Performing root canal on teeth that already 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? - pros, cons, issues and concerns.

Access
through
the crown.

Link to access cavity photo.

Crown
access
issues.

Link to diagram of access made directly through crown.

Root canal therapy is sometimes needed for teeth that have already had a dental crown placed on them. (The statistics on this page document that this is actually a fairly common situation.)

And in these cases, the question then becomes ... what happens to the crown when the tooth's root canal treatment is performed?

As an answer, we offer this page. Below we explain how the presence of an existing crown is handled, both during and after its tooth's root canal therapy, and what issues might become a problem or concern.

When a tooth already has a crown, the possible scenarios are:

  • Removing the crown before the treatment process (if possible) ...
  • ... Or performing the root canal work through the crown (making the procedure's "access cavity" directly through it).

 

In either, case after the tooth's treatment has been completed it must be decided if the crown can then be reused or if it must be replaced.


How a tooth's existing crown is managed during its root canal procedure.

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.

In our outline of the steps of root canal therapy, we explain how one of the first steps the dentist takes is creating an access cavity in the tooth. This is the opening through which they'll then perform its root canal work.
In the case where the tooth already has a dental crown, one of the following two scenarios will need to take place:

Option #1 - The dentist will remove the crown before making the access cavity.

When possible, this makes the ideal scenario. That's because:

Making the access cavity probably won't affect the fit of the crown.

The portions of a tooth that are trimmed away to make an access cavity are usually unrelated to those that affect a crown's fit and seal (discussed below).

So, following the tooth's work, the crown can simply be recemented back into place. All of the duties it provided for the tooth prior to its work can still be fulfilled.

Guidelines about restoring root canalled teeth.
Why this scenario may not be possible.
Unfortunately, as simple as this plan sounds, the reality of removing a crown from its tooth can be quite difficult (or even impossible) to do without damaging it or the tooth (discussed in more detail below).

So in most cases, a dentist will make an attempt at removal but will quickly move on to Option #2 if it doesn't seem to want to come off relatively easily.

Option #2 - The access cavity will be made through the existing crown.

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, the questions then arise: Has making the access cavity through the crown damaged 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.

Discussed below are the types of factors that must be considered when deciding between these two options.

Evaluating the condition of a crown after an access cavity has been made through it. - Issues and concerns.

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 the crown still strong enough to protect its tooth?

If the structural integrity (strength) of the existing crown has been compromised by the act of drilling a hole through it to make the access cavity, and therefore 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 has been weakened by making a hole in it will vary. Here are some of the factors involved:

a) The type of crown.

There are different types of crown construction, and the strength characteristics of each kind will be affected differently when a hole has been drilled through it.

All-metal crowns.

Drilling a hole through an all-metal crown (e.g. gold) probably won't significantly affect its overall strength and the level of protection it provides for its tooth.

Porcelain-fused-to-metal crowns.

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

But doing so may affect the integrity of its 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 the restoration placed as a repair for the hole, see "filling placement" below.)

More extensive porcelain fracture is possible too. In many cases, this may only be a minor cosmetic concern. But if the loss is large enough, it may create a problem with both appearance and function.

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.

Concerns about restoration strength and/or damage (such as microcrack formation) that may ultimately lead to failure are valid issues.

  • Just as with PFM crowns, ceramic chipping immediately around the access cavity itself is commonplace.

    (A study by Wood found edge chipping in 100% of ceramic crowns evaluated.)

  • Beyond that issue, the remaining strength characteristics of the perforated ceramic restoration will need to be considered suspect too.

    Logically, the amount of structural integrity that's lost will depend on the type of ceramic and fabrication method used. But unfortunately, the wide variety of techniques in use today make this a difficult subject to create general rules and guidelines about.

Section references - Wood

Our thoughts about the need to replace all-ceramic crowns that have had access cavities made through them.

High-strength dental ceramics.

It would be our interpretation of the articles that we've read that "milled" (monolithic) crowns using newer higher-strength ceramics (like zirconia) may retain the greatest level of strength after their root canal access cavity has been patched. (Bompolaki)

But the use of high-strength ceramics is a relatively new phenomenon in dentistry. And as such, it would be our guess that these types of restorations represent a relatively small percentage of all of the all-ceramic crowns in existence in patient's mouths, and therefore this point is not a viable argument for most cases.

Is adequate evaluation even possible?

