loss of cortical plate or flattening of the superior surface of the condyle

even with a modern panoramic, the relative position of the condyle in the glenoid fossa cannot be determined. You cannot see boney changes such as loss of cortical plate or flattening of the superior surface of the condyle on a panoramic x-ray. The reason for this stems from the angulation of the x-ray beam through the condyle itself. Because the x-ray beam is directed from a position under the joint, the lateral pole of the condyle is projected upward and therefore details are lost because the image is superimposed over other boney structures. A panoramic may provide lots of information about other things, but don’t depend on a panoramic to tell you much of anything about the joint.

http://halligantmj.com/quick-and-easy-tmj-xray-basics/