Crown complications: The unexpected need for root canal treatment.

- Why does a crown / root canal relationship exist? | Statistics.

When a dentist places a dental crown on a tooth, it's no doubt their hope that doing so will be the last procedure that that tooth will require for a very long time.

Unfortunately, since crowns are not placed on pristine teeth but instead those that have been seriously compromised by fracture, breakage or the presence of tooth decay, complications can and do occur.

In some cases, it's possible that the same traumatic event that has caused the need for crown placement has also damaged or compromised the tooth's nerve tissue (pulp). If so, root canal treatment will ultimately be required.

Statistics: Crown placement vs. a tooth's need for root canal treatment.

Dental research has identified a statistical relationship between those teeth that have had a dental crown placed and those that subsequently require root canal treatment.

Relative to the time of crown placement, this need for root canal may become apparent either immediately, or else in the near or even very distant future.

Here are some of the statistics that dental studies have been reported.

  • Bergenholtz et al. (1991) found that over the long-term 9% of crowned teeth, as opposed to 2% of uncrowned ones, required root canal treatment.
  • Felton et al. (1989) reported that 13% of crowned teeth developed a need for root canal treatment over the long-term, as opposed to just one-half of a percent of unrestored teeth.
  • Whitworth et al. (2002) performed a review of available dental literature. They estimated that 4 to 8% of teeth that have had a dental crown placed will require root canal treatment within ten years.

What's the cause of this relationship?

Various scenarios can take place that ultimately lead to a tooth's need for root canal treatment. They include:

a) Inflammation triggered by trauma.

Any type of incident that causes tooth trauma (such as a blow that has fractured a tooth) can have a detrimental affect on the health of a tooth's nerve tissue (dental pulp). The reason for this is as follows.

  • When a tooth receives mechanical insult, its nerve tissue (just like any other type of soft body tissue) responds with what is called an inflammation reaction. A part of this reaction includes tissue swelling.
  • In the case of teeth, when this swelling occurs the pulp tissue is compressed (the nerve tissue expands due to swelling but is limited by the hard confines of the tooth). As the compressive forces build up, they restrict the flow of blood through those vessels that service and supply the nerve tissue.

Blood vessels perform vital functions that help a tooth's nerve recover from the trauma it's received. This includes the delivery of oxygen and nutrients, as well as carrying away the fluids that have caused the swelling.

The net effect is that the events that should take place to help the tooth's nerve tissue to recover are instead stifled.

What are the consequences?

In severe cases, the dental pulp will fail to recover and ultimately die. As a result, root canal treatment will be required. In lesser cases, the nerve may survive but linger on in a debilitated state. Root canal treatment may not be required for weeks, months or even years.

b) Bacterial insult.

Once bacteria and oral contaminates have reached a tooth's nerve tissue, it's quite likely that its degeneration will begin and root canal treatment will ultimately be required. Events that can lead up to this scenario include the presence of advanced tooth decay or possibly tooth fracture.

In many cases, the dentist has no way of knowing how much damage has occurred and can only make a repair and hope for the best. If required, the tooth's need for root canal treatment may become apparent immediately, in the near future, or possibly not for years to come.

How do these scenarios relate to crowned teeth?

Each of the above-mentioned events (tooth breakage, fracture or the presence of a large amount of tooth decay) can also be events that cause enough damage to a tooth that dental crown placement is required.

So, yes, there is a relationship between crown placement and the need for root canal therapy. But it's not that one has caused the other but instead that the precipitating event has caused a need for both (although the need for root canal treatment may not be diagnosed for months or years to come).

Should your dentist have anticipated this?

You might wonder why your dentist didn't anticipate your tooth's need for root canal treatment and mention it beforehand. To their defense, it's really impossible for them to be that all-knowing.

Dentists have tests that can help to evaluate the health of a tooth's nerve tissue. And it's most likely that these were performed (and you simply did not realize it) at that visit when your tooth's need for a crown was first evaluated.

Unfortunately, the results of these tests are often vague and difficult to interpret. And in those cases where collectively their conclusions are ambiguous, your dentist will most likely refrain from recommending root canal treatment for fear of performing an unnecessary procedure.