Osteomyelitis

The mandible (lower jaw), due to decreased vascularity (blood supply & flow), is
involved 6 times more often than the maxilla (upper jaw).
The mandible has a relatively limited blood supply and dense bone with thick bony
(cortical) plates. Infection causes acute inflammation in the medullary (bone
marrow) soft tissues and inflammatory exudate (a fluid with a high content of
protein and cellular debris which has escaped from blood vessels and has been
deposited in tissues or on tissue surfaces, usually as a result of inflammation. It
may be septic or non-septic) spreads infection through the marrow spaces. It also
compresses blood vessels confined in the rigid boundaries of the vascular canals.

Thrombosis (the formation or presence of a thrombus [a clot of coagulated blood
attached at the site of its formation] in a blood vessel) and obstruction then lead to
further bone necrosis.

Dead bone is recognisable microscopically by lacunae (a cavity, space, or
depression, especially in a bone, containing cartilage or bone cells) empty of
osteocytes (a cell characteristic of mature bone tissue. It is derived from
osteoblasts and embedded in the calcified matrix of bone. Osteocytes are found in
small, round cavities called lacunae and have thin, cytoplasmic branches) but filled
with neutrophils (white blood cells) and colonies of bacteria which proliferate in the
dead tissue.

Pus, formed by liquefaction of necrotic soft tissue and inflammatory cells, is forced
along the medulla and eventually reaches the sub-periosteal region by resorption
(an organic process in which the substance of some differentiated structure that
has been produced by the body undergoes lysis and assimilation) of bone.
Distension of the periosteum by pus stimulates sub-periosteal bone formation but
perforation of the periosteum by pus and formation of sinuses on the skin or oral
mucosa are rarely seen now.

At the boundaries between infected and healthy tissue, osteoclasts (a specialised
bone cell that absorbs bone) resorb the periphery of the dead bone, which
eventually becomes separated as a sequestrum (a fragment of dead bone
separated from healthy bone as a result of injury or disease). Once infection starts
to localise, new bone forms around it, particularly sub-periosteally.

Where bone has died and been removed, healing is by granulation with formation of
coarse fibrous bone in the proliferating connective tissue. After resolution, fibrous
bone is gradually replaced by compact bone and remodelled to restore normal
bone tissue and structure (and function).

Piercing, deep and constant pain predominates in the clinical presentation in adults,
while low or moderate fever, cellulitis, lymphadenitis, or even trismus may also be
noted.

In the mandible, changes in sensation affecting the lower lip (paræsthesia or
dysæsthesia of the lower lip) may accompany the disease. When the disease
spreads to the peri-osteum (definition) and the surrounding soft tissues, a firm
painful œdema (definition) of the region is observed, while the tooth becomes loose
and there is discharge of pus from the periodontium. Radiographic examination
reveals osteolytic (definition) or radiolucent (definition) regions

Therapy entails combined surgical (incision, drainage, extraction of the tooth and
removal of sequestrum) and chemo-therapeutic treatment (with antibiotics).