Fact-checked by Grok 2 weeks ago

Muscles of mastication

The muscles of mastication are a group of four primary skeletal muscles—the masseter, temporalis, medial pterygoid, and lateral pterygoid—that enable the elevation, depression, protrusion, retraction, and lateral excursion of the mandible to facilitate chewing and food processing.^[1] These muscles work in coordinated pairs to produce the complex mandibular movements essential for mastication, with the masseter and temporalis primarily responsible for forceful elevation and closure of the jaw, while the pterygoid muscles contribute to opening, protrusion, and side-to-side grinding actions.^[2] All four muscles originate from bony structures of the skull, such as the zygomatic arch, temporal fossa, and pterygoid plates, and insert onto the mandible, allowing precise control over jaw positioning during the masticatory cycle.^[1] Innervated exclusively by the mandibular branch of the trigeminal nerve (cranial nerve V3), these muscles receive motor supply through specific branches like the masseteric, deep temporal, and pterygoid nerves, ensuring synchronized activation for efficient chewing.^[2] Their blood supply derives primarily from branches of the maxillary artery, a terminal division of the external carotid artery, which supports their high metabolic demands during repetitive contractions.^[1] Embryologically, the muscles of mastication develop from the mesoderm of the first pharyngeal arch around the seventh week of gestation, with innervation established by the eighth week, reflecting their evolutionary role in feeding adaptations.^[1] Clinically, dysfunction in these muscles can lead to conditions such as myofascial pain syndrome, trismus, or temporomandibular joint disorders, often triggered by factors like bruxism, trauma, or malocclusion, highlighting their integral role in oral health and function.^[1]

Anatomy

Overview

The muscles of mastication are the primary muscles responsible for chewing and mandibular movements, comprising four main pairs: the masseter, temporalis, medial pterygoid, and lateral pterygoid.^[1] These muscles attach between the mandible and the cranium, forming a muscular sling that encircles and supports the lower jaw for efficient force transmission during mastication.^[3] The temporomandibular joint (TMJ) serves as the synovial joint enabling mandibular mobility, connecting the mandibular condyle to the temporal bone's mandibular fossa and articular tubercle.^[4] It features a fibrocartilaginous articular disc that divides the joint cavity into superior and inferior compartments, allowing for both hinge-like rotation and gliding motions, while ligaments such as the temporomandibular ligament, sphenomandibular ligament, and stylomandibular ligament provide stability and limit excessive movement.^[4] Auxiliary muscles, including the digastric and geniohyoid, assist in complementary actions like jaw depression by elevating the hyoid bone via a muscular sling, facilitating downward movement of the mandible.^[1] In evolutionary terms, these muscles adapted in mammals around 260 million years ago to facilitate precise occlusion and lateral jaw movements for food processing, with humans exhibiting reduced muscle size compared to herbivores due to shifts toward softer, cooked diets requiring less prolonged chewing.^[5]

Masseter muscle

The masseter muscle is a thick, quadrilateral muscle divided into superficial and deep heads, making it the most superficial and powerful elevator of the mandible among the muscles of mastication. The superficial head originates from the zygomatic process of the maxilla and the anterior two-thirds of the zygomatic arch, while the deep head originates from the medial surface of the zygomatic arch.^[6] Its fibers are arranged in a pennate fashion, with superficial fibers running posteriorly and inferiorly, and deep fibers running more vertically, contributing to its robust structure for forceful contractions. The muscle is composed of a heterogeneous mixture of type I slow-twitch and type II fast-twitch fibers, with regional variations.^[7] The superficial head inserts along the lateral surface of the ramus of the mandible, extending to the angle, whereas the deep head inserts into the upper half of the ramus and the coronoid process.^[6] This attachment pattern allows the masseter to exert significant leverage on the mandible during elevation. The muscle covers the lateral surface of the mandibular ramus and lies superficial to the lateral pterygoid muscle; it is pierced by the parotid duct as the duct courses anteriorly toward the buccinator muscle.^[8] With an approximate physiological cross-sectional area of 4-6 cm², the masseter is capable of generating approximately 100-250 N of force during clenching, underscoring its role in high-load masticatory tasks.^[9]^[10] It receives innervation via the masseteric nerve, a branch of the mandibular division of the trigeminal nerve (detailed in the Innervation section).

