Performing root canal on teeth that have a crown.

- What happens to the crown? - Working through it vs. removing it. / Can it be reused or does it have to be replaced?

Page Graphics | Animations.
Link to access cavity photo.
Link to diagram of access made directly through crown.

Root canal therapy is sometimes needed for teeth that already have a crown on them. (Actually, like the statistics on this page document, this is a fairly common occurrence.)

What happens to the tooth's crown when root canal is performed?

This page explains how an existing crown is handled both during and after its tooth's root canal therapy is performed. The possible options are:

  1. Removing the crown during the treatment process (if possible).
  2. Performing the root canal work through the crown (drilling an "access cavity" directly through it).

After treatment, deciding if the crown can be reused or if it must be replaced.

Managing an existing crown during root canal treatment.

The access cavity through which endodontic therapy is performed.

An "access cavity" drilled through a tooth's crown portion gives the dentist entry to its nerve space inside.

As explained in our outline of the root canal procedure, one of the first steps a dentist takes is creating an access cavity in the tooth. This is the hole through which its root canal work will be performed.

In the case where the tooth already has a dental crown, one of two scenarios must take place:

Guidelines about restoring root canalled teeth.

Option #1 -

If possible, the dentist will remove the crown before drilling the access cavity. In practice however, removal is often much easier said than done.

Option #2 -

If the dentist determines that the crown won't come off (or at least not easily or predictably), then they'll have to drill the hole (access cavity) right through it to perform the treatment (see picture below).

The access cavity for the tooth's treatment has been made right through the crown.

A dental crown with an access cavity drilled through it.

If a hole is drilled, what's the outcome for the crown?

If this option is chosen, you may wonder: Does making an access cavity through the crown damage it? Can it still be used afterward or will it need to be replaced?

These questions are the subject of the remainder of this page. And as you'll discover, the answer is typically:

  • It may be possible to reuse the crown.
  • But it's probably a better plan to go ahead and replace it.

Listed below are the types of factors that must be considered when making a decision between these two approaches.

Evaluating the condition of a crown after root canal has been performed through it.

A dentist may make the access cavity right through the dental crown.

Drilling an access cavity through an all-ceramic crown will likely weaken it.

1) Is it still strong enough to protect its tooth?

If the structural integrity (strength) of the existing crown has been compromised by the act of drilling through it to make the access cavity and it can no longer be relied upon to protect the tooth (strengthen it, prevent fracture), it will need to be replaced.

Issues that must be considered.

In practice, the degree to which a crown is weakened by making a hole in it will vary.

a) The construction type of the crown is an important factor.

There are several types of crown construction, and the strength characteristics of each kind will be affected differently when it is drilled through.

All-metal crowns.

Drilling a hole through an all-metal (gold) crown probably won't significantly affect its overall strength characteristics.

Porcelain-fused-to-metal crowns.

Creating an access cavity through a PFM restoration likely won't significantly affect its overall strength either.

But doing so may affect the integrity of it's porcelain covering (outer shell), possibly resulting in chipping or fracture especially in the region immediately around the access cavity. (This chipping effect could compromise the integrity of a restoration placed later as a repair for the hole, see "filling placement" below.)

More extensive porcelain fracture is possible too. In some cases this may only be of cosmetic concern. But if the loss is large enough it may present a functional problem too.

All-ceramic crowns.

In comparison to types of crowns that contain metal, the process of creating an access cavity through an all-ceramic ("porcelain") one presents the least predictable outcome. Doing so can result in serious concern about restoration strength or damage (such as microcrack formation) that may ultimately lead to failure.

  • Just as with PFM crowns, ceramic chipping immediately around the access cavity itself is commonplace. [Wood (2006) found edge chipping in 100% of ceramic crowns evaluated.]
  • Beyond that, the overall strength of patched ceramic restorations evidently (and logically) depends on the type of ceramic and construction method involved, which makes this a difficult subject to create general rules of thumb about.

It would be our interpretation of the articles we've read that "milled" (monolithic) crowns using newer higher-strength ceramics (link) may retain the greatest level of strength after their root canal access cavity has been patched (Bompolaki 2015). However, it would be our guess that these types of restorations represent a relatively small percentage of all all-ceramic crowns placed to date.

It caught our eye that a paper by Wood (2006) stated that: "The visualization of crack formation on access (..cavity creation..) should assist the clinician in the decision to remake the crown." Our question would be that on a practical level, how thorough, definitive and predictable can this type of clinical evaluation be?

