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PubMed1980

Accessory medial pterygoid muscle.

A previously undescribed accessory medial pterygoid muscle occurred uniformly in the dissection room population studied. The origin extends from the superior margin of the pterygoid plate and skirts medially of foramen spinosum and ovale, finally terminating on the carotid canal rim. The flat triangular muscle descends to insert its apex into the medial surface of the medial pterygoid muscle about 1 cm below its exit from the pterygoid fossae. Histologic examination confirmed striated muscle. Independent innervation arises from the medial surface of the mandibular nerve trunk just below the foramen ovale and enters the accessory medial pterygoid lateral surface at about the upper third, centrally. Muscle function is suggested as a discriminating action, rein-like in nature, probably corresponding to Bennett movement. Variation in size of this muscle may also explain the range observed for Bennett movement. The dental occlusal action field is suggested to be the buccal aspect of the last molar tooth.

Adipose Tissue↗
PubMed2004

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

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.

Bite Force↗
PubMed1997

Morphometric analysis of the insertion of the upper head of the lateral pterygoid muscle.

OBJECTIVE: This article reports on the morphometric characteristics of the upper head of the lateral pterygoid muscle. STUDY DESIGN: Several morphologic characteristics were initially examined in 40 postmortem specimens. The length of the upper head of the lateral pterygoid muscle was determined in 34 specimens. Of the 26 specimens in which the upper head of the lateral pterygoid muscle was found to be inserted into the meniscus and condyle, 22 specimens were examined microscopically to morphometrically quantify the proportion of muscle fibers to their respective insertions. RESULTS: The upper head of the lateral pterygoid muscle was approximately 33.3 mm in length and was significantly longer in males. There were no age-related differences. Approximately 29.5% of the fibers of this muscle were inserted into the meniscus of the temporomandibular joint. CONCLUSION: This study demonstrated that the insertion of the upper head of the lateral pterygoid muscle to the meniscus ranged from a fleshy mass to a few fibers. The number of fibers entering both the meniscus and the condyle decreased correspondingly as they approached the joint and could be interpreted as this muscle having a tendon of insertion into the meniscus.

Adult↗
PubMed2003

Spatial relationships between masticatory muscles and their innervating nerves in man with special reference to the medial pterygoid muscle and its accessory muscle bundle.

The relationships between the positional arrangement of the surrounding and innervating nerves of the muscles supplied by the mandibular nerve, in particular those medial to the main trunk of the nerve, were examined in 24 head halves from 12 Japanese cadavers by dissection from the inside after removal of the bony elements except for the mandible. In ten sides of five heads, the lingual nerve pierced the medial pterygoid muscle, and the bundle lateral to the nerve was found to be separated as an accessory muscle bundle. The accessory bundle was frequently attached to the mylohyoid muscle. In addition, the inferior alveolar nerve and the lingual nerve frequently communicated, and in four specimens a branch from the lingual nerve entered the mylohyoid to communicate with the proper nerve. The innervation pattern indicated that the medial pterygoid muscle consists of the anteromedial and the posterolateral main parts, and sometimes has an accessory bundle. Based on the present findings and the previous studies of the positional relationships between the muscles and nerves by our research group, we propose that the muscles innervated by the mandibular nerve could be classified as an inner group (the lateral pterygoid) and an outer group (the other muscles). A possible scheme of the positional relationships between the muscles and nerves is presented.

Aged↗
PubMed1995

A literature survey of a hundred years of anatomic and functional lateral pterygoid muscle research.

Controversial topics that influence the etiology and the treatment of temporomandibular disorders include anatomy and function of the lateral pterygoid muscle, and the nature of the disc-muscle connection. To explore whether an agreement has been reached among researchers, a literature survey focusing on the structure, performance, and disc-muscle interface of the lateral pterygoid muscle was performed. Eighty-nine original research articles were identified in the Index Medicus information system from 1879 to 1994 by applying the keyword phrase "lateral pterygoid muscle." A majority of references (65%) identified two separate parts of the lateral pterygoid muscle as well as insertions into the disc, the capsule, and the condyle. Seventy-five percent of the articles agreed on three major functions. This literature survey revealed a consensus regarding anatomy, function, and disc connection among the majority of the researchers. However, diverging opinions were persistent and could be identified.

