How the TMJ Functions

Normal TMJ Function

When the mouth opens, two distinct motions occur at the joint.   The first motion is ROTATION around a horizontal axis through the condylar heads.   The second motion is TRANSLATION.  The condyle and meniscus move together anteriorly beneath the articular eminence.  In the closed mouth position, the thick posterior band of the meniscus lies immediately above the condyle.  As the condyle translates forward, the thinner intermediate zone of the meniscus becomes the articulating surface between the condyle and the articular eminence.  When the mouth is fully open, the condyle may lie beneath the anterior band of the meniscus.

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Abnormal TMJ Function

Anterior Displacement With Reduction

INTERNAL DERANGEMENT of the TMJ is present when the posterior band of the meniscus is anteriorly displaced in front of the condyle.  As the meniscus translates anteriorly, the posterior band remains in front of the condyle and the bilaminar zone becomes abnormally stretched and attenuated.  Often the displaced posterior band will return to its normal position when the condyle reaches a certain point.  This derangement causes you to hear a "popping" or "clicking" sound in your ear.

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Anterior Displacement Without Reduction

In some patients the meniscus remains anteriorly displaced at full opening.   Patients with anterior displacement without reduction often cannot fully open their mouths.  Sometimes there is a tear or perforation of the meniscus.  Grinding noises in the joint are often present.  This is a much more severe condition than the "Popping" TMJ.  It leads to osteoarthritis of the jaw joint.  The joint breaks down and results in a receeding chin and protruding teeth as time goes by.   If the displaced disc is pressing against the inner ear, you will probably get subjective hearing loss and other ear symptoms.

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