Generally, a tooth should have a crown placed after a root canal is done. This is because the tooth needed a root canal in the first place because of a large cavity and there is not enough tooth to hold a filling. In addition, after a root canal, the tooth becomes very brittle and is inclined to break. Sometimes a small piece breaks off and a crown can still be done. Sometimes a large piece breaks off below the gum or the tooth cracks below the gum and the tooth has to be extracted.
If you had a filling placed in the tooth after the root canal and the tooth still hurts, you should:
--Get a second opinion from another dentist, preferably a specialist in root canals, an endodontist. He or she will take another x-ray and tell you if the root canal has indeed healed well.
--Find out if the tooth is cracked. You can test this yourself by biting down on a popsicle stick or wooden chop stick placed on only the painful tooth. If the tooth gives a sharp, quick stab of pain that goes away when you stop biting, it is probably cracked. If the crack stops above the gum, a crown may help. If the crack goes below the gum, the tooth has to be extracted. It is difficult for any dentist to tell how deep a crack goes. Some specialists have a small camera that can go between the gum and the tooth to follow the crack and see where it stops. Obviously, this is an expensive procedure.
If the dentist who did the root canal is not a specialist (endodontist), I would definetely seek a second opinion as to the quality and healing of the existing root canal. If the root canal missed part of the nerve or the root canal filling goes beyond the root, the root canal may be a candidate for a redo. This costs about $1000. A crown will cost about $800. An extraction will cost between $60 and $200, depending on the condition of the tooth. After an extraction, the tooth must be replaced, which will run into thousands of dollars. The sooner you get it taken care of, the greater chance that you can save the tooth.
I hope this helps you. If you have further questions after you see a dentist, contact me again.