Various structures in the jaw complex can affect the temporomandibular joint (TMJ) differently in TMJ disorders. Depending on the structures involved, pain, reduced mobility, and/or sounds may be produced by the TMJ.
Articular Disc of the TMJ
The articular disc of the TMJ is a flexible and elastic tissue that acts as a cushion between the bony surfaces of the jaw joint’s mandibular condyle and the temporal bone. This disc lacks blood vessels and nerves and does not have any sensation to pain. Anteriorly, the disc attaches to the lateral pterygoid muscle, and posteriorly, it continues as a retrodiscal tissue—loose connective tissue fully supplied by blood vessels and nerves.
A majority of TMJ disorders have a displaced articular disc of the temporomandibular joint, also called internal derangement of the TMJ.1 Displacement of the TMJ's articular disc is not a disease by itself, but a consequence to various disorders affecting the TMJ.
Internal derangement of the TMJ occurs in several stages that can be thought of as two general stages: early and latter stages. Although, the latter stages may not always develop.
- Anterior disc displacement with reduction. In the early stages, the articular disc moves forward, causing the retrodiscal tissue to be pulled in between the condyle and the temporal bone. Since the retrodiscal tissue is well innervated by nerves and blood vessels, this condition causes pain during jaw movements. A clicking sound is produced when the jaw opens and closes due to the condyle moving over the anteriorly displaced disc.
- Anterior disc displacement without reduction. In the latter stages, the condyle stays behind the anteriorly displaced disc, and no longer moves over the disc during jaw movements. This results in pain along with restricted mouth opening or locking. Locking is intermittent initially and may progress over time when the disc consistently does not reduce. As the anterior disc displacement worsens, the disc consistently stops reducing and the mouth opening may become less than 40mm between the edges of the upper and lower front teeth.2 This stage is associated with severe pain and grating sounds with or without degenerative bony changes.
Sometimes, internal derangement may be painless and have other symptoms, such as jaw sounds while opening and closing the mouth. In such cases, the condition may resolve on its own without any treatment.
Muscles of the TMJ
TMJ disorders may also result from acute muscle strain or chronic overuse or misuse of the jaw muscles. These muscles may become sore, tender, and/or swollen resulting in myofacial pain and dysfunction. TMJ muscle pain and other symptoms are typically felt in the face, jaws, teeth, and/or area in front of the ears. Pain from the TMJ muscles may also radiate to the head, neck, shoulders, and/or upper back.
Nerves of the TMJ
The mandibular nerve lies in close proximity to the TMJ and may cause neuropathic pain if compressed or irritated. A medially displaced articular disc may cause direct damage to the mandibular nerve or its branches by exerting compression or friction during a jaw-opening movement. Nerve pain from the TMJ complex may spread to other parts, such as the head, teeth, and/or ears through the trigeminal spinal nucleus of the brain stem.