Most x-rays will not provide excellent clarity of a crowned tooth, thus missing the decay. If you are having pain, the tooth
under the crown
is inflamed, infected and bacteria are usually the cause. Antibiotics may provide some temporary partial relief but will likely not cure the problem. A root canal is most likely needed, and a dentist can do this, but the best is to see an Endodontics, which is a specialist for doing root canals.