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Muscles of Mastication

Original Editor - Olajumoke Ogunleye

Top Contributors - Olajumoke Ogunleye, Wendy Walker, Joao Costa, Kim Jackson, Vidya Acharya, Areeba Raja, Ahmed M Diab and Alexandra Stead

Introduction and Overview

Overview of the muscles of mastication
Overview of the muscles of mastication

The muscles of mastication are a group of muscles responsible for the chewing movement of the mandible at the temporomandibular (TMJ) joint, they enhance the process of eating, assist in chewing food, and also function to approximate the teeth.[1] [2] The four main muscles of mastication originate from the surface of the skull and they attach onto the rami of the mandible at the TMJ. The movement performed by these muscles are elevation, depression, protrusion, retraction, and side to side movement. Three out of the four main muscles contribute to elevation (closing) of the mandible; the lateral pterygoid is the primary contributor to depression (opening) of the mandible.[3]

Unlike the muscles of facial expression that are innervated by the facial nerve (CN VII), the muscles of mastication are innervated by motor branches of the mandibular division of the trigeminal nerve (CNV3), while the main arterial supply is derived from branches of the maxillary artery.

Image: Overview of the muscles of mastication[4]

Muscles of mastication

The muscles of mastication can be divided into the primary muscles and secondary or accessory muscles[3] [5].

  1. The primary muscles include:
  2. The secondary or accessory muscles are:

Embryology

The muscles of mastication develop from the first pharyngeal arch, and as a result they share a common innervation by the mandibular branch of the trigeminal nerve (CNV3).[3][6]

Masseter

Masseter

Masseter[7] is a rectangular muscle that covers most of the lateral aspect of the ramus. It consists of two layers that blend anteriorly: the superficial layer, and deep layer.

Origin and Insertion

The deep fibres of the muscle originate from the posterior third of the inferior aspect of the zygomatic arch as well as the zygomatic process of the maxilla; the superficial fibres arise from the temporal process of the zygomatic bone and the anterior two-thirds of the inferior border of the zygomatic arch.

The fibres from both layers converge inferiorly to insert at the outer surface of the mandibular ramus and the coronoid process of the mandible.

Nerve and blood supply

It is innervated by the masseteric nerve, which is a branch of the mandibular nerve (V3) of the trigeminal nerve. Its blood supply is from the pterygoid branch of the 2nd part of the maxillary artery.

Function

  • The major function of the masseter muscle is to elevate the mandible.
  • The deep fibres of masseter function to retract the mandible and the superficial fibres function to protrude the mandible. The deep fibres are important stabilisers of the TMJ.

Temporalis

Temporalis

Temporalis[3] is a fan-shaped muscle that fills the temporal fossa, with anterior fibres that have a vertical orientation, mid fibres have an oblique orientation, and posterior fibres have more of a horizontal orientation.

Origin and Insertion

It originates from the temporal fossa to the inferior temporal line of the lateral skull. The temporalis muscle fibres converge inferiorly forming a tendon that exits the temporal fossa passing underneath the zygomatic arch and inserting on the coronoid process of the mandible.

Nerve and blood supply

  • It is supplied by the deep temporal nerve which is a branch from the anterior division of the mandibular nerve.
  • Blood supply of the temporalis muscle is from the deep temporal part of the maxillary artery and the middle temporal branches of the superficial temporal artery.

Function

  • The function of the anterior and mid fibres of the temporalis muscle is to elevate the mandible.
  • The posterior fibres of the temporalis muscle function to retract the mandible. It also contributes to side to side grinding movement.

Medial Pterygoid

Medial pterygoid

The medial pterygoid muscle[8] is a thick rectangular muscle with a superficial head and a deep head. The deep head of the medial pterygoid is larger than the superficial head.

Origin and Insertion

  • The superficial head of the medial pterygoid has its origin from the maxillary tuberosity of the inferior maxilla and the deep head originates from the medial surface of the lateral pterygoid plate of the sphenoid bone.
  • The medial pterygoid muscle fibres converge inferiorly and insert onto the medial aspect of the mandible. The insertion of the medial pterygoid forms a tendinous band with the insertion of the masseter called the pterygoid-masseteric sling.

