Needing a crown does not necessarily mean you need a root canal, and in fact a minority of teeth that need a crown will need a root canal. Teeth need crowns when cracked or when they have a large cavity or filling. When we have a tooth like this, there is always a possibility of needing a root canal due to infection or nerve damage inside the tooth. However, we will not recommend a root canal unless a tooth truly requires one.
Some teeth will require root canals after the crown has been prepped and completed. This can be due to a nerve that was already damaged, a crack going deeper than expected, bacteria penetrating deeper into the tooth, or other unknown causes.