I can understand why you are confused. So let’s break it down.
It is important to know why the tooth is having a crown placed, and the condition of the tooth before the crown is placed. You can also go to the Services and Care section of our website, and read about crowns and root canal treatments.
We place crowns for multiple reasons. The major reasons are:
1. a large previous filling that has broken down or has new decay, and needs to be replaced, but there will not be enough tooth remaining to support the stresses and forces of chewing.
2. A broken cusp or a vertical fracture in the tooth, when the exam and your symptoms show that a filling just won’t be enough.
3. A back tooth after having had a root canal treatment, or a front tooth after a root canal treatment where there is existing damage to the tooth structure, or a large previous filling.
There are some other reasons, but for sake of this discussion, those are the big ones.
We do a root canal treatment when the living part of the inside of a tooth is irreversibly damaged, and your symptoms confirm the need. Many teeth that need crowns do not have symptoms that indicate or confirm the need for a root canal treatment. This is not to say it might not in the future, but at the time of treatment the root canal therapy is not indicated.
An adult can put tremendous pressure on their back teeth when chewing, clenching, or grinding. I have read research articles that say we can put as much as 250-300 pounds per square inch on our back teeth! And when we are asleep, that amount can increase 6-10 fold!
We have always known that placing a crown on a back tooth with a root canal treatment is indicated to protect the tooth from those big-time forces. But now we have studies that show that the more important reason to place a crown is to provide total coverage and seal over the tooth to prevent what is called micro-leakage. This is the infiltration of saliva, acids, and bacteria that take place over time around a filling. If these bacteria get to the root canal seal, then the seal may fail. This may result in a root canal therapy re-treatment, or possibly (infrequently) loss of the tooth.
So, in answer to your question: Almost every tooth that has had a root canal treatment will need a crown, but not every tooth that has a crown will need a root canal treatment. Each tooth will be evaluated individually, and the treatment planned, determined, and discussed with you.
Still confused? Ask Dr. Bob at your next visit.