Organic TM Joint dysfunction
The temporomandibular joints are “Ball and socket” joints. Ball and socket-type joints are built like the joints in your shoulders and pelvis with a ball-like structure on the end of one bone that rotates within a socket-like hollow in an adjoining bone. The ball and socket of the bones are always separated by several layers of soft, slippery cartilage. Both the ball and the socket are coated with thin layers of cartilage, and there is always a movable layer of cartilage between them called a meniscus. The TM joint is built like the diagram below:
The ball portion of the lower jaw (mandible) is called the condyle. The socket is called the glenoid fossa and is in a part of the skull called the zygomatic arch. The anterior part of the glenoid fossa is a hump of bone called the articular eminence. Between the condyle and the socket is a movable layer of cartilage called the articular disc, (or the meniscus–See the diagram above. When a person opens his or her jaw, the first motion is simply a rotation of the disc in the socket. However when that person opens the jaw wider, the condyle slips forward toward the articular eminence. this movement is called “translation” of the condyle, and during translation, the articular disc moves forward along with the condyle so that it always remains between the condyle and the socket. It does this because its movements are coordinated by an attachment to the lateral pterygoid, a little muscle in front of the ear whose main job is to draw the lower jaw forward.
If someone clenches or grinds their teeth (bruxing), or if a person suffers a traumatic incident to the jaw, the meniscus may suffer an injury. It may tear, or perforate (a hole created by the prolonged pressure). If that happens, the joint may be drawn forward, in front of the condyle causing a loud snap when the condyle suddenly snaps against the socket bone.
This can happen in reverse upon closing as well. Most of the time, these noises are NOT accompanied by pain, and it has become the common practice in dentistry NOT to treat these patients if the popping noises are the only symptom of the disease. For a much more detailed discussion of this subject, please see to my 7 page essay on occlusion.
In other patients these organic changes can produce joint inflammation (arthritis) which can be quite painful and lead to other degenerative changes in the joint. Sometimes, the bones are forced into such close approximation that you might hear a grinding noise (crepitus) when opening or closing. Crepitus can be an indication of more advanced deterioration, and it may be time to seek the advice of an oral surgeon. (Note: Cartilage lines both the condyle (the ball) and the articular fossa (the socket) within the joint. The meniscus (disk) is a third layer of cartilage that is sandwiched between the other two layers. If you can hear actual crepitus, it generally means that all three layers of cartilage have been damaged, or are actually missing, allowing the unprotected bone of the ball to grind into the unprotected bone of the socket.) Whenever there is a suspected organic joint dysfunction linked to severe localized pain in the joint, special medical tests are needed to assess the extent of the damage, and the situation has progressed into the hands of specialists. Fortunately, this situation is very rare.