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The four classical muscles of mastication elevate the mandible (closing the jaw) and move it forward/backward and laterally, facilitating biting and chewing. Other muscles are responsible for opening the jaw, namely the geniohyoid , mylohyoid , and digastric muscles (the lateral pterygoid may play a role).
Trismus is a condition of restricted opening of the mouth. [1] [2] The term was initially used in the setting of tetanus. [2]Trismus may be caused by spasm of the muscles of mastication or a variety of other causes. [3]
Contraction of the lateral pterygoid acts to pull the disc and condyle forward within the glenoid fossa and down the articular eminence; thus, the action of this muscle serves to protrude the jaw, it with the assistance of gravity, and the digastricus muscle also opens the jaw. The other three muscles close the mouth; the masseter and the ...
The action of the muscle during bilateral contraction of the entire muscle is to elevate the mandible, raising the lower jaw. Elevation of the mandible occurs during the closing of the jaws. The masseter parallels the medial pterygoid muscle, but it is stronger and superficial fibres can cause protrusion.
Sometimes TMD pain can radiate or be referred from its cause (i.e. the TMJ or the muscles of mastication) and be felt as headaches, earache or toothache. [12] Due to the proximity of the ear to the temporomandibular joint, TMJ pain can often be confused with ear pain. [23]
The temporalis muscle is covered by the temporal fascia, also known as the temporal aponeurosis. This fascia is commonly used in tympanoplasty, or surgical reconstruction of the eardrum. The temporalis muscle is accessible on the temples, and can be seen and felt contracting while the jaw is clenching and unclenching.
The jaw elevator muscles develop the main forces used in mastication. The force generated during routine mastication of food such as carrots or meat is about 70 to 150 newtons (16 to 34 lbf ). The maximum masticatory force in some people may reach up to 500 to 700 newtons (110 to 160 lbf ).
A concerted effort of the lateral pterygoid muscles helps in lowering the mandible and opening the jaw. Unilateral action of a lateral pterygoid muscle causes contralateral excursion (a form of mastication), usually performed in concert with the medial pterygoids. [citation needed] When they work independently, they can move the mandible side ...