Over 10 million people in the USA suffer from TMJ or temporomandibular joint syndrome, a condition in which the temporomandibular joint does not function correctly, which usually generates pain of varying degrees.

The temporomandibular joint connects the temporal bone, which is the bone that forms the sides of the skull with the jawbone. The condition of TMJ produces pain in the muscles and joints of the jaw that frequently radiate to the ear, face, head, neck, and shoulder. 

“TMJ” stands for TemporoMandibular Joint, and “TMD” stands for TemporoMandibular Dysfunction of the jaw joint. Sometimes TMJ disorders are abbreviated TMD.
There  are two TMJs, one in front of each ear, connecting  the lower jaw-bone (the mandible) to the skull (temporal bone). The joint allows the jaw to move up and down, side-to-side, and forward and backward, providing all the mobility necessary for biting, chewing and swallowing food, for speaking, and for making facial expressions. Between the top end of the jaw (condyle) and the socket in the skull is a disk of cartilage, which – like the discs in the neck and back – serve as shock absorbers, protecting the bones from hitting each other.

Sometimes TMJ can lead to problems that don't seem related to your jaw. Pain in the TMJ can interfere with everyday activities. Symptoms that can originate from dysfunction in your jaw joints include headaches, difficulty swallowing, stress, earaches, chronic ear-infections, and neck, shoulder, and back pain.

It is by far the most complex and most over-worked joint in the human body.