What is TMJ?
Dental students, hygiene students and assistants who want to know more about the technical aspects of occlusion should also see my companion page on occlusion and the internal arrangement of the TMJ.
The term “TMJ” is the acronym for “TemporoMandibular Joint”. This is the ball and socket joint that allows the lower jaw to open, close and move sideways when chewing and speaking. Everyone, of course, has two of them, and they are located about one centimeter in front of the ears. They are the only joints in the head, and if something goes wrong with either one of them, you can have serious problems.
You may have pain on opening or closing your mouth, eating and chewing food, and even speaking. Problems of this nature are what the public generally associate with the term “TMJ”.
In the panoramic x-ray above, the TemporoMandibular Joints (TMJ’S) are visible in the upper right and upper left corners of the film. The TMJ is typical of the type of joint called a “ball and socket”. The ball is the rounded eminence visible in the detail to the right and is technically known as the “condyle” of the joint. The ball rotates in a cuplike depression (the socket) technically known as the “fossa“. Although the joint looks like it is attached directly to the sinuses, it is actually separated from them by soft tissue ligaments which entirely enclose the joint, but are not visible on an x-ray. Also not visible is the meniscus which is a disk of cartilage which lives in the space between the condyle and the fossa and is capable of moving forward and backward as the jaw opens and closes. The condyle and the fossa are each covered with a thin layer of non movable cartilage of their own. All three layers of cartilage help to provide smooth, frictionless surfaces for comfortable joint operation.
When a dentist thinks of TMJ, he or she tends to think more globally than just the anatomy of the joint. The joint is really a part of the larger system that makes the jaws work. To a dentist, TMJ problems include not only the joints themselves, but also the muscles, tendons and ligaments that allow them to move, and in fact, it is usually pain in these structures that drives most patients toward TMJ treatment. In dentistry, there are several different terms used to describe the problems associated with the “syndrome” (defined as a group of symptoms which have a common origin). Each term generally corresponds to a particular “era” in the history of the study of the illness, but all are still in common use and mean much the same thing with emphasis on slightly different aspect of the syndrome. They include MPD (MyoFascial Pain dysfunction), MFPDS (MyoFascial Pain dysfunction Syndrome), the more general TMD (TemperoMandibular Dysfunction) and the latest in a long line, Craniomandibular Disorders (CMD).
For the purposes of this discussion, I will use the term TMD to distinguish the painful symptoms of the disease from “TMJ”, the name for the joint itself.
The symptoms of TMD include the following: Headaches, neck ache or stiff neck, earaches (actually pain in front of the ears), jaw aching, difficulty opening or staying open at the dentist’s office, on opening the mouth, inability to open the jaws wide, especially at the dentist’s office, and sometimes an inability to open the mouth at all, pain on chewing, sensitive teeth, phantom tooth pain, a tendency to dislocate the jaw, and clicking, popping or grinding noises when opening or closing the mouth. Finally, TMD sufferers are prone to many more than the average number of complications from routine dental treatment.
All of these symptoms can range in severity from mild to devastating. The most prominent case of TMD that I am aware of was that of the actor, Burt Reynolds. His pain derailed his career, brought about drug addiction, and was a factor in his several divorces. A great deal of his suffering was due to the fact that TMD was only beginning to be understood as a disease entity at that time. Even today, there is still a great deal of misunderstanding about the true causes of this syndrome, even among dentists, and thus you will find a great deal of disagreement about the correct treatment. This is slowly changing as dental schools are now teaching relevant courses in occlusion.
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