Temporalis muscle

The temporalis muscle is a broad, fan-shaped muscle that occupies the temporal fossa on the lateral aspect of the skull, serving as one of the primary elevators of the mandible during mastication.^[1] It features a complex arrangement of fibers that enable both vertical elevation and horizontal retraction of the jaw, contributing to chewing efficiency.^[1] The muscle's superficial position and tendon-mediated insertion distinguish it from other masticatory muscles like the masseter, which has a more direct extracranial attachment. The temporalis muscle originates as a fan-shaped sheet from the floor of the temporal fossa, extending from the inferior temporal line superiorly to the infratemporal crest inferiorly, and includes attachments to the deep surface of the temporal fascia covering the lateral skull surface.^[1] These origins span the temporal, frontal, and parietal bones, providing an extensive base for force generation. Its fibers converge inferiorly to form a thick, flattened tendon that inserts primarily on the medial surface, apex, and anterior border of the coronoid process of the mandible, with additional attachments along the anterior border of the mandibular ramus.^[1] The tendon passes medial to the coronoid process after traversing deep to the zygomatic arch, allowing efficient transmission of contractile forces to the mandible. Structurally, the temporalis is a large, radiating muscle divided into distinct fiber groups: anterior fibers run vertically for mandibular elevation, intermediate fibers course obliquely, and posterior fibers extend horizontally to facilitate retraction.^[1] It is rich in type I slow-twitch fibers, particularly in the intermediate (57%) and anterior (46%) regions, supporting sustained contractions during prolonged chewing activities, while type IIA and IIX fast-twitch fibers are more uniformly distributed.^[11] In terms of relations, the temporalis lies deep to the temporoparietal fascia and superficial to the lateral pterygoid muscle within the temporal fossa.^[1] Its tendon relates medially to the buccinator and laterally to the zygomatic arch as it descends. The muscle has a total physiological cross-sectional area of approximately 13-15 cm², enabling it to generate substantial force estimated at 150-300 N during contraction, which underscores its role in powerful jaw closure. The temporalis receives innervation via the deep temporal nerves, branches of the mandibular division of the trigeminal nerve (CN V3).^[1] Its posterior fibers also contribute to mandibular retrusion.^[1]

Medial pterygoid muscle

The medial pterygoid muscle is one of the four primary muscles of mastication, situated deep within the infratemporal fossa on the medial side of the mandible, where it contributes to elevating the jaw and facilitating medial deviation during chewing. This muscle adopts a quadrilateral shape and consists of two distinct heads: a superficial head originating from the maxillary tuberosity and the pyramidal process of the palatine bone, and a deep head arising from the medial surface of the lateral pterygoid plate of the sphenoid bone.^[12]^[13] The fibers from both heads converge to insert via a short tendon onto the medial surface of the ramus and angle of the mandible, extending up to the level of the mandibular foramen.^[12] Structurally, the medial pterygoid features short muscle fibers arranged in anteroposterior and mediolateral orientations, passing downward, laterally, and posteriorly at an oblique angle to the sagittal plane, which enables efficient force transmission for both vertical elevation and lateral grinding motions.^[12] In its upper third, the muscle is divided into three layers by intervening tendinous sheets, enhancing its mechanical stability.^[12] It exhibits a heterogeneous composition of fiber types, including slow-twitch, fast-twitch, and hybrid fibers.^[14]^[15] In terms of relations, the medial pterygoid lies immediately medial to the lateral pterygoid muscle and forms a functional sling with the masseter muscle across the mandibular ramus, collectively stabilizing the jaw during elevation.^[12] The lingual nerve courses lateral to its belly, while the nerve to the medial pterygoid—a branch of the mandibular division of the trigeminal nerve—enters from its medial surface to provide innervation (detailed further in the Innervation section).^[12]^[16] The muscle possesses a physiological cross-sectional area of approximately 3-5 cm², smaller than that of the masseter but sufficient to generate forces in the range of 100-200 N, making it particularly vital for unilateral chewing and load distribution on the working side of the mandible.^[17]^[18] This force capacity underscores its essential role in medial deviation of the mandible during lateral excursions (detailed in the Protrusion and lateral movements section).^[12]

Lateral pterygoid muscle

The lateral pterygoid muscle is a fan-shaped or conical muscle situated in the infratemporal fossa, uniquely divided into two distinct heads that contribute to its bilateral role in mandibular movement. The superior head is smaller and primarily tonic in function, while the inferior head is larger—approximately three times the size of the superior head—and phasic, with the muscle composed of a mixture of slow-twitch and fast-twitch fibers, reflecting the tonic function of the superior head and phasic function of the inferior head.^[19]^[18]^[20] The origin of the superior head arises from the infratemporal surface of the greater wing of the sphenoid bone and the infratemporal crest, while the inferior head originates from the lateral surface of the lateral pterygoid plate of the sphenoid bone. Both heads converge to insert into the pterygoid fovea located on the neck of the mandibular condyle and into the anterior aspect of the articular disc and capsule of the temporomandibular joint (TMJ), enabling direct influence on condylar and disc positioning.^[19] In terms of relations, the lateral pterygoid lies deep to the masseter muscle and the zygomatic arch, with its superior head in close proximity to the buccal nerve and the inferior head contributing to form the floor of the infratemporal fossa alongside the medial pterygoid. The muscle's physiological cross-sectional area (PCSA) totals approximately 3.8 cm² (inferior head: 2.82 ± 0.66 cm²; superior head: 0.95 ± 0.35 cm²), allowing it to generate forces in the range of 50-150 N based on typical skeletal muscle specific tension, which is essential for stabilizing the TMJ articular disc during movement.^[19]^[18]^[21] Innervation is provided by branches of the mandibular division of the trigeminal nerve (CN V3), and its primary role involves mandibular depression in coordination with other muscles.^[19]

