Are the two heads of the human lateral pterygoid separate muscles? A perspective based on their nerve supply.

Based on biomechanic and electromyographic studies, it has been argued that the two heads of the human lateral pterygoid muscle (LPt) are reciprocally active during the masticatory cycle. Thus, it has been proposed that the heads be considered separate muscles. However, questions about the accuracy of these data have arisen. The authors hypothesized that partition cannot be complete without an independent nerve supply. To test this, complete unilateral lateral pterygoidectomies were performed on 20 dissection room cadavers. A novel approach, using an en bloc method, proved optimal to expose the detailed nerve supply to the LPt heads. In the two most frequently observed patterns (15 of the 20 specimens), the heads were supplied from a common source that was derived from either the long buccal or mandibular nerve, or from a loop that arose between the long buccal and lingual nerves. In a third pattern, independent branches to either head arose from the deep temporal, long buccal, or mandibular nerve. In only 20% of the specimens did the two heads receive exclusive innervation from separate sources. The most significant finding of the present study is that both LPt heads in humans are usually supplied by a common proximate source, but each head also receives independent nerves in every case. In the absence of precise information about the functional components in each nerve branch, these data appear to support Juniper's proposal to regard the two LPt heads as entirely separate muscles.