Coronal leakage - A cause of root canal treatment failure.

- What is it? / What causes it? / How can it be prevented? / Which types of restorations create the best seal?

Page Graphics | Animations.
Link to diagram of dental restoration leakage.
Link to picture of failed root canal.
Coronal leakage: What is it?

Dentists have become increasingly aware of a process termed "coronal leakage." This phenomenon involves the situation where bacteria and debris find a way to seep into and recontaminate the interior of a tooth that has previously had root canal therapy.

Why is this a problem?

Coronal leakage is a cause of root canal treatment failure. Once it has occurred the tooth will require endodontic retreatment, so to once again clean and then reseal the tooth's root canal system.

How is it prevented?

As this page explains, it's prevented by way of placing an appropriate permanent dental restoration for a tooth promptly after its root canal work has been completed.

A description of coronal leakage.

One of the goals of root canal therapy is the elimination of bacteria and other contaminates from within a tooth.

Bacteria seeping past an endodontically treated tooth's filling.

If the filling's seal is compromised, bacteria can recolonize the tooth's root canal system.

Now, imagine the situation where a tooth's treatment has been successful in accomplishing this task. But, over time, the same types of contaminates are able to leak back into the inner confines of the tooth.

If this occurs, the conditions inside the tooth will revert to those similar to what likely existed before its treatment was initiated. And as a result, what was successful treatment will ultimately fail.

That's what coronal leakage is.

This type of recontamination process is precisely what the term "coronal leakage" refers to.

An x-ray showing failed endodontic therapy as a result of coronal leakage.

Bacteria seeping past this tooth's defective filling has caused its root canal treatment to fail.

It's the phenomenon where oral debris and bacteria seep from the mouth, past a tooth's dental restoration, and penetrate into the tooth's treated root canal space.

The term "coronal" refers to the fact that the pathway of this seepage is via the "crown" portion of the tooth (the part of the tooth that lies above the gum line).

What research has found.

While the concept of coronal leakage has been known for over 100 years, it's only since the 1990's that it's received wide-spread attention and study.

Nowadays it's considered a significant factor in endodontic failure. But only one factor of several that may be involved. Here's an explanation.

Gillen (2011) [reference sources] applied statistical analysis to data collected from published studies. The findings of the report were:

  • Teeth having both adequate-quality root canal treatment and final dental restorations had a 2.8 greater success rate than teeth having adequate treatment and inadequate restorations.

But the study also determined that:

  • Teeth having both adequate-quality root canal treatment and final dental restorations had a 2.7 greater success rate than teeth having inadequate treatment and adequate restorations.

Together, these findings imply that:

  • Placing a suitable restoration can play an important role in protecting the outcome of a tooth's therapy.
  • But a well-sealing restoration alone can't overcome problems created by low-quality endodontic work (which only makes sense).

Recontamination can occur fairly rapidly.

Although a tooth's root canal system is sealed during its procedure (by way of placing gutta percha and paste sealer), the integrity of this seal can't resist the assault allowed by coronal leakage indefinitely.

  • Laboratory studies suggest that bacteria can recolonize the full length of an endodontically sealed (but not otherwise protected) root canal in as little as a few days. And the endotoxins they create (irritating molecular compounds) can do so at an even faster rate. (Eliyas 2015)
  • Torabinejad (1990) determined that the recontamination of a tooth's entire root canal system may occur in as little as 2.5 to 6 weeks.

Understanding how the potential for coronal leakage might affect your tooth's treatment.

An x-ray showing a tooth's completed endodontic treatment and a temporary filling.

Replacing a temporary filling promptly helps to protect your root canal work.

A) Coronal leakage as it pertains to temporary dental restorations:

Once your root canal therapy has been completed, your dentist will need to place some type of temporary restoration that will create a seal that protects your tooth's work until that point in time when a permanent one can be placed.

You need to be aware of the temporary nature of this restoration and the time frame over which it can be expected to maintain its seal. You'll need to ask your dentist for details but it may be as little as 3 weeks. (AAE 2002)

B) Coronal leakage as it pertains to permanent dental restorations:

Generally speaking, your tooth's permanent restoration should be placed as soon as is reasonably convenient (in other words, don't drag your feet on scheduling this procedure).

It's important to adhere to your dentist's instructions on this matter. Their recommendation will be based on the type of interim restoration they have placed in your tooth's access cavity and the time frame they feel they can rely on the seal it creates.

The restoration they place will need to:
  • Be capable of creating a barrier to seepage.
  • Be durable enough that this seal is maintained, even as the tooth functions under extreme conditions.
  • Offer protection for the tooth so the seal is not compromised due to tooth fracture.
The seal of a dental crown helps to prevent coronal leakage.

A dental crown can establish an excellent seal but not all root canalled teeth require one.

What types of restorations can meet these requirements?

After an evaluation, your dentist will make a recommendation as to what type of restoration they feel should be placed. (We discuss factors related to making this decision here: Rebuilding teeth after root canal treatment.)

Generally speaking, there are three alternatives that might be utilized.

  1. Placing a dental crown. - Without question, the fit of a dental crown over its tooth typically creates a superior, lasting seal. And for teeth that require strengthening/protection from fracture, placing one makes the right choice.
  2. Placing a filling. - Not all root canalled teeth require the protection of a crown. If after its endodontic treatment has been completed the tooth remains primarily intact, the placement of a dental filling (dental bonding or amalgam) has been shown to create an adequate seal. (Eliyas 2015)

    In most cases the type of teeth that meet this criteria would be those that previously had no, or just a minimal, dental restoration.

  3. Patch the tooth's existing crown. - In the case where a tooth's root canal work has been performed through an opening drilled through it's (existing) crown, it's possible that a satisfactory seal can be created by filling the tooth's access cavity with dental restorative (amalgam or bonding).
Which makes the best choice toward preventing coronal leakage?

In terms of creating a predictable, lasting seal, there is no question that placing a brand new dental crown makes an excellent choice. But doing so is too aggressive of a treatment for teeth that don't otherwise require this type of restoration (see "rebuilding" link above).

Choosing to patch an existing crown through which the tooth's root canal treatment has been performed makes the least predictable choice. We explain the reasons why here.


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