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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).
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 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 ).
Ask the patient to open and close whilst placing two fingers over the space of the TMJ. Opening of less than 35mm in the mandible is considered to be restricted and such restriction may be associated with intra-capsular changes within the joint. [28] Following this, ask the patient to move their jaw to the right and following this, to the left.
B. X-ray, MRI or bone scintigraphy demonstrate TMJ disorder; C. Evidence that pain can be attributed to the TMJ disorder, based on at least one of the following: pain is precipitated by jaw movements or chewing of hard or tough food; reduced range of or irregular jaw opening; noise from one or both TMJs during jaw movements
It is bordered below by a number of splenial bones, while the angle of the jaw is formed by a lower angular bone and a suprangular bone just above it. The inner surface of the jaw is lined by a prearticular bone, while the articular bone forms the articulation with the skull proper. A set of three narrow coronoid bones lie above the ...
The jaw in tetrapods is substantially simplified compared to fish. Most of the upper jaw bones (premaxilla, maxilla, jugal, quadratojugal, and quadrate) have been fused to the braincase, while the lower jaw bones (dentary, splenial, angular, surangular, and articular) have been fused together into a unit called the mandible. The jaw articulates ...
The upper joint compartment formed by the articular disc and the temporal bone is involved in translational movement—this is the secondary gliding motion of the jaw as it is opened widely. [ 2 ] In some cases of anterior disc displacement, the pain felt during movement of the mandible is due to the condyle compressing this area against the ...