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The mandible is the lower part of the jaw that moves. The jaw works as a hinge mechanism and has a network of mandibular muscles that help it to function properly. Primarily, the mandibular muscles on the sides of the jaw consist of masseter muscles, the temporalis muscles, and the pterygoid muscles. The muscles underneath the mandible include the digastrics, the geniohyoid, and the mylohyoid.
The masseters are mandibular muscles that function to close the lower jaw. There is a masseter muscle located on either side of the jaw. Aside from functioning to close the lower jaw, these muscles assist with chewing and grinding motions. They also function to retract the jaw, pulling it back when needed. Due to the fact that these muscles are so intricately involved in the grinding motion of the jaw, they can easily become tender and inflamed in individuals who have difficulty with conditions such as bruxism, where a person excessively grinds or clenches his or her teeth.
Along the sides of the face, two broad muscles extend from the sides of the jaw to the temple region. These mandibular muscles, called the temporalis muscles, have the shape of a semicircle and take up a good deal of space on the sides of the head. The temporalis muscles function with the masseter muscles to close the lower jaw and pull the jaw back. They also help with the crushing and grinding of food. As a result of the location of these muscles along the sides of the head, when a person experiences jaw pain or inadvertently eats something that is unusually hard or crunchy, he or she might experience headache-type pain as well.
Next to the masseter muscles, along the sides of the cheeks, the pterygoid muscles can be found. These muscles are split into the lateral pterygoids and the medial pterygoids. The lateral pterygoids serve to open the jaw, while the medial pterygoids work along with the masseter and the temporalis mandibular muscles to close the jaw. These particular muscles also assist with the side-to-side motion of the jaw. The pterygoid muscles are attached from the jaw to a point close to the eye sockets, so consequently, if one of these muscles becomes injured or inflamed, a person might experience eye pain in addition to jaw pain.
There are other mandibular muscles located under the chin. The geniohyoid and mylohyoid muscles function to open the lower the jaw. The digastric muscles, also found under the chin, are divided into anterior digastric and posterior digastric. Both of these muscles serve to lift the mandible when necessary. The position of the jaw and other muscles determine which of the digastric muscles will act to lift the mandible.