Humans↗
PubMed1990

Nerve entrapment in the lateral pterygoid muscle.

The posterior trunk of the mandibular division of the trigeminal nerve normally descends deep to the lateral pterygoid muscle. In three of 52 dissections the three main branches of the posterior trunk (lingual, inferior alveolar, and auriculotemporal nerves) were observed to pass through the medial fibers of the lower belly of the lateral pterygoid muscle. The mylohyoid and anterior deep temporal nerves also were observed to pass through the lateral pterygoid muscle in other specimens. These nerve entrapments in the infratemporal fossa provide new information concerning the anatomic and clinical relationships between the mandibular nerve and the lateral pterygoid muscle. These findings support the hypothesis that a spastic condition of the lateral pterygoid muscle may be causally related to compression of an entrapped nerve that lead to numbness, pain, or both in the respective areas of nerve distribution.

Aged↗
PubMed1990

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

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.

Cephalometry↗
PubMed1993

The development of the temporomandibular joint: a review with regard to the lateral pterygoid muscle.

This review sets out to explore the relationship between the lateral pterygoid muscle and the meniscus. It examines the embryological evidence to explain the controversy surrounding the apparent morphological discrepancy in the attachment of the lateral pterygoid muscle to the meniscus. It shows that the contribution of the lateral pterygoid muscle to the formation of the meniscus remains in dispute. Morphogenetic studies have not been able to support either one or other viewpoint and no direct conclusions can therefore be made on the embryology of the temporomandibular joint.

Humans↗
PubMed1996

Lateral pterygoid muscle and its relationship to the meniscus of the temporomandibular joint.

OBJECTIVE: The theory of internal derangement of the temporomandibular joint involves the anterior displacement of the meniscus, which is thought to be the result of hyperactivity of the lateral pterygoid muscle. There is, however, a great deal of confusion with respect to the attachment of this muscle to the meniscus. This anatomic study reexamines the meniscal attachment of the lateral pterygoid muscle, in particular, the upper head of this muscle. STUDY DESIGN: The anatomic relationship between the lateral pterygoid muscle and the meniscus was examined in the postmortem specimens of 25 males and 15 females between the ages of 7 to 85 years. RESULTS: In 65% of specimens, the upper head of the lateral pterygoid muscle was attached to the medial aspect of the capsule, meniscus, and to the pterygoid fovea of the condyle. In 27.5% of specimens, the upper head was attached solely to the condyle; in the remaining 7.5% of cases, there were other types of attachments of the lateral pterygoid muscle to the meniscus. CONCLUSION: This study confirms that the lateral pterygoid muscle has a variable attachment to the meniscus. The role of this muscle in the displacement of the meniscus is still unknown and further research into temporomandibular disorders should involve the investigation of other structures in the craniomandibular complex.

Adolescent↗
PubMed2001

Measurement of the size and orientation of human masseter and medial pterygoid muscles.

To gain a better understanding of biting and chewing performance, the size and orientation of the masseter and medial pterygoid muscles in living humans were studied. Twenty-seven young males having complete dentition, class I dental occlusion and normal muscle and jaw function were examined using magnetic resonance images of the head between the zygomatic arch and hyoid bone. The sections were parallel to the palatal plane, and the thickness was 3 mm without a gap. A computer software program (Medical Dental Image, MDI) was developed to identify and calculate the area of each cross section of the muscle, and the volume of the muscle was then estimated. The axis of the muscle was determined by connecting the centroids of the sections in the lower and upper 1/3 of the whole muscle. The effective muscle cross section area was then calculated by resectioning the muscle perpendicularly to the muscle axis. It was found that the mean masseter muscle volume was around 31 cm3, and that the mean medial pterygoid muscle volume was 11 cm3. Their mean effective cross section areas were around 6.2 cm2 and 3.5 cm2, respectively. The axis of the masseter muscle was more perpendicular to the palatal plane and parallel to the sagittal plane than was the medial pterygoid muscle. The results suggest that the use of magnetic resonance images (MRI) is an effective noninvasive measurement technique for determining the size and orientation of masseter and medial pterygoid muscles. This technique can be employed in future studies on human bite force evaluation and masticatory function.