Innervation and Vascular Supply

Innervation

The muscles of mastication—masseter, temporalis, medial pterygoid, and lateral pterygoid—are primarily innervated by the mandibular nerve (CN V3), the largest division of the trigeminal nerve (CN V), which serves as a mixed sensory and motor pathway originating from the pons.^[1] The mandibular nerve exits the skull through the foramen ovale and provides exclusive somatic motor innervation to these muscles, with no parasympathetic input, distinguishing it from certain other cranial nerve-innervated muscles such as those supplied by the oculomotor or facial nerves.^[22] Specific motor branches of the mandibular nerve target each muscle: the masseter receives innervation from the masseteric nerve, which arises from the anterior division of CN V3 and enters the muscle's deep surface; the temporalis is supplied by the anterior and posterior deep temporal nerves, also from the anterior division, which penetrate the muscle's deep aspect to reach its various layers.^[1]^[23] The medial pterygoid is innervated by the nerve to the medial pterygoid, a branch from the medial aspect of CN V3 that additionally supplies the tensor veli palatini muscle.^[1] The lateral pterygoid receives direct branches from CN V3, with the superior head typically innervated by a branch from the anterior division and the inferior head by a separate branch, often arising near the buccal nerve.^[19] The motor fibers originate in the trigeminal motor nucleus located in the dorsolateral tegmentum of the pons, where upper motor neurons from the corticobulbar tract synapse before descending via the motor root of CN V to join the mandibular division.^[22] These fibers exit through the foramen ovale to distribute to the masticatory muscles, enabling coordinated jaw movements. Sensory proprioceptive afferents from the muscles of mastication are carried via CN V3 but have their cell bodies uniquely located in the mesencephalic nucleus of the trigeminal nerve in the midbrain, bypassing the trigeminal ganglion and providing direct feedback on muscle stretch and tension to modulate motor output.^[24] Clinically, dysfunction in CN V3 innervation can manifest in conditions like trigeminal neuralgia, where irritation of the mandibular division may cause severe pain during mastication, leading to disuse atrophy of the affected muscles and preferential chewing on the contralateral side.^[25]^[26]

Blood supply

The muscles of mastication receive their primary arterial supply from the maxillary artery, the larger terminal branch of the external carotid artery, which courses through the infratemporal fossa to provide rich vascularization supporting their sustained contractile activity during chewing.^[1] The masseter muscle is supplied by the masseteric artery, a branch arising from the second part of the maxillary artery that passes through the mandibular notch to reach the deep surface of the muscle, with anastomoses to branches of the facial and transverse facial arteries.^[6] The temporalis muscle receives blood from the anterior and posterior deep temporal arteries, branches of the first part of the maxillary artery, along with contributions from the middle temporal artery, a branch of the superficial temporal artery, to its superficial fascia.^[27] The medial and lateral pterygoid muscles are both nourished by the pterygoid branches (inferior and superior, respectively) originating from the second part of the maxillary artery.^[3] Venous drainage from these muscles occurs primarily through the pterygoid venous plexus, a network of veins located within and around the lateral pterygoid muscle in the infratemporal fossa, which collects blood from the deep temporal, buccal, and pterygoid veins before draining posteriorly via the short maxillary vein into the retromandibular vein and ultimately the external jugular vein.^[28] This plexus communicates with the cavernous sinus via emissary veins through the foramen ovale and with the facial vein via the deep facial vein, creating potential pathways for retrograde infection spread from oral or facial infections to intracranial structures, such as in cases of cavernous sinus thrombosis.^[28] Lymphatic drainage from the muscles of mastication follows the vascular pathways and primarily reaches the submandibular lymph nodes, located in the submandibular triangle below the mandible, before proceeding to the deep cervical chain along the internal jugular vein; this route is clinically relevant for the spread of inflammatory processes from the masticatory region to the neck.^[29]

Function

Jaw elevation and depression

Jaw elevation, or closing of the mandible, is primarily achieved through the synergistic contraction of the masseter, temporalis (particularly its vertical fibers), and medial pterygoid muscles, which collectively generate force vectors that approximate the teeth and close the temporomandibular joint (TMJ).^[1] The masseter muscle provides the primary power for this action due to its robust structure and direct vertical pull on the mandibular ramus, enabling efficient force transmission during biting and chewing.^[30] These muscles are innervated by branches of the mandibular nerve (CN V3), ensuring coordinated activation to produce a total closing force of up to 700-900 N, with variations based on age, gender, and bite location.^[1]^[31] In contrast, jaw depression, or opening of the mandible, relies mainly on the bilateral contraction of the lateral pterygoid muscles, which pull the mandibular condyles forward and downward along the articular eminence of the TMJ, initiating the downward rotation and translation of the jaw.^[1] This action is assisted by gravity and the suprahyoid muscles (such as the digastric and geniohyoid).^[1] The lateral pterygoid's relatively weaker structure limits the total opening force to approximately 50-80 N, making depression less forceful than elevation and dependent on these auxiliary mechanisms for unresisted motion.^[32] The smooth coordination of these elevation and depression movements during mastication involves reciprocal inhibition mediated by trigeminal reflexes, where activation of jaw-opening muscles inhibits the closers via interneurons in the trigeminal motor nucleus, and vice versa, preventing simultaneous contraction and ensuring rhythmic cycles.^[33] These reflexes, elicited by sensory inputs from periodontal ligaments and muscle spindles, are processed through the trigeminal sensory and motor nuclei to modulate muscle activity for precise control.^[34]

