Coronal leakage - A cause of root canal treatment failure. -

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 it a problem?

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

How is coronal leakage 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 the phenomenon of coronal leakage.

The scenario.

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

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 that were originally associated with its problems are once again able to leak back into its interior space.

Once this occurs, the conditions inside the tooth will revert back to those similar to what existed before its therapy was performed. And as a result, what had been successful treatment will now ultimately fail.

That scenario describes what coronal leakage is.

Coronal leakage is the phenomenon where oral debris and bacteria seep from the patient's mouth, past an endodontically treated tooth's dental restoration, and ultimately penetrates into and recontaminates its interior root canal space.

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

The term "coronal" refers to the fact that the entry of the seepage is via the "crown" portion of the tooth. (The part of the tooth that's visible 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.

How big of a problem is it?

Nowadays it's considered a significant factor in endodontic failure. For example, a study by Hoen evaluated 337 failed root canal cases and determined that 13% of them involved complications with coronal leakage.

But with cases it may be only one factor of several that are involved. Here's an explanation.

A study by Gillen applied statistical analysis to data collected from published research. 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. (Inadequate restorations allow coronal leakage to occur.)

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 receives an "endodontic" sealed during its procedure (by way of the dentist placing gutta percha and paste sealer), the integrity of this seal won't be able to resist the continued assault of contaminates that's allowed by coronal leakage indefinitely.

Research findings.

The following two studies investigated how quickly a tooth's endodontic seal is compromised when it doesn't have the protection of any type of coronal restoration (like a filling or dental crown). This would be similar to the situation where a (failed, defective or inadequate) restoration was allowing coronal leakage to occur.

• A study by Torabinejad determined that the recontamination of a tooth's entire root canal system may occur in as little as 2.5 to 6 weeks.
  
• A more recent study by Eliyas found that bacteria can physically recolonize the full length of a tooth's sealed root canal system in as little as a few days.
  

  Even worse, this same study determined that endotoxins, irritating molecular compounds produced by bacteria, can cause recontamination at an even faster rate than the microorganisms themselves.

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

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 (that will be based on the type of temporary filling material that has been placed) but it may be as little as 3 weeks. (AAE)

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.

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.

Last revision/review: 12/27/2018 - Revised with content added.

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