Dental crown complications:
A tooth's unexpected need for root canal treatment.

A) Will placing a crown on a tooth cause it to need endodontic therapy?

Dental crowns do not cause teeth to need root canal therapy but there is a relationship between the two, in the sense that (statistically speaking) a tooth that has had a crown placed on it is more likely to require endodontic treatment at some point in the future.

Dental researchers have attempted to quantify this association:

  • Bergenholtz et al. (1991) - found that on a long-term basis 9% of crowned teeth as opposed to 2% of uncrowned teeth required root canal treatment.
  • Felton et al. (1989) - Found that 13.3% of crowned teeth required root canal treatment over the long-term as opposed to only .5% of unrestored teeth.
  • Whitworth et al. (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 their placement.

B) Why will some crowned teeth require root canal therapy?

You might wonder why the above-mentioned statistical relationship exists. For the most part, the answer lies in the fact that dental crowns are used to rebuild teeth that have experienced significant structural damage. And, as it happens, these same types of events can also damage a tooth's "nerve" (dental pulp) and therefore create a need for endodontic treatment too.

It's not that placing the crown has caused the need for the endodontic therapy but instead that the events that have lead to the need for the crown have actually caused the need for both.

The timing of the needed root canal treatment can be quite variable.

There can be a lot of variability as to when the need for the root canal therapy finally becomes apparent. In many situations it will be obvious before any dental work is begun or, less frequently, during or immediately following the crowning process. In other cases, the need may not become evident until a later point in time, possibly even many years later.

The timing of events may seem suspicious to you.

In some instances, the case might be made that the crowning process has precipitated the need for the root canal treatment. This might be but, in general, it's typically not the original causative factor. Here's an explanation.

Dental crowns aren't used to repair pristine teeth but instead those 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 has been able to continue to survive, although in a compromised state. (Meaning it is no longer as resilient as it once was, in the sense that it is no longer able to healthily rebound from trauma or insult.)

While in this state, at some point in time, it's possible that some type of stimulus (including the process of placing a crown) will trigger the final degenerative process of the tooth's "nerve," and its subsequent need for root canal treatment.

C) How might placing a dental crown stress a tooth?

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

  • A drill is used to grind a way essentially all of a tooth's enamel layer, and a fairly substantial amount of dentin too.
  • This drilling process involves friction and the accompanying heat that it produces.
  • The drilling creates jarring vibrations that are transmitted throughout the tooth.
  • And because the dentin layer (the hard tooth structure that surrounds the tooth's pulp) is porous, the mechanical action of the drill can pump bacteria into this layer towards the "nerve" tissue, thus causing pulp irritation.

Each of these separate events has the potential to traumatize the tooth to some degree. And the thinner the layer of dentin that exists between the surface of the crown preparation and the tooth's pulp, the more significant the effects of these events can be.

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

No, if a crown is indicated, then that is the best plan. Yes, possibly the trauma of making a crown could, on its own, be the traumatic event that has triggered the degeneration of the tooth's pulp tissue. But much more likely the crowning experience has simply been the last event that finally pushed the health of the tooth's "nerve" over the edge. The crowning procedure precipitated the timing of an outcome that would have ultimately occurred anyway.

D) Should your dentist have anticipated this problem?

You can't really expect your dentist to be that all-knowing. And, as we stated earlier, dental crowns aren't placed on pristine teeth. They are used to rebuild teeth that have already received serious insult.

There are tests that a dentist can perform so to evaluate the health of a tooth, and typically a dentist will perform them before beginning the crowning procedure. But the results of these tests are often vague and difficult to interpret. If collectively they all point to the same conclusion, then fine. But when they don't a dentist will probably not perform endodontic treatment for fear that it is unneeded.

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