Protrusion and lateral movements

Protrusion of the mandible, which advances the jaw forward to facilitate food manipulation, primarily involves the bilateral contraction of the inferior heads of the lateral pterygoid muscles, along with contributions from the superficial portions of the masseter and medial pterygoid muscles.^[1] These muscles pull the mandibular condyles anteriorly along the articular eminence of the temporomandibular joint (TMJ), enabling smooth forward translation of the mandible.^[35] The lateral pterygoid's attachment to the TMJ disc allows coordinated disc movement during this action.^[19] Lateral movements, or excursions, enable side-to-side grinding motions essential for mastication. These are achieved through the ipsilateral contraction of the medial pterygoid muscle combined with the contralateral inferior head of the lateral pterygoid, causing deviation of the mandible toward the opposite side.^[36] Additionally, the horizontal (posterior) fibers of the temporalis muscle assist in retrusion, helping to return the mandible to a neutral position after lateral deviation.^[1] Biomechanically, these movements involve a combination of rotation and translation at the TMJ, with the condyle rotating initially before sliding along the joint surfaces.^[35] Normal lateral excursions typically range from 8 to 12 mm, while protrusive movements cover 5 to 10 mm, allowing precise control during chewing.^[37]^[37] In the context of mastication, these muscles integrate through rhythmic alternation during chewing cycles, occurring at a frequency of 1 to 2 Hz to ensure efficient food breakdown.^[38] This coordination supports repetitive horizontal and oblique motions, optimizing grinding without excessive strain.^[1]

Development and Variations

Embryological origins

The muscles of mastication develop from the mesoderm of the first pharyngeal (mandibular) arch, which begins to form during the fourth week of gestation as part of the early embryonic head and neck structures.^[39] This arch mesoderm provides the core myogenic cells that will differentiate into the muscle precursors, while the surrounding ectomesenchyme, derived from neural crest cells migrating from the midbrain and hindbrain regions, supports the structural framework including connective tissues and skeletal elements associated with these muscles.^[40] By the fifth week, the first arch differentiates into maxillary and mandibular prominences, marking the onset of targeted myoblast proliferation within the mesodermal core.^[39] Neural crest cells play a critical role in the sensory and integrative components of these muscles' development, particularly through their contribution to the trigeminal ganglion formation around days 24–26 of gestation.^[22] These cells, originating near the rhombencephalon, invade the first pharyngeal arch and coalesce to form the sensory ganglia of the trigeminal nerve (cranial nerve V), which provides both sensory innervation to the oral cavity and motor outflow to the developing masticatory apparatus.^[22] The motor neurons, arising from the brainstem, extend axons into the arch mesenchyme concurrently, establishing early neuro-muscular connections that guide subsequent patterning.^[41] Myoblasts from the first arch mesoderm undergo migration starting in the fifth week, dispersing to form the distinct muscle bellies of the temporalis, masseter, and pterygoid muscles, with this process directed by the pioneering axons of the trigeminal nerve branches.^[39] This migration ensures precise positioning relative to the emerging skeletal elements, such as Meckel's cartilage.^[40] Differentiation of these first arch-derived muscles from those of the adjacent second arch is regulated by Hox gene expression patterns, notably the Hoxa2 boundary, where Hoxa2 is absent in the first arch mesoderm but expressed in the second, preventing homeotic transformations and specifying masticatory identity.^[42] By the seventh week of gestation, the primordia of the masticatory muscles become visible as condensed masses within the arch derivatives, with functional innervation via the mandibular division of the trigeminal nerve fully established by the eighth week.^[40] This timeline aligns with the broader craniofacial morphogenesis, ensuring coordinated development of the jaw apparatus.^[39]

