The root canal vs. dental crown relationship. -

Can a crown be placed without the tooth having had root canal treatment first? | If not, why do so many crowned teeth end up having it? | Statistics about the endodontic therapy vs. crown relationship.

A) Dental crowns vs. root canal treatment.

Some people seem to think that if a tooth needs a crown that it also has to have root canal therapy. To the contrary however, these are entirely separate procedures and most certainly one can be performed without the need for the other.

Having said that, there are some statistical relationships between the two. For example:

  1. A tooth that has had a crown placed is more likely to require root canal at some point (either in its near or distant future). - This is the main topic discussed on this page.
  2. The long-term success rate for teeth that have had root canal performed may be improved by placing a crown. - We discuss this issue here.

Dental research and statistics -

B) What is the relationship between crowned teeth and a need for root canal therapy?

Picture of root canal treatment being performed on a tooth that has a dental crown.

Root canal treatment being performed on a previously crowned tooth.

A number of studies have evaluated crowned teeth over the long term to see what type of events they tend to experience.

As we report below, it's commonplace that crowned teeth with no previous history of problems with their nerve (pulp) tissue ultimately develop complications that necessitate their having endodontic therapy.

Studies and their findings -

  • Bergenholtz (1991) found that on a long-term basis 9% of crowned teeth as opposed to only 2% of those without them required root canal treatment.
  • Felton (1989) found that 13.3% of crowned teeth required root canal treatment over the long-term as opposed to only .5% of teeth without restorations.
  • Whitworth (2002), who reviewed the above studies as well as a number of others, suggested that a realistic estimate might be that 4 to 8% of crowned teeth will require root canal treatment within the ten years that follow the restoration's placement.

    Tan (2004) placed this number at 10% (for previously vital teeth devitalizing over the next 10 years).

  • Cheung (2005) evaluated 122 teeth that received crowns that had no previous history of root canal treatment. At 10 years, 16% of the study teeth had experienced endodontic complications and at 15 years 18%.

    Valderhaug (1997) placed these numbers at 8% at 10 years, 13% at 20 years and 17% at 25 years.

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C) What causes crowned teeth to require root canal therapy?

You might wonder why the above statistical relationships exist. What is the cause?

1) Crowns aren't usually placed on pristine teeth.

For the most part, the answer lies in the fact that dental crowns are usually used to rebuild teeth that have experienced some type of significant structural damage. And as it happens, these same types of events can also insult or compromise the tooth's nerve tissue and therefore create a need for root canal treatment too.

Crowning vs. root canal.

The relationship between the two is a little bit like the similarity between automobile bodywork (= getting a crown) and under-the-hood work (= having root canal treatment).

  • If you're in an accident (tooth breakage) you will need bodywork (a crown).
  • If the accident has been especially severe and your radiator has been damaged too, then you will also need under-the-hood work (root canal treatment).
  • But the exact nature of the repair work required will simply depend on the extent of the accident that has occurred.

So, it's not that placing a crown has caused a need for endodontic therapy. But instead that the events that have led to the need for the crown have actually caused a need for both.

2) Your tooth's crowning procedure may have stressed its nerve.

If you think about the crowning procedure from your tooth's point of view, the process really is a big event.

What it entails.

During the procedure a drill is used to grind away essentially all of the tooth's enamel layer, and a fairly substantial amount of the dentin encasing its nerve (pulp tissue) too. Related to doing so:

  • The act of drilling creates friction and therefore heat that the dentist must then keep in check so the tooth doesn't become overheated. (That's why dental drills spritz a mist of water.) Anusavice (2007) suggests that the greatest risk of creating tooth trauma is heat generation during tooth preparation.
  • The drilling creates jarring vibrations that are transmitted throughout the tooth (physical trauma).
  • Because the dentin layer (the hard tooth structure that surrounds the tooth's pulp) is porous, the mechanical action of the dentist's drill can pump bacteria into this layer towards the nerve tissue, which can result in pulpal irritation.
  • Similarly, Anusavice (2007) suggests that the tooth's exposure to various chemicals used throughout the entire crowning process can result in trauma to its pulp tissue too.

The traumatic effects of each of the events mentioned above can act cumulatively. And the thinner the layer of dentin that exists between the surface of the crown preparation and the tooth's nerve, the more likely that the level of trauma created will be significant.

Isn't this reason enough not to have a crown made for a tooth?

No, if a crown is indicated, then that's the best plan. Yes, possibly the trauma of the procedure will, on its own, be the traumatic event that triggers the ultimate degeneration of the tooth's pulp tissue.

But if so, it's most likely that the procedure was simply the event that finally pushed the health of the compromised tooth's nerve over the edge. The crowning process precipitated the timing of an outcome that would have ultimately occurred anyway.

D) The timing of the need for root canal treatment can be quite varied.

There can be a lot of leeway as to when a crowned tooth's need for endodontic therapy finally becomes apparent.

  • It's possible that it may be during or immediately following the crowning process (days, weeks).
  • It's more likely that discovery won't occur until a later point in time. Many people go without noticeable symptoms for many years.
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The timing of events may seem suspicious.

When symptoms occur relatively sooner, it may seem that the crowning process itself has been the culprit. This can be true (for all of the reasons outlined above), but usually the tooth's procedure was not the original causative factor. Here's an explanation why.

Your tooth was probably worse off than realized.

Dental crowns are most frequently used to rebuild teeth that have experienced some type of structural catastrophe (crack, fracture, large cavity, lost filling).

And due to having experienced this traumatic event, it can be that the tooth's pulp tissue, while still able to survive, exists in a compromised state. (As in it's no longer as resilient as it once was and therefore isn't as able to healthily rebound from trauma or insult.)

While in this state, it's possible that some type of stimulus (such as the crowning procedure) will trigger the final degenerative process of the tooth's nerve, and its subsequent need for root canal treatment.

Should your dentist have anticipated this problem?

A history of your tooth being asymptomatic isn't conclusive evidence that all is well with its nerve. And while you can't expect your dentist to be all-knowing, there are routine tests that they should perform that may reveal a tooth's endodontic problems before its crowning procedure is begun.

Taking an x-ray.

As routine as taking a radiograph of a tooth is in preparation for its crowning procedure, when it comes to diagnosing endodontic problems an x-ray by itself often isn't conclusive.

What exists on the picture may be difficult to interpret. Or the tooth's condition may be at a stage where the types of changes visible on an x-ray have not yet developed.

Clinical testing.

It's generally accepted that thermal (cold) and electric pulp testing can provide a reasonably reliable estimate of the status of a tooth's nerve (Weisleder 2009, Jespersen 2014) and therefore they should be performed prior to the tooth's procedure.

  • Thermal testing involves placing/creating a hot or cold stimulus on your tooth's surface. For example, in the case of cold testing, a cotton swab soaked with a refrigerant, dry ice or just regular (water) ice may be used.

    It's generally expected that a healthy tooth will feel a sensation, and then once the stimulus has been removed or has dissipated the sensation will promptly fade away. Even teeth with existing fillings or crowns can usually be tested thermally.

  • Electric pulp testing (EPT) involves the use of an electric device that passes a low-level electric current to your tooth. It's expected that a healthy tooth will respond to this stimulus.

    If the tooth has an existing crown or filling, EPT is know to give false positive or negative responses.

Drawing a conclusion.

Despite performing these and even additional evaluations, the results of x-rays and clinical testing can be vague and difficult to interpret.

If collectively all signs tend to point to the same conclusion, then great. But without a clear consensus, a dentist will probably give the tooth the benefit of the doubt as opposed to performing root canal treatment without a clear indication.