Crown over cracked tooth?

My dentist put a crown on a tooth that is cracked. He said the crown would hold the tooth together and protect the tooth from cracking more. It has been a month and I still have a dull pain in the bone under that crown. I am also concerned that maybe the broken tooth is cracking more? but my dentist said that I would be calling him if it were because it would be REALLY painful. I am wondering why there is still a dull pain? he did tell me it would take a couple of months to heal but I am still concerned.

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