Failed Root Canals On X-rays, What To Do?

Written & Reviewed by Dr David Chen

The purpose of a root canal procedure is to eliminate infection but that does not preclude it from future infections or procedural failures. What we’re trying to say is that the success rate is not 100% because root canals can fail and do fail.

tooth abscess

If it fails, one of the tell-tale signs is by taking a periapical x-ray of the tooth. These unsuccessful teeth tend to have their own unique characteristics on radiographs.

Signs of failed root canals on x-rays

Depending on the cause of the root canal failure, each condition will look differently on the x-ray. They each have distinct radiographic characteristics that separate them from one another.

Four common radiographic signs of failed root canals:

  • Halo surrounding the root of the tooth.
  • A short obturation meaning root canal filling material doesn’t reach the root tip.
  • An unfilled canal in a root canal treated tooth.
  • Perforation through the root or furcation of the tooth.

These unique appearances on x-rays is one of the ways that your dentist uses to tell if you’ve an endodontic failure. We will provide sample x-rays of what they look like below so you can compare it to how yours look.

Halo around the root

The most obvious sign of a failed root canal is a dark halo surrounding the root tip. It looks like a big dark circle which encompasses the tip of the root canaled tooth on an x-ray.

x-ray of tooth with halo around root after root canal - outlined

The radiolucent halo implies that there may be a recurrent infection or a possible tooth fracture. There is often an accompanying pimple on the gums that may be clinically present.

  • Recurrent infection. Despite completing the root canal which is meant to remove infection, it does not make it immune to future infections.
  • Tooth fracture. Alternatively, the halo could mean a fracture within the tooth. The prognosis for this condition is much more severe than a recurrent infection because treatment requires an extraction.
Failed root canal on front tooth

Short obturation

A root canal obturation which is short may also be an indication of root canal failure. What that means is when the root canal filling material is NOT filled all the way to the root tip. That may imply that the infected nerve was not completely removed or cleaned out.

x-ray of failed root canal with short obturation

The x-ray above shows what a short obturation looks like. Essentially the white radiopaque line inside the tooth is the gutta percha (filling material). However, the gutta percha does not extend to the apex of the root.

If there is still infection left within the tooth, wouldn’t you consider that as a failure? Certainly not a success by any means!

Missed canals

A missed canal can be a source of root canal failure. If an entire canal was missed, you can be sure that a lot of infection was left behind because it was never treated.

x-ray of missed canal - mb2 - styleitaliano
Credit: Dr Mohamad Za’frany

In the x-ray above by Dr Mohamad Za’frany, you can see how an entire tooth root was completely missed during treatment. Consequently the canal inside of that missed root was also left untreated.

According to studies, approximately 18% of endodontically treated teeth had missed canals.

  • Upper first molars had a 40.6% miss rate.
  • Endodontic failure was present in about 90% of the teeth with missed canals.

Despite these disheartening statistics, with the improvement in dental microscope technology, the casualties have been decreasing. Being able to zoom in multiples of what the naked eye can see has reduced some of the incidences.

Root perforation

Sometimes the root can be perforated either during the root canal procedure or during the restorative phase. What that looks like radiographically is a radiopaque object going in the wrong direction, often out of line with the canals.

x-ray of root perforation - root canal failure
Credit: S. Mohammed Saed, M. P. Ashley & J. Darcey

As you can see in the x-ray above, the big white post is going out through the side of the root thus perforating it. That is not the direction its supposed to go in. It’s supposed to follow the root canal filling material straight down towards the root apex.

Essentially, the tooth has been punctured and perforated. There is literally a hole in a place that should not have one.


If you see or are told that you’ve a failed root canal, you will need treatment for said tooth. Depending on why it failed, the treatment will differ.

Potential treatments for unsuccessful root canals:

  • Root canal retreatment. If the tooth is not fractured, your dentist may attempt to retreat it by redoing the root canal. This is the most conservative treatment option.
  • Apicoectomy. If the tooth has already been retreated once before, the next option would be an apicoectomy. This procedure will surgically remove the tip of the tooth root in an attempt to eliminate the infection.
  • Tooth extraction. For teeth that are fractured or have unsuccessful retreatments, an extraction is the only option left. After the tooth has been removed you can replace it with a dental implant.

Ideally you’d want to avoid losing your tooth but if it needs to be removed, it should be done. You can’t pick and choose what treatment you want because it all depends on what caused the root canal procedure to be unsuccessful.

Consequences of no treatment

We do not recommend leaving a failed root canal without treatment because that is akin to leaving an infection unattended. The bacteria will proliferate and eventually cause a tooth abscess.

Tooth Abscess Stages
Tooth Abscess Stages

These untreated abscesses will progress through the stages of a tooth abscess and progressively get more severe. Excruciating pain and facial swelling will ensue when left alone.


Root canals do not have a 100% success rate and they can fail. When they do, they will have a distinct radiographic presentation. Being able to identify what they look like on x-rays can tell you if you need further treatment for your tooth.

Hopefully yours hasn’t failed but if it did, at least now you know. However, you shouldn’t be averse to endodontic treatment because there are many which last decades without having problems. You may have just been unlucky this time around.


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