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In humans, the mandible, or lower jaw, is connected to the temporal bone of the skull via the temporomandibular joint. This is an extremely complex joint which permits movement in all planes. The muscles of mastication originate on the skull and insert into the mandible, thereby allowing for jaw movements during contraction.
The digastric muscle (also digastricus) (named digastric as it has two 'bellies') is a bilaterally paired suprahyoid muscle located under the jaw.Its posterior belly is attached to the mastoid notch of temporal bone, and its anterior belly is attached to the digastric fossa of mandible; the two bellies are united by an intermediate tendon which is held in a loop that attaches to the hyoid bone.
The mylohyoid muscle elevates the hyoid bone and the tongue. This is particularly important during swallowing and speaking. Alternatively, if other muscles are used to keep the position of the hyoid bone fixed, then the mylohyoid muscle depresses the mandible. [1] It also functions as reinforcing the floor of mouth. [1]
These four muscles have different actions, but in general assist in elevating the hyoid bone and widening the esophagus during swallowing.When the two bellies of the digastric contract, they pull upward on the hyoid bone; but if the hyoid is fixed from below, the digastric assists in extreme opening of the mouth such as yawning or taking a large bite of an apple. [1]
Retrain oral, lingual, and facial muscles to facilitate correct resting posture of tongue, lips, and jaw; Establish mature swallowing patterns; Prevent relapses after orthodontic treatment; Improve the relationship between dental arches; reduce open bite and overjet; Maintain overall facial muscle tone needed for chewing, swallowing, and speech
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.
Pain and tenderness on palpation in the muscles of mastication, or of the joint itself (preauricular pain – pain felt just in front of the ear). Pain is the defining feature of TMD and is usually aggravated by manipulation or function, [ 2 ] such as when chewing, clenching, [ 12 ] or yawning, and is often worse upon waking.
The facial muscles are just under the skin (subcutaneous) muscles that control facial expression. They generally originate from the surface of the skull bone (rarely the fascia), and insert on the skin of the face. When they contract, the skin moves. These muscles also cause wrinkles at right angles to the muscles’ action line. [2]