Anatomical variations

The muscles of mastication exhibit notable anatomical variations that can influence their morphology, insertion points, and interactions with adjacent structures. These deviations from the typical configuration are observed across the masseter, temporalis, medial pterygoid, and lateral pterygoid muscles, often arising during development and detectable through imaging modalities such as MRI.^[43]^[44] In the masseter muscle, a deep head is frequently present but variably described, with classifications including a classical form separated by fascia, fusion with the medial pterygoid, or segmentation into multiple bellies; these forms contribute to vertical bite force and mandibular stabilization, though specific prevalence rates remain underreported due to small sample sizes in studies. Accessory slips from the deep masseter head may extend to the buccinator fascia or temporalis tendon, representing rare developmental anomalies that could alter local force distribution during chewing.^[43]^[45]^[45] The temporalis muscle shows variability in its deep portion, which is sometimes absent or inconsistently described in anatomical literature, potentially affecting insertion breadth and innervation patterns; a systematic review indicates diverse branching of the deep temporal nerves, with up to three primary divisions entering the muscle belly, influencing its role in jaw elevation. Shape variations, such as digastric-like or pentagonal bellies, have been noted anecdotally but lack quantified prevalence, possibly impacting the muscle's fan-shaped insertion on the coronoid process.^[46] Pterygoid muscles demonstrate the highest variability, particularly the lateral pterygoid, where a two-headed configuration (superior and inferior) predominates at approximately 74%, while a single-headed form—often lacking a distinct inferior head—occurs in about 11%, and three-headed variants in 14%; these differences in head number and attachments to the temporomandibular joint disc-condyle complex can modify protrusive movements and joint stability. The medial pterygoid occasionally presents as duplicated or with accessory slips, though such cases are infrequently quantified and may blend fibers with adjacent muscles, potentially complicating surgical approaches.^[47]^[48] Facial asymmetry associated with masticatory muscle size and activity differences is reported in 12-37% of orthodontic patients, often linked to facial skeletal discrepancies, which can lead to uneven loading on the temporomandibular joint (TMJ). Such variations may reduce bite force efficiency or increase TMJ compressive loads by 20-30% during asymmetric biting, as modeled in subjects with disc displacement.^[49] Genetic factors contribute to more pronounced variations in craniofacial syndromes; for instance, Treacher Collins syndrome, caused by mutations in TCOF1 (81-93% of cases), results in mandibular and zygomatic hypoplasia that indirectly affects masticatory muscle attachment sites and function, leading to reduced muscle mass and feeding difficulties. These syndrome-related changes highlight how genetic disruptions in neural crest cell development can exacerbate normal variations into clinically significant forms.^[50]^[51]

Clinical Significance

Disorders and dysfunctions

Myofascial pain syndrome is a common condition affecting the muscles of mastication, characterized by the presence of trigger points in muscles such as the masseter and temporalis, often resulting from overuse due to parafunctional activities like clenching or prolonged chewing.^[52] These trigger points can cause localized tenderness and referred pain that radiates to areas like the jaw, ear, or teeth, contributing to chronic orofacial discomfort.^[52] The lifetime prevalence in the general adult population is estimated at 3-15%, with higher rates among women and peaking in ages 18-44 years.^[52] Trismus, or restricted mouth opening, frequently arises from spasms in the pterygoid muscles, particularly the medial pterygoid, leading to painful limitation of mandibular movement.^[53] A common etiology is post-dental extraction, such as after third molar removal, where surgical trauma induces an inflammatory response and reflex muscle contraction.^[53] This spasm can persist for days to weeks, impairing functions like eating and speaking.^[53] Temporomandibular disorders (TMD) often involve hyperactivity of the masticatory muscles due to bruxism, a parafunctional habit of teeth grinding or clenching that overloads muscles like the masseter and temporalis.^[54] This chronic muscle tension can lead to hypertrophy, where muscles increase in size and strength, or contribute to temporomandibular joint disc displacement through sustained mechanical stress.^[54] Bruxism-related TMD affects approximately 5-12% of adults, predominantly those aged 20-40, with women more commonly impacted.^[54] Neurological disorders such as pure trigeminal motor neuropathy can cause weakness in the masticatory muscles by affecting the motor branch of the trigeminal nerve, without sensory involvement.^[55] This rare condition often presents with unilateral atrophy, particularly of the masseter muscle, visible on imaging as fatty infiltration and reduced muscle volume, alongside electromyographic evidence of neurogenic changes.^[55] Traumatic injuries to the muscles of mastication, such as contusions from mandibular or zygomatic fractures, commonly occur in high-velocity impacts like motor vehicle accidents.^[56] These contusions may involve the pterygoid plexus, leading to hematoma formation that exacerbates swelling and restricts jaw mobility.^[56]

Diagnostic and treatment approaches

Diagnosis of disorders affecting the muscles of mastication typically begins with a clinical examination, including palpation to assess tenderness and trigger points in the masticatory muscles such as the masseter and temporalis.^[54] Goniometry is employed to measure the range of motion in jaw opening and lateral excursions, helping to quantify functional limitations. Imaging modalities play a crucial role; magnetic resonance imaging (MRI) is used to detect muscle edema and structural abnormalities in the temporomandibular joint (TMJ) and surrounding tissues.^[54] Ultrasound serves as a non-invasive tool for identifying trigger points and myofascial changes in the masticatory muscles.^[57] Electromyography (EMG) evaluates muscle activity patterns, providing insights into abnormal firing and coordination during jaw movements.^[54] Treatment approaches for masticatory muscle disorders emphasize conservative and multidisciplinary strategies, particularly for temporomandibular disorders (TMD). Occlusal splints are a primary conservative intervention, designed to reduce muscle strain by stabilizing the occlusion and alleviating bruxism-related tension.^[58] Physiotherapy, including manual therapy and exercises, targets muscle relaxation and improved jaw mobility in TMD management.^[59] Pharmacological options commonly include nonsteroidal anti-inflammatory drugs (NSAIDs) to manage pain and inflammation, alongside muscle relaxants to address spasms in the masticatory muscles.^[54] For cases of masseter hypertrophy, botulinum toxin injections offer an effective, minimally invasive treatment by inducing targeted muscle atrophy and reducing bulk.^[60] In severe or refractory cases, surgical interventions may be necessary, required in only a small minority of chronic TMD patients. Myotomy of the masticatory muscles, often combined with coronoidectomy, is performed to release trismus and restore mouth opening.^[61] TMJ arthroscopy addresses internal derangements, such as disc displacement, by allowing visualization and minimally invasive repair within the joint space.^[62] Preventive measures focus on addressing predisposing factors like malocclusion through orthodontic correction, which helps redistribute occlusal forces and minimize chronic strain on the masticatory muscles.^[63]