Adolescent↗
PubMed2001

[An immunohistochemical study of distribution of insulin in lateral pterygoid muscle after functional mandibular protrusion in rats].

OBJECTIVE: The aim of this study is to investigate the effects of insulin on the lateral pterygoid muscle of growing rats after the functional mandibular protrusion. METHODS: An immunohistochemical (the ABC method) method was used to detect the location and distribution of insulin in the lateral pterygoid muscle of rats. RESULTS: 1. Insulin located in the cell membrane of the lateral pterygoid muscle. 2. The distribution of insulin in the lateral pterygoid muscle of rats was enhanced after the functional mandibular protrusion. CONCLUSION: Insulin may play an important role in adaptive remodeling of the lateral pterygoid muscle after the treatment of functional mandibular protrusion.

Animals↗
PubMed1999

[A radioimmunologic assay of insulin in lateral pterygoid muscle after functional mandibular protrusion in rats].

OBJECTIVE: To investigate the effect of insulin on the lateral pterygoid muscle after functional mandibular protrusion in rats. METHODS: Radioimmunoassay was used to examine the level of insulin in lateral pterygoid muscle quantitatively after functional mandibular protrusion in young growing rats. RESULTS: The amount of insulin in lateral pterygoid muscle in young growing rats enhanced after functional mandibular protrusion. CONCLUSION: Insulin plays an important role in adaptive remodeling of lateral pterygoid muscle after functional mandibular protrusion.

Animals↗
PubMed1993

The embryologic development of the human lateral pterygoid muscle and its relationships with the temporomandibular joint disc and Meckel's cartilage.

The morphology of the developing lateral pterygoid muscle and its relationships with the temporomandibular joint disc and Meckel's cartilage were studied in 16 human embryos and fetuses ranging in age from 5 weeks to 14 weeks. All the temporomandibular joint structures and the lateral pterygoid muscle assumed their adult shapes by the 14th week of fetal life. At this stage, the lateral pterygoid muscle is a complex structure with several aponeuroses dividing the muscle into three main parts: superior, inferomedial, and inferoanterior. The superior part is attached to the disc superiorly and medially. The inferomedial part inserts into the anteromedial aspect of the condyle and disc. The inferoanterior portion is attached to the anterior aspect of the condyle. Anteriorly, the buccal nerve and associating blood vessels traverse the muscle in a mediolateral direction, dividing it into superior (small) and inferior (large) compartments. Posteriorly, the muscle remains intact with no separation. The lateral pterygoid muscle fibers show no direct attachment to Meckel's cartilage at any stage of development.

Cartilage↗
PubMed1997

The role of the lateral pterygoid muscles in TMJ disorders during static conditions.

Intramuscular EMG of the lateral pterygoid muscles (LPM), surface EMG of the temporalis and masseter muscles and force measurements of the temporomandibular joint (TMJ) were synchronously used to investigate the biomechanical role of the two heads of the LPM in relation to internal derangement (ID) of the TMJ. EMG and kinetic analysis of five static conditions (resting, protraction, opening, molar and incisor clenching) and three maximum isometric masticatory forces (opening, molar and incisor clenching) were done to compare forces and muscular activity between TMJ ID and control subjects. The analysis of variance results of the integrated linear envelope (LE) EMG showed no significant differences between the two groups for the masseter and temporalis muscles. Therefore, there is no apparent reason to believe that these muscles are hyperactive in TMJ ID. The integrated LE EMG of the SLP was significantly lower in the TMJ group during molar clenching (104 microV + 60.0 over 159 microV + 68.8 for a p = .020). The superior head of the lateral pterygoid muscle (SLP) seemed to have lost its diskal stabilizing function. The integrated LE EMG signals of the ILP were significantly higher in the TMJ ID group during rest, resisted protraction and incisor clenching (p = .029, p = .046, p = .031 respectively). The ILP muscle has probably adapted to control the inner joint instability while continuing its own actions. The ILP muscle seemed to have lost its functional specificity. The results of the isometric forces showed that TMJ ID subjects exhibited significantly lower molar bite forces (297.1N over 419N, p = .042) confirming that they have less muscle strength and tissue tolerance than subjects with healthy masticatory muscle systems. A neuromuscular adaptation could be occurring in the TMJ ID masticatory system affecting muscular actions and forces.

