The muscles of Mastication are an integral part of the body. They play a major role in digestion, help in maintaining our teeth inside of our mouth, and play a major role in our airway development.
Muscles Of Mastication
The muscles of mastication play an important role in jaw movements, and are innervated by the mandibular nerve which is a branch from the trigeminal nerve or cranial nerve V.
There are four paired muscles of mastication, with each having their own unique function, and they include:
- Medial pterygoid
- Lateral pterygoid
The temporalis muscle originates in the temporal fossa and inserts into the coronoid process of the mandible. It also helps to elevate the jaw, by closing the mouth; and it helps to retract the mandible, by pulling the jaw backwards.
The Temporalis And Pain
Oftentimes this broad, fan-shaped muscle can be a major contributing factor to what we know as tension headaches, due to its location on the sides of the head. This muscle contracts when you clench and unclench your jaw. Therefore if you have the tendency of clenching your teeth together, tend to bite your nails, or like to chew on pens to name a few, this muscle’s tendon can become inflamed and contribute to pain in the associated area. A study conducted on “Muscle fatigue in the temporal and masseter muscles in patients with temporomandibular dysfunction” concluded that individuals who tend to clench their teeth, and/or have a TMJ disorder, tend to have fatigue present in their chewing muscles. (1) Fatigue, due to over use of this muscle or any type of injury to it will not just lead to headaches, but may also lead to radiating pain to the nearby areas. Areas that may be affected can include: the jaw, ear, shoulder, and skull.
The masseter muscle is a rectangular-shaped muscle of Mastication, that is one of the strongest and most superficial muscles of mastication. It aids in elevating the jaw, or closing of the jaw; and It is made up of two heads:
- Superficial head: the superficial head of the masseter originates in the zygomatic process of the maxilla and from the anterior two-thirds of the inferior border of the zygomatic arch; inserting into the angle of the mandible. (2)
- Deep head: the deep head of the masseter muscle originates in the posterior one third and the entire medial surface of the zygomatic arch; inserting into the ramus of the mandible.(2)
Clenching and grinding of the teeth can lead to overdevelopment of this muscle. Over use of the masseter muscles can create changes in the craniofacial structures and lead to a square jaw line. In addition to esthetics changes, overdevelopment of this muscle can also contribute to myofascial pain, trismus (lockjaw), and facial asymmetry to name a few.
The medial pterygoid is the deepest muscle of mastication. It is rectangular in shape, and is made up of two heads:
- Deep head- “The deep head is the larger of the two heads, and it originates from the pterygoid fossa on the medial surface of the lateral pterygoid plate of the sphenoid bone. (2)
- Superficial head- The smaller superficial head originates from the lateral surfaces of both the pyramidal process of the palatine bone and maxillary tuberosity of the maxilla.
Both heads then pass inferiorly, posteriorly, and laterally to insert on the medial surface of the mandibular ramus and angle of the mandible, as far superior as the mandibular foramen.” (2)
The medial pterygoid acts to elevate the mandible and helps the lateral pterygoid move the jaw from side to side, and it is innervated by the medial pterygoid nerve, which is a branch of the trigeminal nerve.
Medial Pterygoid and Dental Treatment Complications
The medial pterygoid muscle may become tense during dental treatment, as maintaining the jaw open for a long period of time can contribute to muscle fatigue. A study conducted on “Botulinum Toxin in the Treatment of Muscle Specific Oro-Facial Pain: A Literature Review”, stated that when examining patients who suffer from temporomandibular disorders (TMD or TMJ), a dental professional may discover that the medial pterygoid muscle, as well as the temporalis, and masseter muscles may be tender to the touch. (3)
“The lateral pterygoid muscle is a craniomandibular muscle that plays a crucial role in the craniofacial system. It is the key muscle of the inferior temporal region. The Lateral pterygoid muscle is active during mastication and during mandibular movements such as protrusion (forward movement of the mandible), abduction (depression of the mandible), mediotrusion (movement of the mandibular condyle towards the midline) and particularly during speaking, singing and clenching.” (4)
The lateral pterygoid is made up of two heads:
- Superior head- the superior head inserts into the anterior surface of the neck of the mandibular condyle at the pterygoid fovea of the mandibular as well as the temporomandibular joint disc and capsule (2)
- Inferior head- the inferior head inserts on the anterior surface of the neck of the mandibular condyle at the pterygoid fovea of the mandible (2)
Lateral Pterygoid and Pain
The lateral pterygoid muscle plays an important role in those suffering from temporomandibular disorders. Spasms seen in this muscle can be very painful and result in a lockjaw, which may require analgesics or muscle relaxants. “Clinical examination of patients with such disorders exhibits pain in the region of this muscle during jaw movements and during palpation behind the tuberosity region.”(4)
The muscles of mastication play a pivotal role in our craniofacial development, and can impact our quality of life if there is pain that is associated with them. Therefore, proper function is essential.
- Fehrenbach, Margaret J., and Susan W. Herring. Illustrated Anatomy of the Head and Neck. Elsevier, 2017.
- Sunil Dutt, C., Ramnani, P., Thakur, D., & Pandit, M. (2015). Botulinum toxin in the treatment of muscle specific Oro-facial pain: a literature review. Journal of maxillofacial and oral surgery, 14(2), 171–175. https://doi.org/10.1007/s12663-014-0641-9
- Rathee M, Jain P. Anatomy, Head and Neck, Lateral Pterygoid Muscle. [Updated 2020 Jan 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK549799/