The TMJ (temporomandibular joint) is a hinge joint that connects the jaw (mandible) to the skull bone above it (the temporal bone) on either side of the head. To understand how problems can affect the TMJ, it is important to know what a joint is and how joints operate.
A joint, also called an articulation, is the point at which two bones connect to each other. The joint is made up of a fibrous connective tissue and cartilage. Among their many functions, connective tissues provide structural support for other tissues, transport materials inside of the body, and store energy reserves.
Cartilage is also considered a connective tissue, but it is formed from gelatinous material and is made up of many fibers. Cartilage is inflexible and can endure significant pressure or tension. Cartilage has no nerves and no blood supply of its own.
The temporomandibular joint allows the jaw to move forward (protraction) and backwards (retraction), as when you move your bottom teeth in front of your top teeth and vice versa. This joint also allows what is called depression, or opening of the jaw, and elevation, or closing the jaw. When a person has TMJ disorder, they lose the natural flexibility of this joint, and all of these movements can become painful.