HiCustomer Thank you for asking your question on JustAnswer. Teeth have a covering called enamel, and beneath that a layer of dentin. Under this, and at the center of the tooth is the area containing pulp and nerves traveling down a canal to the bone beneath. Various factors cause the areas of the tooth to decay causing small holes or cavities. As the decay deepens through the enamel and dentin, the underlying pulp and surrounding gums can become infected and inflamed affecting the nerve and causing pain. Fillings are the first defense, intended to stop decay before it progresses. Once it is into the underlying pulp the area swells, there is pain and blood flow to the pulp is disrupted. Outside the actual pulp a pus sac can form, filled with dead tissue and bacteria, called an abscess. Even when antibiotics resolve the worst of the infection the inflammation and decay continues to affect the pulp and surrounding tissue the same way, and infection/abscess tend to recur. Pulling the tooth alleviates the issue by removing the chronically inflamed/infected tooth all together. To save the tooth a root canal removes the pulp, dead tissue and surrounding decayed tooth. A crown, made of porcelain or other material, is permanently glued in place. Root canal is usually recommended when decay is impinging chronically on the root and causes an abscess, and/or chronic pain and swelling.
Decay alone may or may not be easily visible to the naked eye, which is why regular check ups are recommended to spot areas of decay before they become cavities or progress further. The dentist will make the final recomendation regarding the need for a root canal but advanced decay, over large areas of the tooth that causes swelling, pain, or other problems are all signs that a root canal or extraction is necessary.
Sensitivity can persist after root canal, for up to six weeks. Past that stage it is possible that the root canal failed. Anomalies in the number or placement of canals, errors during the procedure, or incomplete cleaning of the canal can all lead to ongoing issues like you describe. Most dentisis should be willing to revise a root canal if symptoms persist, though yours sounds less accomadating than most. You can contact your Insurance Company directly, and explain the situation, but it is not likely they will pay for the revision if it is not specifically covered in your policy. A second opinion is your first step, however. Some dentists will offer an initial exam with x-rays free. A second opinion will at least give you an idea of what you are up against.