Monday, January 3, 2011

The human lateral pterygoid muscle: a review of some experimental aspects and possible clinical relevance

Aust Dent J. 2004 Mar;49(1):2-8.
Jaw Function and Orofacial Pain Research Unit, Faculty of Dentistry, The University of Sydney. gregm@usyd.edu.au


The clinical notion that some disturbance to the activity of the lateral pterygoid muscle plays a role in the aetiology of temporomandibular disorders (TMD) is still widely accepted and influences management strategies. However, there is no rigorous scientific evidence to support this clinical notion and the role of the lateral pterygoid muscle in normal function is still controversial. The classically defined functions of each head of the muscle are that the superior head is active on closing, retrusion, and ipsilateral jaw movements, while the inferior head is active on opening, protrusion and contralateral jaw movements. However, recent data indicate that these concepts are too simplistic. For example, recent evidence suggests that parts of the superior head may also be active on opening, protrusion and contralateral jaw movements, and that the superior head may consist of three mediolaterally arranged functional zones. Given these complexities, the proposal that clicking and/or locking conditions arise in the temporomandibular joint through some form of lack of co-ordination between the two heads of the muscle needs re-evaluation. Despite earlier reports to the contrary, both heads of the lateral pterygoid muscle appear to be electrically silent at the postural or resting jaw position, and therefore appear to play no role in the anteroposterior positioning of the jaw at the postural position. An important role has also been demonstrated electromyographically for progressive changes in activity in the inferior head as the direction of horizontal jaw force shifts from one side to the other. This suggests an important role for the lateral pterygoid muscle in the generation of side-to-side and protrusive jaw forces. The lateral pterygoid muscle is likely therefore to play an important role in parafunctional excursive jaw movements and also possibly a role in influencing jaw position in patients where the maxillomandibular relationship records change from session to session. The above data provide new insights into the normal function of the lateral pterygoid muscle. The proposal that the lateral pterygoid muscle plays some role in the aetiology of TMD needs now to be rigorously tested.
PMID: 15104127 [PubMed - indexed for MEDLINE]

A standardized technique for the placement of electrodes in the two heads of the lateral pterygoid muscle.

Koole P, Beenhakker F, de Jongh HJ, Boering G.:Cranio. 1990 Apr;8(2):154-62.

The results of electromyographic research on the two heads of the lateral pterygoid muscle depend largely on correct placement of the electrodes. Measurements were carried out on 24 male and 27 female skulls of known age and sex to determine the direction and depth of penetration for the placement of wire electrodes in the two heads of the lateral pterygoid muscle separately. The method of placement was simulated on human dissecting room material. With the use of a modified dental facebow, endodontic needles were placed in the direction of the two heads of the lateral pterygoid muscle in 11 human cadavers. The point of penetration was the most cranial point of the lower border of the zygomatic arch, lateral to the sigmoid notch of the mandible; after dissection over 80% of the needles proved to be placed correctly. The technique has since been used over 60 times on both heads of the lateral pterygoid muscle in volunteering dental students, dentists, and patients with symptoms of craniomandibular dysfunction. The technique interferes with the maximal opening of the mouth, which was reduced by about 10 mm. Subjects suffered slight inconveniences after the removal of the electrodes at the end of the test procedures. These inconveniences consisted of stiffness in the jaws and muscle soreness. Hematomas or infections did not occur.
PMID: 2073695 [PubMed - indexed for MEDLINE]

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