The temporomandibular joint (TMJ) is a diarthrodial joint that connects the mandible (lower jaw) to the temporal bone at the side of a skull. As a modified hinge joint, not only does the TMJ enable the jaw to open and close, it also enables the jaw to move forward and backward, as well as laterally.
This is a ginglymo-arthrodial joint; the parts entering into its formation on either side are: the anterior part of the mandibular fossa of the temporal bone and the articular tubercle above; and the condyle of the mandible below.
Classification of disorders involving the temporomandibular joint involve six categories:
- Disorders can be described as functional disturbances, which is also called temporomandibular joint disorder (TMJD), myofacial pain dysfunction syndrome (MPDS), TMJ pain dysfunction syndrome, or mandibular dysfunction. This disorder is marked by an acute or chronic inflammation of the temporomandibular joint.
- Disorders of the temporomandibular joint can manifest as organic disease entities. These include osteoarthritis, rheumatoid arthritis, psoriatic arthritis, and infectious arthritis.
- There can be ankylosis (”fusion”) of various structures of the joint. Subcategories of ankylosis include fibrous and bony ankylosis.
- Trauma to the temporomandibular joint can result in fractures or non-fractures.
- Disorders can result from the condylar head of the mandible being trapped anterior to its correct location and thus are referred to as dislocations. A dislocation may be chronic or acute.
- Disorders of the temporomandibular joint may include tumors, though this occurs very rarely. Tumors may express in the form of osteomas, ostochondromas, soft tissue invasions, or metastasis from a different tumor in the body.
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