Actinomycosis is a specific inflammatory disorder infected by actinomycetes, oneof oral resident flora. Although actinomycosis frequently arises as gnathitis orperignathitis in the oral and maxillofacial region, it is rarely localized in the oral soft tissue. This report deseribes a rare case of actinomycosis in the buccal region. A 43-year-old man visited our hospital because of a soft mass in the left buccal region, which had gradually increased in size 2 weeks before admission. We clinically diagnosed the lesion as a fibroma or abscess of the left buccal region. Excision of the mass was performed, and antibiotics were given. Since various sizes of drusen were histopathologically observed in the specimens, the final diagnosis was actinomycosis. As for pathogenesis, actinomycetes seems to cause infection by decubital ulcers due to bite injuries. In addition to oral and dental hygienic guidance, adequate treatments for peripheral periodontitis, apical periodontitis, tooth malalignment, and tooth loss were performed.Then, the prognosis is good.
