As the human lower jaw (mandibula) itself is a hard bone, and when bacterial inflammation occurs in it by pericoronal infection of the 3rd molar or apical infection of caries tooth, the inflammation remains in the bone marrow and often progresses to acute osteomyelitis. The prominent sign of acute osteomyelitis in the lower jaw is mental nerve palsy which is the so-called Vincent's Syndrome. The causative organisms are not different from those of the common odontogenic infections. Recently, we have identified some strains of Oral Streptococci tolerant against PCs and Cefems and also ones capable of biofilm formation. When antimicrobial agents or drainage proves unsuccessful, acute osteomyelitis may become chronic, which is more difficult to treat. Surgical procedures, such as, debridement or decortication of cortex bone are necessary in most cases. If these surgical procedures do not give satisfactory result, the amputation of the jaw is not rare.