References

[1]
Anatomy, Head and Neck, Mastication Muscles - StatPearls - NCBI
The primary muscles of mastication (chewing food) are the temporalis, medial pterygoid, lateral pterygoid, and masseter muscles. The four main muscles of ...Introduction · Nerves · Muscles · Clinical Significance
[2]
The parotid, temporal and infratemporal regions
The muscles of mastication are the masseter, temporalis, medial pterygoid and lateral pterygoid. They are all supplied by the mandibular nerve, a division of ...
[3]
Muscles of mastication: Anatomy, functions, innervation | Kenhub
Definition and function, The muscles of mastication are muscles that attach to the mandible and thereby produce movements of the lower jaw. MusclesTemporalis Muscle · Masseter Muscle · Lateral Pterygoid Muscle
[4]
Anatomy of the temporomandibular joint and muscles of mastication
Anatomy of the temporomandibular joint and muscles of mastication ... Additionally, the TMJ also allows for gliding and rotation. The articular components ...
[5]
The cost of chewing: The energetics and evolutionary significance of ...
Aug 17, 2022 · Our ancestors' ability to effectively acquire, process, and consume food underpinned their survival, and changes in their masticatory system ...
[6]
Anatomy, Head and Neck, Masseter Muscle - StatPearls - NCBI
The masseter muscle is one of the muscles of mastication. It is a powerful superficial quadrangular muscle with two divisions: superficial and deep.Missing: primary | Show results with:primary
[7]
Human Masseter Muscle Fiber Type Properties, Skeletal ... - NIH
Our findings suggest that there are gender differences between fiber type size and growth factor gene expression levels (Fig 5).
[8]
Study of human adult parotid duct in the area of penetration through ...
From the parotid gland, parotid duct traverses through masseter muscle, penetrates through buccinator muscle, and opens into the oral cavity. This unique form ...
[9]
Physiological cross-section of the human jaw muscles - PubMed
The cross-sectional areas of the masseter, temporalis, medial pterygoid and lateral pterygoid muscles were determined by means of computer tomography.<|separator|>
[10]
Regional differences in fibre type composition in the ... - PubMed
Type I fiber number varies: 24% in the posterior, 57% in the intermediate, and 46% in the anterior temporalis muscle. Type IIA and IIX proportions are constant.
[11]
Anatomy, Head and Neck, Medial Pterygoid Muscle - NCBI - NIH
The medial pterygoid muscle, a major elevator of the jaw is a square-shaped masticatory muscle, located on the medial aspect of the lower jaw bilaterally.
[12]
Medial pterygoid muscle - Kenhub
Medial pterygoid muscle consists of two heads; superficial and deep, that are separated by the inferior head of lateral pterygoid muscle at their origin.
[13]
Histochemical and morphological muscle-fibre characteristics of the ...
The study found marked variability in muscle-fiber composition, with a large proportion of ATPase intermediate fibers and rare type IIA fibers. The fiber ...
[14]
Myosin isoform composition of the human medial and lateral ...
The study found no significant difference in myosin isoform composition between medial and lateral pterygoid muscles, despite their different functions.
[15]
Anatomy, Head and Neck, Medial (Internal) Pterygoid Nerve - NCBI
The motor root via its various branches provides special visceral efferent (branchiomotor) innervation to various muscles, including medial pterygoid, tensor ...Structure and Function · Embryology · Nerves · Muscles
[16]
Relationships between the size and spatial morphology of human ...
The masseter muscle was about 66% larger in cross section than the medial pterygoid and was inclined more anteriorly relative to the functional occlusal plane.
[17]
Architecture of the Human Pterygoid Muscles - PubMed
Muscle force is proportional to the physiological cross-sectional area (PCSA), and muscle velocity and excursion are proportional to the fiber length.Missing: generation | Show results with:generation
[18]
Anatomy, Head and Neck, Lateral Pterygoid Muscle - NCBI - NIH
Sep 10, 2024 · The lateral pterygoid muscle is a single unit divided into 2 bellies with clearly identified anterior insertions and posterior attachments that ...Missing: size strength
[19]
Fiber-type Composition of the Human Jaw Muscles - ResearchGate
Aug 8, 2025 · ... lateral pterygoid) differs from that of the jaw-. opening muscles. A ... faster, phasic movements. The differences in fiber-type ...
[20]
Architecture of the human jaw‐closing and jaw‐opening muscles
No readable text found in the HTML.<|separator|>
[21]
Neuroanatomy, Cranial Nerve 5 (Trigeminal) - StatPearls - NCBI - NIH
Apr 20, 2024 · CN V3 also gives off branches that innervate the tensor veli palatini, mylohyoid, tensor tympani, and anterior digastric belly. Go to: Surgical ...
[22]
Temporalis: Origin, insertion, innervation, function | Kenhub
