TMJ Function
Illustrations courtesy of Brendan Stack
Normal TMJ Function
When
the mouth opens, two distinct motions occur in 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.
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.
 .
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 receding 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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