It seems I have an abcess under my back molar and will need a root canal procedure. I also have a couple of cavities on the same tooth. I have the option of having a crown made to cover the hole for the root canal as well as take care of the fillings--or I can simply have the hole plugged and the cavities filled. The crown costs more but should be a longer-lasting solution. I'm not sure what to do. Suggestions?