Jaw Joint (TMJ) X-ray (both sides, open and closed)

What it is

The temporomandibular joint sits just in front of each ear, where the lower jaw meets the skull. It both hinges and slides, so the head of the jawbone travels forward as the mouth opens. This study takes radiographs of both joints in two states — mouth closed and mouth open — so the bony surfaces can be assessed and, more usefully, so the excursion of each side can be compared against the other. Both sides are imaged because a joint that moves oddly is often only recognizable next to its pair. Plain films show bone; the disc inside the joint, the muscles, and the ligaments are soft tissue and do not appear, which is why MRI is used when those are the question.

Why it is done

• To assess jaw pain, stiffness, or limited opening, when a bony cause is being considered
• To compare how far each joint translates forward on opening, in someone whose jaw deviates to one side or locks
• To look for changes in the joint surfaces in arthritis, or for damage after an injury to the jaw

What to expect

Nothing to prepare, and nothing to remove except earrings, glasses, and anything else metal around the head. You sit or lie with your head held in position while the technologist takes films of one side, then the other, first with your teeth together and then with your mouth open as wide as it comfortably goes. Holding the open position for a few seconds is the only awkward part, and it can be uncomfortable if opening is what hurts — say so, because the study is about what you can actually do, not what you can force. It takes a few minutes. The NIDCR notes that there is no single test that diagnoses these disorders; imaging is read alongside the history and a hands-on examination, and clicking without pain generally needs no treatment at all.

Questions worth asking

• Is this being billed through medical insurance or dental? TMJ imaging falls between the two, and some plans exclude jaw joint care entirely.
• Bilateral is built into this study — confirm you are not being charged twice, once per side.
• If a panoramic dental x-ray or a cone-beam CT is recommended instead or in addition, how do those prices compare?
• Was this taken in a dental office, an oral surgeon's office, or a hospital radiology department, and is the interpretation included?