Nerve and blood supply

  • It is innervated by the medial pterygoid nerve, a branch of the mandibular nerve.
  • Its blood is supplied by a pterygoid branch of 2nd part of the maxillary artery (CN V3).

Function

The medial pterygoid muscle functions to assist with elevation and protrusion of the mandible. It also assists the lateral pterygoid muscle with side to side mandibular motion to help with the grinding of food.

Lateral Pterygoid

Lateral Pterygoid

The lateral pterygoid[9] [10] is a short thick muscle with two heads: superior and inferior heads.

Origin and Insertion

  • The superior head arises from the inferior temporal surface of the greater wing of the sphenoid bone. The inferior head arises from the lateral surface of the lateral pterygoid plate of the sphenoid bone.
  • The lateral pterygoid muscle fibres converge inferiorly, forming a tendon that inserts into a depression; pterygoid fovea of the neck of the condylar process of the mandible along with the articular capsule and disc of the temporomandibular (TMJ) joint.

Nerve and blood supply

  • The lateral pterygoid is supplied by a branch of the anterior division of the mandibular nerve.
  • Its blood supply is from the pterygoid branch of 2nd part of the maxillary artery.

Function

  • The lateral pterygoid muscle functions as the sole muscle of mastication to causes depression of the mandible. This being the case, depression of the mandible is largely the result of gravity.
  • It also assists with protrusion and side to side movement of the mandible.

Accessory Muscles of Mastication

Suprahyoid muscles

The suprahyoid muscle group[9] [10] is made up of the digastric muscle, mylohyoid muscle, and geniohyoid muscle. They depress the mandible against resistance when infrahyoid muscles fix or depress the hyoid bone.

Infrahyoid muscles

The infrahyoid muscles[9][10] are made up of the omohyoid, sternohyoid, sternothyroid, and thyrohyoid. They fix or depress the hyoid bone.

Buccinator

The buccinator is a facial expression muscle that helps in mastication by keeping food pushed back within the oral cavity.

For full details of nerve and vascular supply please see the Facial Muscles - Lower Group page.

Clinical relevance

The following clinical presentations are recognised within masticatory muscle disorder classifications.[11]

Masticatory Myofascial pain[12]: Mastication muscle pain disorders are similar to other skeletal muscle disorders in other parts of the body. Myofascial pain is characterised by a dull regional ache with the presence of trigger points when palpated which produces referred pain, that increases during the function.

Masticatory myalgia: This is characterised as a dull persistent ache overlying the jaw and temple muscles with occasional reference to other structures such as head, neck, ear, and teeth. Symptoms can also include a restricted opening, fatigue, and stiffness. Signs include tenderness of the muscles with limited ROM. Localised myalgia presents as sore or aching muscles, usually affecting bilaterally at the region of masseter and temporalis muscles.[11]

Masticatory myospasm[13]: Myospasm also known as muscle cramp is an acute condition resulting from a sudden, involuntary and continuous tonic contraction of the muscle. It is characterised by acute shortening of a single muscle and may lead to trismus (lockjaw), pain on movement, severely limited range of movement of the mandible. These characteristics coupled with their sudden onset at rest allow the clinician to differentiate myospasm from other masticatory muscle disorders.

Myofibrotic contracture[14]: This involves a painless shortening of muscle as a result of fibrosis in and around the remaining contractile muscle tissue. It frequently follows an infectious process or trauma. There is limited mouth opening and unyielding resistance to passive jaw muscle stretch.

Myositis[15]: Myositis is an inflammatory condition of the muscles caused by acute trauma or infection; it may also occur as part of a systemic inflammatory condition. It is characterized by swelling, redness overlying skin and increases the temperature over the affected area. It results in jaw dysfunction and limited range of movement.

Bruxism: Bruxism consists of an involuntary, aimless, repetitive, stereotyped oral activity characterised by teeth clenching or grinding. The disorder is heterogeneous and distinguishes wakeful from sleep bruxism. Wakeful bruxism arises in a variety of psychological, neurological, and orodental conditions. Sleep bruxism can occur during all stages of sleep, light sleep in particular. Bruxism is important to recognise and monitor because of the extremely powerful forces exerted on teeth, periodontal structures, temporomandibular joint, and masticatory muscles, often causing tooth wear and destruction, temporomandibular joint and muscle pain, as well as tension-type headache. The sleeper is unaware of the jaw activity, but the grinding noise can disrupt the sleep of the bedroom partner and cause social embarrassment.[16]

Temporomandibular joint (TMJ) dysfunction: TMJ dysfunction can result from an imbalance of forces within the muscles of mastication.[3] Grinding of teeth at night (bruxism) is a common cause of TMJ dysfunction secondary to a resultant imbalance in the muscle of mastication forces from excessive grinding of the teeth.

