canal, that is a tell-tale sign of a complication. It may look like an innocent pimple on the gums but it is actually an infection.

Do not brush it off as a mere coincidence because a complication must’ve occurred during the root canal treatment and you will need to address it. A trip back to the dentist is warranted and we will explain why you shouldn’t wait on this.

What is a gum boil?

A gum boil is NOT just a simple pimple on the gums because it is an oral manifestation of a periapical abscess.

Gum boil with sinus tract - drawing
gum boil with sinus tract

That pimple which you see on the gums is actually the orifice of a sinus tract that leads directly to the tooth abscess. That can be confirmed with a technique called gutta percha (GP) tracing, where your dentist inserts the GP directly into the boil. Then they take an x-ray to see where the gutta percha cone ends up. It usually stops at the location of the infection.

x-ray of gutta percha tracing
Gutta percha is the white line and you can see it ending at the root tip

In summary, the gum boil is not an ordinary pimple because it is a legitimate abscess, it won’t go away if you just wait.

Treatment for a boil on the gums

The interesting part of having a boil on the gums after a root canal is that the root canal is supposed to treat gum boils!

Yes, you read that correctly. Under normal circumstances, if you walk into a dental appointment with a gum boil, your dentist would recommend a root canal (RCT) for it. Typically after the RCT, the boil should go away within a few days or a week at most.

root canal steps diagram
steps for a root canal procedure – abscess heals afterwards

Basically, the procedure is meant to get rid of the infection so the abscess should resolve and thus the pimple goes away. However, if the boil shows up on the gums AFTER the root canal was completed, it means you have a complication.

Cause for the gum boil after a root canal

After the root canal has been completed, there should be no more infection. The fact that a gum boil appeared, it means that the abscess did NOT go away completely.

Reasons why infection escaped removal:

  • Bacteria hiding in accessory canals.
  • Tooth has extra nerve.
  • Tooth is fractured.

Accessory canals

When your dentist does your root canal, they are typically only able to clean out the main canals thoroughly and fill them. Unfortunately, the teeth may have accessory canals, which are small off-shoots which are near impossible to clean.

root canal - accessory canals
Credit: H. M. A. Ahmed, P. Neelakantan, P. M. H. Dummer

If bacteria are hiding in these accessory canals, they will most likely escape elimination and detection. If this is the case, despite completing the treatment, the infection will return because the bacteria can re-proliferate.

Note: It’s not that your dentist doesn’t want to clean/shape the accessories but rather it is impossible. Current endodontic technology does NOT have a good way of doing it. That is the extent of our technology at this point in time.

Extra nerve

Alternatively, the tooth could’ve had an extra nerve that may have been missed. As an example, most molars have 3 nerves but 50% of the time they can have 4 nerves. Most endodontists (root canal specialists) know to look for this potential additional nerve.

However, there are special situations where some teeth are like octopus where they have much more than just 4 nerves. The series of x-rays below demonstrate molars with 3, 4, and 5 nerves.

If a nerve was missed, you can bet that the abscess won’t go away. A pimple appearing on the gums would be expected.

Fractured tooth

Worst case scenario would be that the tooth is fractured.

In order to do the root canal, your dentist needs to drill a hole through the top of the tooth. Then they need to clean and shape the canals. Both of these actions remove tooth structure.

Sometimes there isn’t enough natural tooth structure left after completion of treatment. If you happen to bite into hard food the wrong way, the tooth can crack. For this reason, we do recommend that you try to get a crown on it as soon as possible to protect it.

What you should do about this

Now that you understand that a boil on the gums after a root canal is a tooth abscess, it cannot be left untreated. You will need to return to your dentist to have it addressed, it will either be a root canal retreatment or a tooth extraction.

Here is what you can probably expect depending on your specific condition.

gum boil after root canal - decision tree
Decision tree for what to do

Root Canal Retreatment

If the root canal needs to be re-done, it is called a retreatment. It will feel like deja vu all over again because the procedure is being repeated. The only difference is that the old root canal filling will need to be removed and you’ll most likely have antibiotics placed inside the canals.

What to expect for a root canal retreatment:

  1. Administer local anesthetic to numb the tooth.
  2. Place rubber dam on the tooth for isolation.
  3. Drill through the top of the tooth.
  4. Remove old root canal filling material.
  5. Locate missed nerve and clean it out.
  6. Place antibiotics inside the tooth.
  7. Close up the tooth with a temporary material, Cavit G.
  8. Wait 1-2 weeks before returning to dentist.
  9. Open tooth back up and clean it out again.
  10. Permanently fill the root canal once more.
  11. Return to your restorative dentist for a core build up and crown.

Just so that there are no surprises, the cost for a retreatment will be more than the initial root canal therapy.


If the pimple on the gums is due to a fracture then the tooth cannot be saved. The next step would be to have the entire tooth removed via an extraction.

What to expect for the procedure:

  1. Administer local anesthesia, numbing gel followed by Lidocaine injection.
  2. Release gingiva and PDL fibers with a periosteal elevator.
  3. Elevate and luxate the tooth with an elevator.
  4. Extract the tooth with forceps once it is loose enough.
  5. Place gauze in mouth to stop bleeding.

The tooth removal process is fairly straightforward as you can see since it was described in 5 steps. Nothing to be afraid of, your dentist will take care of you.


Unfortunately if you’ve suddenly got a boil on your gums even though the tooth has been root canal treated, you will need additional treatment. That pimple isn’t as innocent as it seems because it is technically an abscess.

There are multiple treatments available but it’ll depend on the cause of the boil. If it has a favorable prognosis you can save the tooth with a root canal retreatment but if it isn’t favorable, you’ll need it extracted. You won’t know which one you need until you get a proper diagnosi by your dentist.


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