The telltale signs of failed root canal with X-ray pictures

Root canal therapy is a highly effective procedure with a high success rate. It saves the tooth and keeps it in the mouth as long as possible. Studies have consistently shown a remarkable survival rate of root canal treated teeth, of up to 97%, even after 8 years of follow-up.

However, there are instances where the tooth may not fully heal, resulting in failure. Perhaps the sign that prompted you to seek answers about your root canal treatment is pain and discomfort.

In this article, we'll discuss the telltale signs of root canal failure with X-ray pictures, the common causes behind it, and the options available to you to save the tooth.

Telltale signs of root canal failure:

If you have undergone a root canal procedure, it is essential to know the signs of failure to spot them and prevent further complications. Here are the telltale signs to watch out for:

1. Persistent pain after the procedure:

After a root canal treatment, it is common to experience slight to mild pain, but it should gradually subside within 5-7 days. However, if you experience severe and persistent pain that lasts longer than expected, it may indicate a problem. In that case, you should visit your dentist immediately to assess and address the issue.

Possible causes of persistant pain:

While pain after root canal treatment can be a sign of healing, it can also indicate an underlying problem. Here are some of the possible causes:

1. Infection:

A tooth with root canal treatment is not immune to infection. It can occur even several months or years later. It could be due to a poorly adjusted root canal filling or a delay in placing a crown or restoration on the tooth. In this case, saliva and oral bacteria can make their way into the tooth, grow silently, and eventually cause an infection.

On the other hand, the infection that occurs a few days after the procedure is known as a flare-up. It is a very painful complication due to the persistence of bacteria in the root canals. It requires emergency treatment to avoid further complications.

2. Poor root canal filling:

A poorly adjusted filling is either too short or extends beyond the root tip. Both situations can disrupt healing and lead to root canal failure.

In the first scenario, you may not feel any immediate pain. But it is only a matter of time before bacteria grow in these empty spaces, leading to infection later on.

On the other hand, if the filling material extends beyond the root tip, your tooth may hurt on the first day of treatment. This is because the materials used are considered foreign bodies. When they overflow the root canals, they can react with the tissue and cause irritation, inflammation, and pain.

3. Missed canal:

If your dentist misses a canal during the root canal treatment, the infection may persist, leading to treatment failure. This is more common in molars with multiple roots, where one or more canals may be challenging to locate.
On the x-ray, the untreated canal appears as a thin dark line as it is not yet filled.

4. Instrument fracture:

Thin, sharp endodontic instruments help shape and clean the infected canals. During the procedure, a tool may fracture inside one canal, preventing complete access and cleaning. This may result in persistent pain, infection, and root canal failure.

5. Root perforation:

Root perforation is a hole in the root that can occur during the root canal procedure. It can cause sudden pain and bleeding during and after the procedure. If not detected and addressed, the filling material may come out of the canal through the hole, leading to failure.

6. Root fracture:

Root canal treatment can weaken the tooth and make it susceptible to breakage. One of the most common injuries to endodontically treated teeth is root fracture. If you feel pain when biting or chewing or have an abscess around the tooth, it may indicate a root fracture and require further treatment.

2. Swelling after root canal therapy:

It's not uncommon to experience some swelling following root canal therapy. In fact, it's a normal part of the healing process as your body works to fight off any remaining infection and repair the damaged tissues. However, if the swelling doesn't subside or is accompanied by other symptoms such as severe pain, pus discharge, or fever, it may be a sign of an infection and root canal failure.

3. Gum abscess or boil near the treated tooth:

The reappearance or persistence of a gum abscess or boil near the treated tooth is a sign of root canal treatment failure. This can occur when bacteria from the infected root canal spread to the surrounding gum tissue, causing an abscess or boil to form. Symptoms may include pain, swelling, redness, and pus discharge.

On X-ray, the abscess appears as a dark halo around the root tip.

How do you know if the tooth has healed properly?

When it comes to determining whether your root canal treatment has been successful or not, there are two main things we look for.

The first is that your tooth is asymptomatic, meaning that you don't feel any pain or discomfort in the area around the tooth.

The second thing we look for is the shrinkage or disappearance of the dark halo around the root tip on an X-ray. This indicates that the bone is regenerating, which is a sign of healing. But just because you're not feeling any pain doesn't necessarily mean that your treatment has been successful. It's possible for an asymptomatic infection to be developing around the root tip, and the only way to detect this is through an X-ray.

If left untreated, this infection could flare up and cause severe pain down the road. That's why it's important to schedule follow-up visits with your dentist, usually every six months after treatment, so that they can monitor the healing process and detect any complications early.

Can a tooth with a failed root canal be saved?

If you've had a root canal in the past and are now experiencing symptoms such as pain, swelling, or sensitivity, your root canal may have failed. But don't worry, there are ways to save the tooth.

The first option is root canal retreatment, which involves removing the old filling material, cleaning the canals, and refilling them with new material. This procedure can address any issues that may have led to the previous root canal failure and can give your tooth a second chance at healing.

In cases where retreatment is not enough to address the issue, an apicoectomy or surgical endodontic treatment may be recommended. This procedure involves removing the tip of the tooth root and any infected tissue, followed by a filling to seal the end of the root. It's a more invasive procedure than retreatment, but it can be effective in saving a tooth that would otherwise need to be extracted.

When is extraction the last option?

We always strive to preserve natural teeth whenever possible. However, in some cases, extraction may be necessary. This can happen if the tooth is severely damaged or if retreatment was not able to save the tooth. The most common situations include:

• The tooth cannot be restored properly: If the tooth is too damaged or weakened, it may not be able to support a crown or filling. In this case, extraction may be the best option to prevent further damage to the surrounding teeth and gums.


• Root fracture: This injury can occur during or after root canal treatment, and unfortunately, it can be difficult to repair. If the fracture is severe, extraction may be the only option to prevent infection and further complications.


• Advanced gum disease: Gum or periodontal disease can also lead to tooth extraction. As gum disease progresses, it can cause the bone that supports the tooth to resorb. This can cause several complications, such as loosening, tooth loss, and abscesses.