[page references]

b) The size of the hole will be a factor too.

With this issue, it's not just how much of the crown's structure has been trimmed away (which is likely the biggest concern with all-ceramics) but also how much internal tooth structure that supports the restoration has been removed too.

It can be that when creating the root canal access cavity that the tooth is so hollowed out that it no longer provides a solid foundation for its existing crown. [Heydecke (2001) determined that simply filling this additional hollow space in with dental restorative did not restore tooth strength.]

If so, a new crown (with a more encompassing design and possibly a post and core) will need to be made.

2) Can the existing crown be inspected adequately?

Despite both clinical and x-ray evaluation, a dentist's interpretation of the status an existing crown may not be accurate.

  • A study by Abbot (2004) examined 245 teeth both before and after their dental crown was removed.
  • Its findings were that 56% of the time tooth decay, cracks or other defects were not detected during the tooth's initial evaluation.
Placing a filling in an access made through a dental crown.

Sealing a crown's access cavity with a filling has both advantages and disadvantages.

3) Can reusing the original crown create an adequate seal for the tooth?

If the structural integrity of the perforated crown seems reasonable, the dentist may simply repair it by way of placing a dental filling (such as a bonded dental amalgam restoration for all-metal crowns or white tooth bonding for ceramic ones).

The benefit.

This solution is a very cost-effective one, in the sense that a repair is made simply and quickly for just the price of a filling as opposed to a new dental crown. However, there are concerns with relying on this type of patch.

The problem.
Coronal leakage - A situation where bacteria seep past a filling.

If the integrity of the filling's seal is lost, bacteria can recontaminate the tooth's root canal system.

The biggest concern when this route is taken is if the patchwork filling can create an adequate seal. One that will help to insure the long-term success of the tooth's root canal therapy by preventing coronal leakage (a process where bacteria and debris seep back into the tooth's root canal space).

This phenomenon is increasingly becoming understood as a significant contributor to root canal treatment failure. If this is the plan for your tooth you owe it to yourself to at least read our linked page above.

What's needed.

To be successful, the integrity of the barrier seal that the filling creates must not only be substantial but also lasting and predictable.

Unfortunately, these characteristics can be difficult to foretell and/or monitor with this type of patchwork situation. If recontamination occurs, root canal retreatment is indicated.

A dental crown provides an excellent seal for a tooth that has had root canal treatment.

Dental crowns are known for creating effective, lasting seals for completed root canal treatment.

Which makes the best choice after root canal, crown patching or replacement?

The alternative to patching an existing crown that's had root canal treatment performed through it is to just go ahead and make a new one. And this solution probably offers the greatest level of predictability and longevity.

If the amount of time, effort and money involved with placing a new restoration are of limited concern (which we admit never are), it seems likely that almost any dentist would consider placing a new crown the superior choice.

It may be possible for your dentist to remove your crown before performing your endodontic treatment.

Removing a tooth's dental crown before its root canal therapy is performed, and then recementing it afterward, can be an excellent plan. However, as ideal as this process sounds the practical application of this approach can be quite taxing, both for the dentist and patient alike.

Advantages of crown removal.

a) The integrity of the crown is preserved.

In the case where the crown can be removed fully intact and undamaged, there's a good chance that it can be permanently recemented after your root canal treatment has been completed. If so, that makes for a very easy and cost-effective solution.

b) Removing the crown aids your dentist's work.

The new shape that a dental crown can give a tooth can mask its original anatomy and orientation, to the point where interpreting the location of the root canals within can be difficult. If so, the dentists efforts to identify and access the canals may result in the removal of excessive amounts of tooth structure or even result in tooth damage.

When the tooth's crown is removed, it lessens the likelihood of these complications.

Taking off a crown prior to root canal treatment is often easier said than done.

Removing a crown in a fashion where it remains fully intact and undamaged can be exceedingly difficult if not impossible. Despite a dentist's best efforts, during the attempt it's still possible that the crown will be ruined or worse yet the tooth damaged too, possibly significantly so.

That means your dentist may at first try to remove your restoration. But if it doesn't come off easily with their initial efforts, they will likely back off on this approach fairly quickly. If so, they will then go ahead and drill an access cavity right through the crown. Then, after treatment has been completed, they will evaluate it and its outlook as discussed above.


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