We'll also mention that it caught our eye that the paper by Wood mentions that: "The visualization of crack formation on access (meaning the making of the access cavity) 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 simple visual inspection really be?

Section references - Bompolaki, Wood

b) The extent of the access cavity will be a factor too.

With this issue, it's not just how much of the crown's structure has been trimmed away (an issue that's primarily just a concern with all-ceramic restorations) but also how much internal tooth structure (that supports the restoration) has been removed.

It can be that when the root canal access cavity is created that the tooth is so hollowed out that it no longer provides a solid foundation for its existing crown.

(A study by Heydecke determined that simply filling in this type of extensive hollow space with dental restorative did not restore tooth strength.)

So with these types of cases, a new crown (with a more encompassing design and possibly a post and core) will need to be made.

Section references - Heydecke

2) Can the existing crown be inspected adequately?

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

  • A study by Abbot 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.

Section references - Abbott

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 ensure 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 dentist's 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 from its tooth in a fashion where it remains fully intact and undamaged can be exceedingly difficult, if not impossible. Despite a dentist's best and most careful efforts, it's certainly possible that the crown will be ruined.

Different types of crown construction may favor removal. For example, the brittleness of some types of all-ceramic crowns may make the success of this option unlikely whereas with an all-metal one a possibility. However, even the metal aspect of crowns can be damaged beyond repair during this process.

As an added peril, even the tooth itself might be damaged during the removal attempt, possibly even irreparably.

All of this means that while your dentist can be expected to make a try at removing your tooth's restoration, 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 the tooth's root canal treatment has been completed, they will evaluate it and its outlook as discussed on this page.

 
 
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 Page references sources: 

Abbott PV. Assessing restored teeth with pulp and periapical diseases for the presence of cracks, caries and marginal breakdown.

Bompolaki D, et al. Fracture resistance of lithium disilicate restorations after endodontic access preparation: An in vitro study.

Heydecke G, et al. Fracture strength and survival rate of endodontically treated maxillary incisors with approximal cavities after restoration with different post and core systems: an in-vitro study.

Wood KC, et al. Resistance to fracture of two all-ceramic crown materials following endodontic access.

All reference sources for topic Root Canals.

Comments

Reason not to reuse crown.

The opening in my existing porcelain metal crown seems small to me. Why can't my dentist just put a white filling in to fill it in and be done with it?

Jb

We're not necessarily saying that that can't be an option. But we can say that making a new crown has some advantages.

1) You state that your existing crown is a porcelain metal one (we're assuming you mean porcelain-fused-to-metal or PFM).

To access the interior of your tooth your dentist has had to drill a hole through its porcelain layer. That makes the porcelain inherently unstable and more prone to fracture. Probably in most cases this never becomes an issue but the potential is there.

While only cosmetic in nature, we'll also state that it's unlikely that the color of the filling placed will exactly match your crown. White filling material (dental composite) has some degree of translucency, which means that it will display some of the color of adjacent materials. In this case, it will have a grey tint due to the adjacent metal layer underneath the crown's porcelain surface.

2) The most important reason why a new fully intact crown makes the better choice is because of the seal it is able to create over the tooth (see our discussion above about coronal leakage).

When a filling is used to plug the hole, the quality of the seal it creates for the tooth is difficult to evaluate and monitor.

Probably the best thing that the dentist can do in this case is extend the filling down inside the tooth as far as they can (even down into the openings of the actual root canals). This way the filling's seal is as long as possible, thus creating the most substantial barrier possible.

If the seal is compromised, since your crown has a metal component that covers over the tooth there is no way for the dentist to monitor what's going on inside (like to check for decay) via x-rays.

All and all, predictability of its seal over the tooth is the main advantage that a new crown offers over just plugging the hole in the existing one with a filling.

Filling Material

Tooth #29 has a ceramic crown, with a bridge to #27, so I don't think replacing the crown is an option for me after the root canal. What is the most durable "white tooth bonding" filler material I could use for the access cavity? Thank you!

sb

Clearly this is an issue for your dentist to decide but in general terms:

Dental composite products (white filling materials) are manufactured using different formulations. Some of these are made specifically for applications, like restorations for back teeth, where compressive strength and wear resistance are needed.

So at least at the surface of your crown's opening, they will probably choose a "posterior" dental composite.

What they do inside the tooth is important too. If the filling isn't just all one piece, they'll need to make sure that any base materials underneath the restoration (filling in between the filling and actual tooth structure) have good compressive strength characteristics too, so it is adequately supported.