The temporalis muscle is the strongest muscle of the temporomandibular joint and the primary retractor of the mandible.
[23]
Neuroanatomy, Trigeminal Nucleus - StatPearls - NCBI Bookshelf
May 1, 2023 · In contrast, the mesencephalic nucleus contains cell bodies of neurons associated with processing input related to proprioception involved with ...
[24]
Trigeminal Neuralgia - StatPearls - NCBI Bookshelf - NIH
Mar 3, 2024 · Mandibular (V3): lower lip, lower gingivae, jaw, and the muscles of mastication. Most cases of trigeminal neuralgia are secondary to ...
[25]
Changes in the muscles of mastication before and after primary ...
Nov 8, 2019 · The study objective was to evaluate the changes in the muscles of mastication before and after upfront GKRS in patients with idiopathic TN by using MRI.
[26]
The Muscles of Mastication - Attachments - Actions - Innervation - TeachMeAnatomy
### Blood Supply and Venous Drainage of Muscles of Mastication
[27]
Neuroanatomy, Pterygoid Plexus - StatPearls - NCBI Bookshelf
Posteriorly, the pterygoid plexus drains via the maxillary vein. The maxillary vein joins the superficial temporal vein to become the retromandibular vein ...Introduction · Structure and Function · Embryology · Blood Supply and Lymphatics
[28]
Lymphatic Drainage of the Head and Neck - TeachMeAnatomy
### Summary of Lymphatic Drainage of the Face, Jaw, and Muscles Around the Mandible/Mastication Area
[29]
Muscles of Mastication - an overview | ScienceDirect Topics
The large masseter and temporalis are powerful elevators of the mandible (Figure 3), assisted by the pterygoid medialis. The pterygoid lateralis, assisted by ...
[30]
[PDF] Reliability, reference values and factors related to maximum bite ...
Results The intraclass correlation coefficient for the MBF was 0.90, with 10th to 90th percentiles of 487–876 N for females and 529–1003 N for males. A positive ...
[31]
Mathematical Model of the Human Jaw System Simulating Static ...
(resulting in an increase in jaw-opening force) is possibly have moved 4.5 mm ... We submit that of the lateral pterygoid muscle (Yoshida and Inoue 1995).
[32]
Human jaw reflexes - PubMed
The jaw-opening reflex (including exteroceptive suppression of jaw-closer muscle activity) is bilaterally symmetrical rather than bilaterally reciprocal, as are ...
[33]
The reciprocal jaw-muscle reflexes elicited by anterior
Dec 17, 2020 · Tooth-contact sensations are considered essential to boost jaw adductor muscles during mastication. However, no previous studies have explained the importance ...
[34]
Anatomy, Head and Neck, Temporomandibular Joint - NCBI - NIH
Originating from the zygomatic arch with multiple muscular layers, the masseter inserts on the lateral surface of the mandibular ramus and the lateral surface ...
[35]
[PDF] 3D Modeling and Animation of the Temporomandibular Joint (TMJ ...
Apr 25, 2018 · There are five major muscles involved in mastication. These include the temporalis, the masseter, the medial pterygoid, the lateral pterygoid, ...
[36]
[PDF] Functional Analysis Of Mandibular Movements In Three Different ...
The lateral excursion refers to the sideways movement of the lower jaw 12,30,35,38,43,53. The normal lateral excursive movement ranges from 8 mm to 12 mm on ...
[37]
Anatomical, functional, physiological and behavioural aspects of the ...
The mastication apparatus is composed of four major components: bones, muscles, teeth and soft tissues, which are described below. It is important to first ...
[38]
Embryology, Face - StatPearls - NCBI Bookshelf
Jan 30, 2024 · Myoblasts from the 1st pair of pharyngeal arches produce the mastication muscles, while myoblasts from the 2nd pair of pharyngeal arches ...
[39]
Pharyngeal arches - UNSW Embryology
Feb 23, 2022 · Hox genes in the pharyngeal region: how Hoxa3 controls early embryonic development of the pharyngeal organs "The pharyngeal organs ...<|control11|><|separator|>
[40]
Origins and Innervations of Pharyngeal Arch and Somite Myotome ...
Jul 3, 2016 · The muscles of branchiomeric origin retain their original cranial nerve innervation as they migrate to their final destinations (see Plates 1-20 ...<|control11|><|separator|>
[41]
Differing contributions of the first and second pharyngeal arches to ...
Sep 15, 2017 · We visualize the boundary between PA1 and PA2 by examining Hoxa2 expression to compare the position of the forming TM in mouse and chick embryos ...
[42]
https://journals.biologists.com/dev/article/144/18/3315/47970/Differing-contributions-of-the-first-and-second
[43]
Variations of the attachment of the superior head of human lateral ...
This study demonstrates that there are three different attachment types of the SLPM to the disc-condyle complex. The type III variation could be involved in ...
[44]
The Deep Head of the Masseter Muscle: A Classification-Based ...
In rare cases, accessory slips from the DHMM were found to insert onto the temporalis tendon or buccinator fascia, suggesting unusual developmental trajectories ...Missing: prevalence | Show results with:prevalence
