Why is placing a dental crown on a tooth that has had root canal treatment often the best choice?
A dentist will often recommend to a patient that once their tooth's root canal treatment has been completed the type of restoration that is placed should be a dental crown placed, as opposed to a filling. This is especially likely if the tooth being treated is a posterior tooth, such as a molar.
Why is a crown often a better choice than a dental filling for a tooth that has had root canal treatment?
The reasoning associated with this determination is typically founded upon the fact that teeth that have had endondontic treatment are often in a state where structurally they have become compromised, possibly significantly so. This is because, typically, those teeth that require root canal treatment are those who have already experience some type of traumatic event (such as a large cavity or else breakage). Add to this the fact that in order to perform their root canal work, the treating dentist or endodontist has created an access cavity through the chewing aspect of the tooth extending to tooth's pulp chamber. These two events in combination typically involve the loss of enough tooth structure that the tooth is structurally weakened. If this is the case, the protection of a dental crown is indicated.
[ More about why a "root canalled" tooth might need the protections of a dental crown. >> ]
Another reason why the treating dentist might make the recommendation that a crown should be placed instead of a dental filling is has to do with the fact that a crown creates the best possible seal for a tooth. If contaminates from the oral environment are allowed to seep back into the confines of an endodontically treated tooth (a process termed "coronal leakage") the success of the root canal treatment will be compromised. A dental crown, more than any other type of restoration, can help to predictably prevent this.
[ More about coronal leakage and how it can lead to root canal treatment failure. >> ]
Dental research supports the opinion about the need for a dental crown for endodontically treated teeth.
Several studies have evaluated the outcomes associated with teeth that have had root canal treatment and then were, or were not, crowned. Here are the findings of some of them.
Aquilino (2002) - This study evaluated the experiences of 400 endodontically treated teeth and found that those that were not crowned after the completion of their root canal treatment were lost at a rate 6 times greater than teeth that had dental crowns placed.
Nagasiri (2004) - This study evaluated 220 molars that did not receive dental crowns after root canal treatment. The survival rates of these teeth at 1, 2 and 5 years were 96%, 88% and 36% respectively. However, the 5-year survival rate of molars that still had an "optimal" amount of tooth structure remaining after their endodontic treatment was 78%.
Lynch (2004) - This study evaluated 176 endontically teeth for a three year period following the completion of their treatment. The following survival rates were observed for teeth with the following types of restorations: cast restoration (dental crown) - 92%, amalgam restorations ("silver" filling) - 67%, composite restorations (tooth bonding) - 35%.
This is not to say that the placement of a dental crown after root canal treatment is always needed or that doing so will unequivocally mean that you will never experience a problem with the tooth again. What it does mean, however, is that if your dentist feels that a dental crown is indicated that following their advice is a smart thing to do if the long-term retention of the tooth is one of your primary goals (which it should be).
