Temporomandibular joints
(from Wikipedia.com)
This is arguably the most complex set of joints in the human body. Unlike typical finger or vertebral junctions, each TMJ actually has two joints which allow it to both rotate and to translate (slide). With use it is common to see wear of both the bone and cartilage components of it. Clicking is common as are popping motions and deviations in the movements of the joint. It is considered a TMJ disorder when pain is involved.
In a healthy joint, the surfaces in contact with one another (bone and cartilage) do not have any receptors to transmit the feeling of pain. The pain therefore originates from one of the surrounding soft tissues. When receptors from one of these areas are triggered, the pain causes a reflex to limit the mandible's movement. Furthermore, inflammation of the joints can cause constant pain, even without movement of the jaw.
Due to close proximity of the ear to the temporomandibular joint, TMJ pain can often be confused with ear pain. The pain may be referred in around half of all patients and experienced as otalgia (earache). Conversely, TMD is an important possible cause of secondary otalgia Treatment of TMD may then significantly reduce symptoms of otalgia and tinnitus , as well as atypical facial pain. Despite some of these findings, there are some researchers who question whether TMD therapy can reduce symptoms in the ear, and currently a debate is ongoing to settle the controversy.
The dysfunction involved is most often in regards to the relationship between the condyle of the mandible and the disc. The sounds produced by this dysfunction is usually described as a "click" or a "pop" when a single sound is heard. When there are multiple, rough sounds, it is described as "crepitation" or "crepitus".