Necrosis signifies the death of bone-tissue, and corresponds to gangrene of soft parts. The degree of injury, traumatic or idiopathic, which is required to cause necrosis, is much less than that necessary to cause death of the soft tissues. This is due to the fact that the external (superficial) layers of bone receive their supply of blood from numerous small vessels given off" from the periosteum, and the separation of the periosteum from the bone, which sometimes occurs from the pus of an alveolar abscess making its way between the bone and the periosteum, deprives the external layer of bone of its blood-supply and causes necrosis. The occurrence of stasis resulting from the Haversian vessels of bone becoming obstructed owing to the presence of inflammatory stimulus which demands a larger blood-current and more blood-cells, and which these vessels cannot supply, on account of their inability to enlarge, is another reason for the susceptibility of bone to necrosis.

The devitalized portion of bone is called a "sequestrum," and the devitalized soft tissue is called a "slough." Necrosis may involve a small portion of a bone, or it may affect the entire bone.

The dead portion of bone becomes detached from the living tissues by the formation of granulation tissue between the devitalized and living portions, and finally the disintegration of this tissue separates the dead portion. Pus is always present, and around the necrosed bone, there is an accumulation of a fetid, purulent fluid, which contains broken-down tissue and debris resulting from decomposition as well as from the inflammatory process; the purulent fluid penetrates the tissues and reaches the surface.

The necrosed portion is lighter than living bone, on account of the organic portion having been removed by decomposition and the action of the granulation tissues.

Necrosis of bone is caused by impaired or arrested blood-supply, which may result from injury, inflammatory conditions induced by mercurial ptyalism, syphilis, phosphorous poisoning, extensive inflammation of neighboring parts, or any cause which impairs the vitality of the tissues. Fractures and inflammation of the periosteum (periostitis) are the most frequent causes of necrosis.

Necrosis of the jaws is much more common to the lower than to the upper jaw, which is, no doubt, owing to the greater nutrition of the upper jaw which not only renders it less liable to injury resulting in periostitis, but also increases its recuperative powers. The toxic forms of necrosis are due mainly to mercury, phosphorus, and arsenic.

The form known as "phosphor-necrosis" due to the vapor of phosphorus coming in contact with the periosteum and producing periostitis, and which may occur on exposure to such fumes after the extraction of teeth, manifests itself almost entirely in the lower jaw.

Phosphorus-necrosis commences as inflammation of the periosteum with the production of osteophytes, and results in nearly total necrosis of the entire bone.

Necrosis of the jaws may be either partial or complete - partial when it is confined to the aveolar process, complete when the entire thickness of the bone is affected. The causes are the same as those of periostitis, such as injuries, eruptive fevers, syphilis, periodontitis, scorbutus, mercurial, phosphorus, and arsenical poisoning, and ulceration of the soft tissues. The symptoms of necrosis are in the beginning the same as those of periostitis or periodontitis, and after the disease is established, the pus escapes by the side of the loosened teeth and the gums become detached from the bone, and pus finds an outlet from between them. In necrosis of the lower jaw the pus frequently penetrates the tissues covering the bone and points upon the under surface of the jaw; at other times the pus may follow the intermuscular connective tissue of the neck, and point as low down as the clavicle or breast. The necrosis may also extend to bones of the face and head. The necrosed portion of bone becomes a foreign body which the surrounding tissues endeavor to extrude, or to wall off and surround, owing to the presence of granulation tissue, which gradually perforates the surrounding bone at places of least resistance, the result being the formation of one or more sinuses, through which the dead portion can be withdrawn with little trouble. Separation finally takes place between the living and dead portions of the bone. While this is taking place, a quantity of new bone, especially in the case of necrosis of the lower jaw, is forming around the sequestrum; the new osseous tissue is called the "involucrum," which it is necessary to at least partially remove before the sequestrum can be withdrawn.

Treatment

The treatment of necrosis of bone consists in the removal of the dead portion (sequestrum), and the restoration of the parts to a condition favoring regeneration. The removal of the sequestrum or dead portion is accomplished with bone-forceps and chisels, and all the lining material of the cavities which the fragments have occupied should be scraped away with a sharp spoon. The cavities are then packed with iodoform gauze soaked in a mixture of balsam of Peru, containing ten per cent. of guiacol. Before the sequestrum or dead fragments separate from the living bone, no attempt should be made to remove them, but the suppurating surfaces should be frequently irrigated with antiseptic solutions. The fetid odor of the breath may be corrected by freely using a solution of permanganate of potassium and cinnamon: also the fetid odor of the discharges. The treatment of phosphorus-necrosis and other toxic forms, consists in the use of antiseptic solutions, the opening of abscesses, and the removal of diseased bone, and especially of dead bone upon the first provocation. The constitutional treatment in all forms of necrosis should be supporting, and liquid foods given where there is inability to open the mouth. Such tonics as iron, quinine, cod-liver oil, malt extracts are indicated, together with change of air.