Performing root canal therapy on teeth that have crowns.

- What happens to the crown? - Removing it. / Working through 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 have already had a crown fitted. In fact, this is a fairly common occurrence.

This page explains how the crown is handled both during and after the tooth's treatment. The issues involved are:

The situation.

The access cavity through which endodontic therapy is performed.

As explained in our outline of the root canal procedure, one of the first things a dentist does is create an access cavity. This is the hole through which the tooth's work will be performed.

If the tooth already has had a dental crown placed, one of two scenarios will have to take place.

A) If possible, the dentist will remove the crown before creating the access. In practice, however, this is often easier said than done.

B) If the dentist determines that it won't come off (or at least not easily or predictably), then they'll have to drill the hole right through it.

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

What's the outcome for the crown?

If the latter case is chosen, a patient may wonder what will become of their tooth's crown. Will it be damaged? Can it still be used? Will it need to be replaced?

As explained on this page, the answer is typically yes, it can possibly be reused. But it's probably a better choice to go ahead and replace it. Listed below are several of the factors that must be considered when making this determination.

Issues of concern.

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

1) Will it still be strong enough to protect the tooth?

Clearly if the structural integrity (strength) of the crown has been compromised and it can no longer be relied upon to protect the tooth from fracture, it will need to be replaced.

In practice, the degree to which a crown has been weakened by drilling the access opening through it will vary.

The size of the hole will be a factor, as well as the type of material from which it has been made. (Related page: Dental crowns: Types & Construction.)

a) Crowns that contain metal.

Drilling a hole through an all-metal (gold) or porcelain-fused-to-metal crown may not significantly affect its strength.

b) Ceramic crowns.

In comparison, creating a hole through some types of all-ceramic (all-porcelain) crowns may very well weaken them, possibly significantly.

Other factors.

It might be that the act of creating the access cavity has created significant changes with the tooth itself.

Possibly it is now so hollowed out that it no longer provides a solid foundation for the original crown. If so, a new one (with a more encompassing design and possibly a post and core) will need to be made.

Placing a filling in an access made through a dental crown.

2) Will reusing the original crown create an adequate seal?

If the structural integrity of the existing crown seems reasonable, the dentist may complete its and the tooth's repair by way of placing a dental filling (dental amalgam or dental bonding).

This solution is a very cost-effecting one, in the sense that a repair is made for the price of just a filling (as opposed to new dental crown). However, there are concerns with this type of patch.

Creating a suitable seal is important.

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

One of the most important considerations is whether or not the filling can create an adequate seal for the tooth. One that will help to insure the long-term success of the root canal therapy by preventing coronal leakage (a contributor to root canal failure).

The difficulty in creating a substantial, lasting and predictable seal would be the major criticism of the crown/filling patchwork solution.

This may be more of an issue for back teeth, which have a constant exposure to heavy chewing forces, than front ones.

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

Which makes the best choice, patching or replacement?

The alternative to patching the existing crown 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 no concern (which, we admit, is never the case), 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.

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

Removing a crown is often easier said than done.

A crown can be exceedingly difficult to remove from its tooth, and it's possible that it will be damaged in the process. As a worst-case scenario, the tooth itself might be damaged, possibly significantly so.

That means that if it doesn't come off easily initially, the dentist will probably back off this approach promptly.


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