Could my molars be cracked under the crown?

Hi:I have seen many patients that do bruxism crack back molar teeth even under the crown.  Best,Dr. Maddahi

It is not uncommon for a root canaled tooth to crack under a crown unfortunately. You would need xray confirmation.

After having a root canal, a tooth can become brittle and crack. It is not uncommon to have a root crack on a root canaled tooth years after root canal treatment. It would only be visible on a 3D scan. It won’t show up on an X-ray. 

Thank you for your question.  Although there are many reasons your tooth can be sensitive, it's definitely possible that you have a root fracture on that tooth.  The best thing to do would be to have the area checked out by an endodontist.  This way, a series of testing can be done to confirm a diagnosis and your treatment options can be given to you! I would see an endodontist sooner than later!