Tumours: Although rare, tumours may present in the masticator space[17], which is enveloped by the deep cervical fascia, and may extend from adjacent regions.

Assessment

Assessment of the muscles of mastication is relevant in the management of temporomandibular dysfunction (TMD), cervicogenic headache and orofacial pain. A thorough assessment includes observation, palpation, range of movement testing and muscle strength testing.[11] Evaluation of the muscles of mastication also contributes to evaluation of the trigeminal nerve (CN V) in a neurological examination.[18]

Muscle Strength Testing

The masseter can be assessed by having the patient clench the jaw and evaluating the volume and firmness of the muscle bilaterally.[18] The pterygoid muscles are assessed by asking the person to move the jaw laterally against resistance and to protrude the jaw. Weakness of the pterygoid muscles causes deviation of the open jaw to the ipsilateral side.

The other muscle of mastication supplied by the trigeminal nerve, the pterygoids, are examined by having the patient move the jaw from the side against resistance, and protrude the jaw. Contraction of each muscle causes deviation of the jaw to the opposite side so that the weakness of the pterygoid muscles would cause deviation of the open jaw to the ipsilateral side.[18][19]

Range of Movement

Jaw range of movement should be assessed[11][20], including:

  • Maximum unassisted mouth opening (normal:40-50mm)
  • Maximum assisted mouth opening
  • Lateral excursion (normal: 8-12mm each side)
  • Protrusion (normal: 6-9mm)

Note that deviation or deflection during opening may indicate muscular asymmetry or intra-articular pathology.[3][21]

Palpation

Palpation of the masseter and temporalis can be performed extraorally. The medial and lateral pterygoids require intraoral access and are typically assessed by a suitably trained clinician. Palpation should assess for tenderness, trigger points and muscle bulk. For detailed palpation and soft tissue mobilisation techniques, see TMJ and Muscles of Mastication.

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Physiotherapy Management

Physiotherapy management of masticatory muscle dysfunction is typically multimodal and may include:

  • Manual therapy: soft tissue mobilisation, trigger point release and joint mobilisation of the TMJ
  • Therapeutic exercise: jaw opening and closing control exercises, stretching and postural correction
  • Dry needling: evidence supports its use for myofascial trigger points in masseter and temporalis
  • Education and self-management advice on parafunctional habits (e.g. clenching, bruxism), jaw rest and diet modification
  • Addressing contributing factors: cervical spine dysfunction, forward head posture and breathing pattern disorders

A multimodal approach that considers the broader musculoskeletal and nervous system context is recommended.[22][12] For detailed management guidance, see Temporomandibular Disorders and TMJ and Muscles of Mastication.

