Anatomy of the Jaw
In regards to jaw anatomy, the major joint in the jaw is the temporomandibular joint (TMJ) which connects the lower jaw to the skull (temporal bone) under the ear. Some physicians associate disorder in this joint with tiny myofascial trigger points, or contractions (knots), in the overworked or traumatized jaw muscles. Temporomandibular joint disorder (TMJ) has been associated with jaw pain itself, as well as numerous seemingly unrelated issues such as sinus problems, problems in the eyes, such as eyelids twitching or drooping, toothache, and inner-ear itch.
The temporomandibular joint includes muscles, blood vessels, nerves, and bones, with one TMJ on either side of the jaw. The muscles in the jaw control rotation and hinge movement allowing for chewing, talking, and yawning. Muscles in the face also control chewing (mastication). By placing a finger in front of the ear on either side of the face and opening the mouth it is possible to feel the rounded ends of the lower jaw (the condyles) sliding along the socket of the joint. There is a soft disc between the condyle and the temporal bone that is there to keep the action smooth and absorb and distribute shock from movements such as chewing. The degeneration of this disc can cause problems, just as degeneration of intervertebral discs can lead to pain, numbness, and weakness. MRI scans can detect alterations in the disc of the TMJ.
Specific muscles in the jaw antomy include the temporalis which extends across the side of the head in a fan-like fashion to connect to the lower jaw. Problems with the temporalis can cause pain similar to migraines, which means that the underlying cause is left untreated. The other masticating muscle is the masseter which closes the jaw and also stretches from the temporal bone to the mandible. The disc in the temporomandibular joint is attached to the lateral pterygoid which is the muscle that opens the jaw by pulling the condyle forwards. This attachment to the disc can make this muscle very painful as disc degeneration occurs. The last of the four major jaw muscles is the internal pterygoid which sits very close to the trigeminal nerve as it passes through the jaw and is also responsible for closing the mouth. This proximity to a major nerve is the reason why intense nerve pain often results from muscle pain in the jaw.
Buccinator and Platysma Muscles
Other facial muscles within the jaw antomy, more responsible for facial expression than jaw movement, but occasionally involved in the pathology of TMD include the buccinator which is the muscle that flattens the cheek against the teeth. The buccinator originates from the mandible and stretches to the skin around the mouth. The zygomaticus muscle raises the corner of the mouth, having originated from the zygomatic bone also known as the cheekbone. Another muscle associated with the jaw muscles is the platysma which moves the mouth downwards and stretched from the chest to the lower part of the mandible.
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