Understanding temporomandibular disorders.

• Author: Moses, Allen J.

TEMPOROMANDIBULAR disorder (TMD) manifests itself in a variety of symptoms and clinical presentations. The basis of these illnesses is a spectrum of physical disorders capable of causing an abnormality or imbalance in the delicate working relationship of the mandible (lower jaw), the temporomandibular joints, the skull and the masticatory or chewing muscles. An explanation of the complexities of temporomandibular joint function and dysfunction will help simplify the approaches and analyses of defense counsel who are confronted with ever-increasing numbers of TMJ cases.(1)

The term TMJ refers to the temporomandibular joints. They are located in front of the ears and are the means by which the mandible or lower jaw attaches to the head. In animals, the jaw joint moves entirely as a hinge. In human beings, the TMJ is an extremely complex joint. It is the only joint connected across the midline of the body, and whose movement is limited by the presence of teeth. It is not a pressure bearing joint. It slides, it rotates, it allows the mandible to open and close, move side to side, forward, backward, and combinations of all these movements.

Understanding the Sounds

Paramount to an understanding of dysfunction is an explanation of TMJ sounds. Between the skull and condyle is a fibrocartilage disk. The disk ideally moves in coordination with the condyle to prevent bone rubbing against bone and serves as a lubricator and shock absorber, resulting in jaw movement that is smooth, silent and as friction-free as possible.

Trauma or malfunction of the TM mechanism causing a condyle to move on and off the disk in jaw movement is evidenced by a clicking sound and is referred to as disk displacement with reduction. Disk displacement also can occur without reduction, and in this situation, sometimes referred to as clinical closed lock, the affected condyle functions off the disk entirely. This condition is accompanied by limited range, irregular jaw movement and absence of a clicking sound.

Crepitus is a grating, grinding type of noise that can occur in the TMJ. It is the result of degenerative changes in the joint and commonly results from joint compression wearing the disk thin, possibly to the extent of perforation. It has a greater component of high frequency sounds than clicking, and the sound tends to be of longer duration.

A Kinetic Chain

Just like the song says, "The jaw bone's connected to the head bone, the head bone's connected to the neck bone." Human beings are indeed a kinetic chain. Holding the head upright has been likened to balancing a bowling ball on a broomstick.

Mandibular movement is involved in...