Orientation and Function of the Lateral Pterygoid

The purpose of the lateral pterygoids is to work together to pull the mandible forward
("advance" it), and to translate the condyles (open the mouth).
(Although one lateral pterygoid can contract without the other, the result is
a swinging of the mandible to the opposite side, and serves no functional purpose.)

(The image-link above take's you to a Flash Animation of the condyles translating.
The lateral pterygoids are not shown, but their effect is)

The contraction of only one of the lateral pterygoids (when the teeth are apart)
will swing the mandible to the opposite side, and is a purposeless act.
Once the jaw has been elevated (by the temporalis, green arrows)
and there is a tooth contact (target), contraction of the lateral pterygoid(s)
is parafunctional.  During function (chewing), there is no purpose in the attempt to
translate the condyle. The intensity of the parafunctional contractions will dictate
the degree of resultant signs and/or symptoms, if any.

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