References

  1. ↑ Alomar X, Medrano J, Cabratosa J, Clavero JA, Lorente M, Serra I, Monill JM, Salvador A. Anatomy of the temporomandibular joint. Semin Ultrasound CT MR. 2007 Jun;28(3):170-83. doi: 10.1053/j.sult.2007.02.002. PMID: 17571700.
  2. ↑ Yost O, Liverman CT, English R, et al., editors. Temporomandibular Disorders: Priorities for Research and Care. Washington (DC): National Academies Press (US); 2020 Mar 12. Appendix D, Masticatory System: Anatomy and Function. National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division; Board on Health Care Services; Board on Health Sciences Policy; Committee on Temporomandibular Disorders (TMDs): From Research Discoveries to Clinical Treatment;
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Basit H, Tariq MA, Siccardi MA. Anatomy, Head and Neck, Mastication Muscles. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jun 5.
  4. ↑ Overview of the muscles of mastication image - © Kenhub https://www.kenhub.com/en/library/anatomy/the-muscles-of-mastication
  5. ↑ Nelson SJ. Wheeler's dental anatomy, physiology and occlusion.10th edition. Elsevier Health Sciences, 2014.
  6. ↑ Yamane A. Embryonic and postnatal development of masticatory and tongue muscles. Cell Tissue Res. 2005 Nov;322(2):183-9. doi: 10.1007/s00441-005-0019-x. Epub 2005 Nov 3. PMID: 16041600.
  7. ↑ Corcoran NM, Goldman EM. Anatomy, Head and Neck, Masseter Muscle. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jun 5
  8. ↑ Bhojwani V, Ghabriel MN, Mihailidis S, Townsend GC. The human medial pterygoid muscle: Attachments and distribution of muscle spindles. Clin Anat. 2017 Nov;30(8):1064-1071. doi: 10.1002/ca.22947. Epub 2017 Jul 27. PMID: 28639342.
  9. ↑ 9.0 9.1 9.2 Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 8th ed. Philadelphia: Wolters Kluwer; 2018.
  10. ↑ 10.0 10.1 10.2 Standring S, editor. Gray's Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. Edinburgh: Elsevier; 2021.
  11. ↑ 11.0 11.1 11.2 11.3 Schiffman E, Ohrbrach R, Truelove E, et al. Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) for Clinical and Research Applications. J Oral Facial Pain Headache. 2014; 28(1):6-27.
  12. ↑ 12.0 12.1 Fernandez-de-las-Penas C, Svensson P. Myofascial Temporomandibular Disorder. Curr Rheumatol Rev. 2016;12(1):40-54.
  13. ↑ Fu KY, Zhang W, Cao Y, Kang YF, Xie QF. [Classification and clinical characteristics of masticatory myospasm]. Zhonghua Kou Qiang Yi Xue Za Zhi. 2012 Jul;47(7):423-6. Chinese. doi: 10.3760/cma.j.issn.1002-0098.2012.07.011. PMID: 22931574.
  14. ↑ Okeson JP. Treatment of Chronic Mandibular Hypomobility and Growth Disorders. In: Orofacial Pain: Guidelines for Assessment, Diagnosis, and Management. Pocket Dentistry, 2015
  15. ↑ Kim HG, Lee JH, Lee H, et al. Infectious myositis of the jaw presenting as trismus of unknown origin. J Oral Med Pain. 2020;45(4):115–121.
  16. ↑ Lobbezoo F, Ahlberg J, Raphael KG, Wetselaar P, Glaros AG, Kato T, Santiago V, Winocur E, De Laat A, De Leeuw R, Koyano K, Lavigne GJ, Svensson P, Manfredini D. International consensus on the assessment of bruxism: Report of a work in progress. J Oral Rehabil. 2018 Nov;45(11):837-844. doi: 10.1111/joor.12663. Epub 2018 Jun 21. PMID: 29926505; PMCID: PMC6287494.
  17. ↑ Fernandes T, Lobo JC, Castro R, Oliveira MI, Som PM. Anatomy and pathology of the masticator space. Insights Imaging. 2013 Oct;4(5):605-16. doi: 10.1007/s13244-013-0266-4. Epub 2013 Jul 27. PMID: 23888350; PMCID: PMC3781239.
  18. ↑ 18.0 18.1 18.2 Gilden DH. Cranial Nerve V: The Trigeminal Nerve. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical and Laboratory Examinations. 3rd ed. Boston: Butterworths; 1990. Chapter 61.
  19. ↑ Ghatak RN, Helwany M, Ginglen JG. Anatomy, Head and Neck, Mandibular Nerve. In: StatPearls [Internet]. StatPearls Publishing; 2023.
  20. ↑ Magalhaes BG, de Sousa ST, de Mello VV, da Silva CE, Melo RA, Barbosa AC, de Assis Morais MO. Risk factors for temporomandibular disorder: binary logistic regression analysis. Med Oral Patol Oral Cir Bucal. 2014;19(3):e232-6. (supports normal ROM values)
  21. ↑ Kalamir A, Pollard H, Vitiello AL, Bonello R. TMD and the problem of bruxism: a review. Journal of Bodywork and Movement Therapies. 2007;11(3):183-193.
  22. ↑ Gil-Martinez A et al. Management of pain in patients with TMD: challenges and solutions. J Pain Res. 2018;11:571-587.
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