Investigation of infectious organisms causing pericoronitis of the mandibular third molar

The purpose of the study was to identify the most frequently encountered pyogenic organisms involved in pericoronitis to permit more targeted antibiotic therapy. Pericoronal pockets of mandibular third molars from 37 patients showing symptoms of acute, severe pericoronitis were sampled and subjected to microbiologic analysis, including primary evaluation by phase-contrast microscopy. To avoid overgrowth with faster-growing, less fastidious organisms, specimens were cultured on a wide variety of selective media (supporting growth of fastidious bacteria, protozoa, and fungi). Microscopic examination indicated spirochetes in 55% and fusiform bacteria in 84% of the samples. A total of 441 microorganisms were isolated and identified from the 37 cultured samples. Besides obligate anaerobic bacteria, including various Actinomyces and Prevotella species, a predominantly facultative anaerobic microflora was cultivated, that is, Streptococcus milleri group (78% of samples), Stomatococcus mucilaginosus (71%), and Rothia dentocariosa (57%). It was concluded that the Streptococci milleri group bacteria, well-known for their ability to cause suppurative infections, are most likely involved in the pathogenesis of acute severe pericoronitis of the lower third molar.