Normal cross-section of a human temporomandibular joint (TMJ)
Disorders of the Temporomandibular Joint (TMJ) occur in about 25% of the U.S. population. Most people having TMJ problems are not seriously enough affected to have discomfort. However, a certain portion of Temporomandibular Disorder (TMD) suffers have pain severe enough to seek treartment. Until recently, disorders of this kind were poorly understood and were just grouped together in a catch-all diagnosis of TMJ Syndrome or just "TMJ". We now know there are over 50 separate disorders that can affect the TMJ and its associated structures. With this realization, real progress has been made in the diagnosis and treatment of these problems
There are two main categories of TMD. The first are true joint disorders known as "Intracapsular Disorders". These problems occur within the confines of the joint itself and affect the bones, cartilage and ligaments of the joint. The second categoriy is the "Neuromuscular Disorders". These are problems with the supporting nerves, muscles, blood vessels and accessory ligaments in the face and neck surrounding the joint.
The most common of the disorders of these categories will be discussed here. There is also another good TMJ tutorial on the Web that can be accessed by clicking here.
The most common of all intracapsular disorders is a displacement of the articular "disc" (see above picture). Normally this structure remains between the condyle (the bony end of the lower jaw ) and the glenoid fossa (the socket in the base of the skull that houses the TMJ) at all times.
Occasionally the cartilage will become displaced (usually in a forward direction) and when the patient opens the cartilage pops back into the proper position causing a clicking sound. Upon closing the cartilage slips out of position usually without causing any noise.
Displaced disc. (14k jpeg) In this cross section of a TMJ, the disc has slipped forward and is no longer positioned between the condyle and the fossa. Compare this image to the normal joint seen at the top of this page. Upon opening the condyle moves down and forward (red arrow) and the disc pops back into place. (Next image) Note how the disc is slightly folded.
Displaced disc reduced into proper position upon opening (arrow). (14k jpeg) Same joint as above after opening. The disc has popped into the proper location . Upon closing the disc slips out from between the condyle and fossa and remains anteriorly displaced. This condition is the most common (although not the only) reason for joint clicking.
Abnormal TMJ. Magnetic resonance image of a displaced disc. (22K jpeg)
Magnetic resonance imaging of the TM joint is the best way to visualize disc problems. In this image of the joint the disc is displaced in front of the condyle. In some instances a plastic appliance called a "splint" or "bite plane" can be made to allow the disc to return to the proper position.
Lower splint. (22K jpeg)
This type of appliance is designed to reposition the lower jaw in so that the disc will be maintained in the proper position.
Close-up of lower splint smile. (22K jpeg)
These appliances are relatively inobtrusive and the patients usually adapt quickly to wearing them.
Lower splint smile. (22K jpeg)
Abnormal TMJ. The disc is chronically displaced in front of the condyle and is mis-shapen. (22K jpeg)
Sometimes the cartilage will become displaced and will not pop back into position when the patient opens. When this happens the disc often becomes an obstruction to the full range of motion of the condyle and the patient experiences a limitation of opening. This can occur quite suddenly and is sometimes painfull as well. When this occurs the patient should not try to force the jaw open as this could cause more damage to the structures. Immediate professional care should be sought to determine whether the disc can be manipulated back to the proper location.
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