Mandibular condyle

The lower jawbone (mandible) forms a U shape beneath the mouth, with both rear ends extending upward. The rounded projection at the very top and back of this raised portion of bone is the mandibular condyle. It is roughly an elongated oval in shape, with a smooth articular surface. Its surface is covered with fibrocartilaginous tissue, which reduces friction as the joint moves. During the growing years, this area also serves as a key site guiding the development and growth of the entire mandible.

The mandibular condyle fits into the articular fossa, a hollow on the side of the skull in the temporal bone, to form the temporomandibular joint. Between the two bones lies a cushion-shaped articular disc, which absorbs impact and helps the bones glide smoothly without directly striking each other. Another important role of this disc is to distribute the chewing loads evenly.

Mouth opening occurs naturally in two stages.

1. Rotation: When you first open your mouth slightly, the condyle rolls as though rotating in place within the articular fossa. This stage mainly covers opening to about one or two finger-widths. 2. Translation: As you open wider, the condyle continues to roll while sliding forward along the front slope of the articular fossa (mandibular translation). At the same time, the articular disc moves forward with it, remaining wrapped around the head of the condyle.

When you close your mouth, this process happens in reverse, returning the structures to their original positions. Rotation and translation must work together to provide a sufficient opening range of around three finger-widths (mouth opening range of motion). The mandibular condyle and articular disc moving together in a consistent rhythm is the foundation of comfortable jaw function.

Place your fingers lightly just in front of your ear, then slowly open and close your mouth. As you open, you will feel something slide forward beneath your fingertips. This is the movement of the mandibular condyle. You use this joint movement when yawning, biting into a large piece of food, and singing.

The two mandibular condyles are firmly connected by a single lower jawbone, so when one joint moves, the other responds as well. If you habitually chew on only one side or spend prolonged periods clenching your teeth, the joints may bear uneven loads, and the muscles around one side of the jaw may feel more sore and tight.

If the timing of movement between the condyle and the articular disc is slightly out of sync, you may hear a click in your jaw or feel a catch while opening your mouth. Joint sounds alone are common in everyday life and often are not a major cause for concern if there is no pain. For details, see Temporomandibular joint sounds and Joint crepitus. For an explanation of changes in disc position, see Anterior disc displacement of the temporomandibular joint.

• Avoid opening your mouth excessively wide. Lightly supporting the underside of your jaw with your hand when yawning or eating bulky foods helps prevent the condyle from moving too far forward.
• Regularly check whether you are clenching your teeth. Keeping your lips gently closed and your upper and lower teeth slightly apart, without touching, is the most comfortable resting position for the temporomandibular joint. See also Tooth clenching and Bruxism.
• Try to develop the habit of alternating sides when chewing. This reduces the concentration of load on a particular part of the joint.
• Cut hard or tough foods into small pieces. On days when you need to chew for a long time, allow plenty of rest so your jaw muscles (muscles of mastication) can release tension.
• Try to spend less time resting your chin or one cheek on your hand. These positions place sustained, uneven pressure on one temporomandibular joint.
• Applying a warm, moist compress around the jaw to ease tension, followed by gentle joint movements such as slowly opening and closing your mouth, can help relax the surrounding tissues. For more detailed care guidelines, see Temporomandibular disorder self-management.

You have noticeable temporomandibular joint pain when opening your mouth, or you have difficulty opening it. Your jaw gets stuck in an open position and you cannot close it (temporomandibular joint dislocation). Jaw sounds become progressively louder or start to be accompanied by pain. If these signs recur, it is a good idea to have your condition assessed by a professional who can thoroughly evaluate temporomandibular disorders.