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Normal Unilateral Activity and Effect of a Lateral Pterygoid Muscle |
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| Although Lateral Pterygoids are intended to work together to depress the mandible, a voluntary unilateral activity results in an excursive movement to the contralateral side.
In the example to the right, the contraction of the left inferior belly of the LP advances/translates its condyle and then pulls it still further medially. Following the cessation of its contraction, the reciprocal activity of the temporalis' then elevate the mandible (the superior belly of the LP contracts simultaneously with the temporalis, thought to thereby stabilize the disc assembly).
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Practitioners may be familiar with the effect of a unilateral LP contraction following a PSA anesthetic block. The ipsilateral LP may be anesthetized and not able to advance its condyle. The opposite side LP pulls its condyle anterio-medially, while the anesthetized side opens very little, as demonstrated in the graphic above right.
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An imbalance of opening efforts can be seen in the garage door
example above. The absence of the left spring prevents the
door from opening fully on the left side. In the jaw example above, absence of right LP contraction results in a left excursive
movement.
Deviations upon opening are most likely due to differences in tension of the two lateral pterygoids.
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