Lower Jaw (Mandible)

The lower jaw bears the lower dentition, but also provides support for the muscles of the floor of the mouth, and for the tongue. The lower jaw has the shape of a central arch with two arms, and is built from two bones that are connected at the center of the chin.

The lower jaw forms the temporomandibular joint with the temporal bone above it, by way of its two arms connecting to the bones of the face in a system of muscles and ligaments. Defects of the lower jaw are usually partial, but may involve proximal structures, such as the tongue and the floor of the mouth, the lips, and the cheeks. Defects of these types are common after the removal of benign or malignant tumors, though trauma and birth defects may also require partial reconstruction of the lower jaw.

Partial reconstruction of the lower jaw is the most common reconstruction performed on this bone. Partial reconstruction is made possible by using a metal plate when the defect is located on the side of the body of the lower jaw, or on the arm of the jaw. This type of reconstruction is relatively inferior, as the durability of the metal is limited to two or three years, and it is not uncommon for cracks to appear even before then, depending upon the stress to which it is exposed. This type of reconstruction is generally performed on people who are not suited to undergoing a complex reconstruction, performed by transferring bone together with its blood supply. Reconstruction with a metal plate is not carried out when the defect is in the center of the lower jaw, as the plate may burst out after a short period of time due to the high pressure it tends to place on the soft tissues covering it.

The optimum partial reconstruction is performed by transferring bone with the blood vessels supplying it, which are then reconnected to recipient blood vessels in the neck to reconstitute the blood supply, using microsurgical techniques. The bone most commonly used for this purpose is the fibula, taken from the shin, which permits reconstruction of up to half of the lower jaw, or even a little more. The fibula is completely harvested, except for its upper end, close to the knee, and its lower end, which forms the ankle joint. Both muscle and skin can be transferred with the bone in order to cover a defect of external skin or mucous membrane in the oral cavity, or to reconstruct part of the tongue. The advantage of the fibula is that it makes it possible to reconstruct the dentition at a later date, and, in some circumstances, even at the time of the removal of the lower jaw. In most cases, there is no residual loss of function of the fibula, and scarring is the only evidence that the bone has been harvested.

Additional sources of bone flaps used to partially reconstruct the lower jaw are the iliac from the pelvis, or the scapula from the shoulder. A flap from the iliac can supply a large piece of bone for reconstruction, but the thickness of the bone is usually not sufficient to permit the implantation of teeth. Flaps from the scapula are more limited in the quantity of bone that can be removed, and are sufficient only for a small or medium-sized defect.

Dr. Aharon Amir: Lower Jaw

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