What causes jaw to lock up?

Disk problem: As your jaw opens the bone slides along with the disk in the socket. If end of the bone and disk are out of sync then it can cause your jaw to get stuck or "lock" into an open position. If that happens try messaging the TMJ muscles to relax back to close. If your jaw locking problem becomes painful consult your dentist immediately.

Displaced disk: Your jaw may be locked, which means that the articular disk that joins the upper and lower jaws (maxilla and mandible, ) may be out of place. It may be displaced forward and does not allow the mandible to get back to its comfortable position and the lower teeth therefore do not come together.