The Jaw
It is hard to believe that a backache or a pain in the legs can originate in the jaw. However, an understanding of the relationship between the muscles and bones in the jaw and the rest of the body leads to an understanding of how an imbalance in one part affects another.

The jaw bears the teeth and forms the framework of the mouth. It consists of two bones: the maxilla (upper jaw) and mandible (lower jaw). The upper part of the jaw is stationary, while the lower part is the only movable bone in the face. The position of the jaws is dependent on the relationship of the teeth to each other when the mouth is closed.

The mandible or the lower part of the jaw functions like a hinge, permitting the mouth to open and close, as shown in Figure 1.1. This hinge action is accomplished by bones and muscles located in the skull, neck, and face. There are two phases involved in opening and closing the jaw. The first phase is a simple hinge action. The second phase involves a gliding action of the joint, which helps open the jaw to its maximum. The muscles that coordinate the movements of the jaw joints originate in the head, neck, and face areas. Due to the relationship of these muscles to the muscles of the shoulder and back, any imbalance in the jaw area may eventually affect the shoulder and back.

The temporal bone of the skull (the bone on the side of the head, above the ears), and the mandible fit together to form the jaw joint called the temporomandibular joint as shown in Figure 1.2. There are two such joints-one on the left side of the head and one on the right side.

Figure 1-2. Temporal Bone and Mandible Form the Temporomandibular Joint

Figure 1.3 shows the components of the temporomandibular joint. Each joint is surrounded by a saclike sheath called a capsule.This capsule contains synovial fluid, which lubricates and nourishes the joints. At each end of the lower jaw, there is a knoblike structure called a condyle. At the ends of bones throughout the body, condyles are attached to muscles that join the bone to nearby bones. Mounted on top of each condyle is a cushion made of cartilage and known as the disc. As with any joint in the body, a disc or cushion sits between the joint and its socket, which, in the case of the jaw, is located on the skull. This disc moves with the condyle and prevents it from hitting the temporal bone. When the disc is abnormally placed, the jaw may not function properly causing pain or discomfort in the head, neck, shoulder, and back area. Since the jaw joint sits right in front of the ear, any problems with this joint area may also affect the ears, eyes, and sinuses.