Adaptation, Physiological↗
PubMed2006

The human lateral pterygoid muscle.

One of the jaw muscles particularly implicated in temporomandibular disorders (TMD), a common form of non-dental chronic orofacial pain, is the human lateral pterygoid muscle. The precise role of this muscle in TMD is unclear as is the nature of the interaction between pain and motor function particularly involving this muscle. This research group has adopted a two-stage approach to studying the effects of pain on motor function. The first is to study normal orofacial motor function through recordings of jaw movement and electromyographic (EMG) activity from a number of jaw muscles (including recordings from the lateral pterygoid muscle; verification of electrode location achieved through computer tomography imaging) during a number of standardised jaw movements. These studies have defined the detailed functional properties of, in particular, the lateral pterygoid muscle, whose physiology and function is not well understood. In summary, the data are consistent with the hypothesis previously proposed that the lateral pterygoid should be regarded as a system of fibres that acts as one muscle, with varying amounts of evenly graded activity throughout its entire range, and with the distribution of activity within the muscle being determined by the biomechanical demands of the task. Our second approach has been to study the effects of experimental masseter muscle pain on the detailed functional properties (e.g., root-mean-square EMG activity) of the jaw muscles, especially the lateral pterygoid muscle. Preliminary data from these pain studies point towards significant effects of human experimental muscle pain on jaw muscle activity and jaw movement.

Electromyography↗
PubMed1995

Effects of lateral pterygoid muscle hyperactivity on differentiation of mandibular condyles in rats.

BACKGROUND: The effects of biomechanical stress on the growth and development of the mandibular condyle have been studied by many investigators. However, the role of the lateral pterygoid muscle in this development is not clear. METHODS: Hyperfunction of the lateral pterygoid muscles of male 3-week-old Sprague-Dawley rats was induced by electrical stimulation, and the responses of the mandibular condyles were compared to control tissues by a double-fluorescent staining technique using polyclonal antibodies against type I and type II collagen. Electrical stimulation consisted of repeated application (5 seconds on/5 seconds off) of a 5 Hz current for up to 7 days. RESULTS: In the first 2 days, cartilaginous tissues rich in type II collagen disappeared in the anterior and posterior areas, which were loaded by tensional force due to direct and indirect attachment of the lateral pterygoid muscles. Tissues in these areas were replaced by intramembranous bone that was reactive for type I collagen at 7 days. By the end of the experiment, the trabecula of the condyle was remodeled more perpendicularly, thus resisting the compressive force due to hyperfunction of the lateral pterygoid muscles. CONCLUSIONS: These results suggest that the activity of the lateral pterygoid muscle might play a significant role in the differentiation of progenitor cells and in the maturation and calcification of chondrocytes in mandibular condyles.

Animals↗
PubMed1990

Myotomy of the lateral pterygoid muscle and condylar cartilage growth.

The influence of lateral pterygoid muscle activity on growth of the condylar cartilage of the mandible remains controversial. As a case in point, two recent studies involving total resection (myectomy) and sectioning (myotomy) of this muscle have come to contradictory conclusions. In the study reported here, it was found that young growing rats in which the lateral pterygoid muscle was bilaterally cut experienced significantly retarded mitotic activity and bone formation relative to their sham-operated counterparts. Changes in the shape and topographical distribution of cartilage over the condylar head, as well as the distribution of labelled cells, were also noted in myotomy animals at 4 days following surgery. Considerable resorption at the insertion of the muscle on the mandibular ramus was apparent at 14 days after surgery. However, the myotomy surgery was accompanied by a significant post-operative loss of body weight and incisal supra-eruption indicative of feeding difficulties, thereby complicating interpretation of the results.

Animals↗