I had a root canal 5 years ago and a crown put on top, on the bottom right part of my mouth. It fit well and I experienced no pain. A month ago I went to the dentist for a bonding on the upper right side of my mouth and suddenly my crown began to hurt. It is very painful to chew, and it is very sensitive to cold. I don't know what it could be and I am afraid to ask the dentist. Can anyone help me and tell me what it could be?

Why would you ask us and not your dentist? That seems a bit silly doesn't it? My best friend is a dentist and always tell me teeth have one type of nerve, a pain nerve. The tooth is totally dead at this point so the pain you feel is likely just below the tooth. You may have developed an abscess. In any case tell you dentist since it is likely you'll need a script.