[45]
[PDF] Deep portion of the human temporalis muscle - MedCrave online
Oct 21, 2025 · The deep portion of the temporalis muscle has historically been either omitted from anatomical literature or described with variability.Missing: variations | Show results with:variations
[46]
(PDF) Morphological Spectrum of the Lateral Pterygoid Muscle
Oct 1, 2025 · During the original study, the two-headed configuration was most common (74.4%), followed by three-headed (14%), one-headed (10.8%), and four- ...
[47]
Facial Asymmetry: A Narrative Review of the Most Common ... - MDPI
Apr 4, 2022 · The prevalence of facial asymmetry ranges from 21% to 85% [134]. In a group of orthodontic patients, asymmetry ranged from 12% to 37% [135,136].
[48]
Human mandibular shape is associated with masticatory muscle force
Apr 16, 2018 · The aims of this study were to identify associations between masticatory muscle force (as estimated by CSAs) and mandibular shape and to relate ...Missing: TMJ | Show results with:TMJ
[49]
Treacher Collins syndrome: MedlinePlus Genetics
Dec 9, 2022 · TCOF1 gene variants are the most common cause of the disorder, accounting for 81 to 93 percent of all cases. POLR1C and POLR1D gene variants ...
[50]
Treacher Collins Syndrome - GeneReviews® - NCBI Bookshelf - NIH
Jul 20, 2004 · Hypoplasia of the zygomatic bones, maxilla, and mandible can cause significant respiratory and feeding difficulties.
[51]
Clinical aspects of mastication myalgia—an overview - PMC
Jan 9, 2024 · However, research suggests that it is a relatively common condition worldwide and the lifetime prevalence is between 3% and 15% in the general ...
[52]
Trismus - StatPearls - NCBI Bookshelf - NIH
Oct 27, 2022 · Trismus is commonly referred to as lockjaw and is usually due to sustained tetanic spasms of the muscles of mastication.
[53]
Temporomandibular Syndrome - StatPearls - NCBI Bookshelf - NIH
Jan 30, 2023 · The muscles involved in temporomandibular disorders are the muscles of the mastication: temporalis, masseter, medial and lateral pterygoid ...
[54]
Unilateral masticatory atrophy caused by pure trigeminal motor ... - NIH
Sep 27, 2022 · We describe a rare case of an 83-year-old man with weakness and atrophy of the right masticatory muscle without any sensory disturbance.Missing: prevalence | Show results with:prevalence
[55]
Maxillofacial Injuries | Musculoskeletal Key
Jun 12, 2016 · The presence of trismus may indicate a hematoma or contusion ... injury is much higher with this injury than with other types of facial fractures.<|control11|><|separator|>
[56]
myofascial temporomandibular disorder: Topics by Science.gov
... disorders. In patients with long-term dysfunction of masticatory muscles, the palpation examination can localize trigger points, that is, thickening in the ...
[57]
temporomandibular joint osteoarthritis: Topics by Science.gov
Magnetic resonance imaging can be employed to detect bone marrow edema even in the absence of pain and clinical symptoms in the patients of internal ...
[58]
[PDF] 10th Annual Research Symposium - Abstracts
Feb 21, 2024 · The evaluation of muscle activity and dysfunction is conducted through electromyography (EMG) and jaw-tracking devices by healthcare ...<|separator|>
[59]
Management of pain in patients with temporomandibular disorder ...
Conservative treatments for TMD include medication, physiotherapy, occlusal splints, self-management strategies, and interventions based on cognitive ...
[60]
[PDF] Topic Brief: Temporomandibular Disorder Treatment Guidelines
Feb 7, 2023 · diverse drugs, occlusal splints, oral analgesics, self-exercise, massage, or health instruction 16. • Acupuncture, physiotherapy, low- level ...
[61]
Study Details | Management of Temporomandibular Disorders (TMD)
Conservative management of TMD treatment includes occlusal splints; physical therapy; oral medication (NSAIDs and muscle relaxants); and orthodontic treatment.Missing: physiotherapy | Show results with:physiotherapy
[62]
Botulinum Toxin Injection for Masseteric Hypertrophy Using 6 Point ...
Mar 21, 2023 · Botulinum toxin-A injection is a non-invasive, safe, and effective treatment for masseter muscle hypertrophy. The 6-point injection technique ...
[63]
The Effectiveness of Surgical Methods for Trismus Release at Least ...
Three treatment strategies were identified for trismus release (1) free flap reconstruction (FFR), (2) coronoidectomy (CN), and (3) myotomy (MT).Missing: arthroscopy | Show results with:arthroscopy
[64]
Complications of Temporomandibular Joint Surgery - Academia.edu
56.1% of headache disorder patients have concomitant TMD; 80% of TMD patients report headaches. TMJ surgery can reduce headache frequency by over 50%, but not ...
[65]
Malocclusion of teeth: MedlinePlus Medical Encyclopedia
Mar 31, 2024 · Eliminate strain on the teeth, jaws, and muscles. ... Call your dentist if toothache, mouth pain, or other new symptoms develop during orthodontic ...