Tooth # 31 with crown

My current dentist said I have a r/c problem and need a new crown after they treat this tooth. My old dentist said it might be a broken tooth in there that is causing pain near the gum area. Either way pain is still there for almost a year and I'd like to know if they can put the same crown back in place if the middle tooth to be removed or treated for r/c?

Lea

We had trouble interpreting your comments but did notice that you've posted them on this page about reusing a crown after root canal treatment has been performed.

As discussed above, if the crown can't be removed for the root canal work and instead has an "access cavity" made through it, the most predictable/safest choice is to have a new crown made. But, per the arguments discussed above, you and your dentist might decide that patching the crown makes an acceptable alternative.

The other issues you discuss are simply one of diagnosis (which dentist is right about what is wrong). Seeking an evaluation from an endodontist often makes a good choice when difficult cases are involved.

Root Canal with a Crown

After a root canal has been performed that has a crown on the tooth, can I expect some pain and discomfort until the new crown is replaced.

GS

No. Generally that is not correct.

If for some reason the "bite" of the original crown is different than before, then yes that could irritate your tooth. But short of that, the issue of a crown, new or old, would probably have little to do with any near-term postoperative sensitivity you notice.

This page discusses common causes of post-root canal treatment sensitivity.

Don't need a root canal, just access to fix cavity?

Instead of replacing my crown, my dentist is going to attempt to make an access point through the crown to fix a small cavity tomorrow, then patch it like a chipped tooth. MA won't cover a new crown, but they will cover a filling. She might have to remove the old crown anyway if she runs into issues, but since I have Multiple Myeloma, no money and no income, I'm willing to give it a shot and see if it works for the amount of time I have left.

Anything I should be aware of, or keep an eye out for, if she is successful and doesn't have to remove the old crown?

Thanks

Logan

You don't really mention, so we'll assume that your crown is a porcelain/ceramic one.
The general difficulty associated with patching ceramic crowns is that the crown is a ceramic (glass) but the material used to make the repair is a plastic (dental composite/white filling material).

That offers a few challenges. One is, can a strong enough bond be created between the ceramic and plastic so it will stay in place. Also, the plastic won't have strength characteristics as strong as the ceramic. And finally, the plastic will tend to stain over time, whereas the ceramic will not.

With those difficulties in mind, you should respect your repair for what it is, a patch. You might favor the tooth somewhat, so to protect it from excessive biting or chewing forces.

If you can see the restoration, you might check for signs of deterioration over time (cracks, small bits chipping off at the edges, fracture, dark stain between the restoration and crown). Regular examination by your dentist would be ideal.

Drilling through different types of crowns

Hello. Thank you for this fantastic website. I have found the information to be very helpful. I’m afraid that I might need to have a root canal performed on a crown that was only placed a month ago. The dentist said at first that he was going to order me a crown made of zirconia, but then later referred to it as porcelain when he was putting it in. Does this suggest that it is some sort of hybrid? How will this crown hold up if I get a root canal performed by an endodontist (using smaller, more precise equipment)? Thank you for your time.

Chad

You'll probably have to ask to know for sure.

The best case for your situation is where your crown is a monolithic zirconia crown (a crown milled out of a single block of Zirconia ceramic).

Another type of "Zirconia" crown is one where only the portion of the crown that covers over the tooth is made out of Zirconia. Then on top of this another kind of "porcelain" is layered or pressed on so to give the crown its tooth-like shape. (This is referred to as a veneered Zirconia crown.)

As this paper describes:
Effect of endodontic access cavity preparation on monolithic and ceramic veneered zirconia restorations.

As compared to the veneered form, the monolithic construction form tends to be less damaged by the act of creating the access cavity through the crown.

--
An endodontist won't necessarily try to perform your root canal through a smaller access cavity, because having adequate access is key to the success of the procedure. But yes, their skills/equipment/dexterity may be such that they routinely tend to work through a smaller opening.

Also, an endodontist is more likely to know how large of an opening they actually do need. Or in the case of searching for difficult to find canals, be more effective in locating them without removing excessive tooth/crown structure.

* Comments marked with an asterisk, along with their associated replies, have either been edited for brevity/clarity, or have been moved to a page that's better aligned with their subject matter, or both. If relocated, the comment and its replies retain their original datestamps, which may affect the chronology of the page's comments section.


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