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INFLAMMATION. 143
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 de-
vitalized 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 re-
sulting 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 recupera-
tive 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 pro-
ducing periostitis, and which may occur on exposure to such
fumes after the extraction of teeth, manifests itself almost en-
tirely in the lower jaw.
Phosphorus-necrosis commences as inflammation of the peri-
osteum with the production of osteophytes, and results in nearly
total necrosis of the entire bone.