TMJ Rotation and Translation

A series of views of the temporomandibular joint in different jaw positions within Posselt's envelope of motion, from teeth together in retruded contact through to wide opening, with a skull profile for orientation.

In the first 20 to 25 mm of opening the condyle mainly rotates in the lower joint compartment. Beyond that, it translates forward with the disc onto the articular eminence, which is how the mouth opens fully. Exams use this to ask about normal opening range, the terminal hinge axis used in prosthodontics, and why limited opening with deviation to one side suggests a problem on that side. Posselt's envelope itself is a common prosthodontics and occlusion recall item.