The non-specific theory in microbial etiology of inflammatory periodontal diseases

In the absence of toothbrushing, the gingival crevice is colonized by a complex indigenous microflora causing gingivitis, a non-specific inflammation. Subgingival plaque may develop by downgrowth into the inflamed pocket of those micro-organisms from supragingival plaque which can multiply there. By direct microscopy, increased proportions of motile rods and spirochetes have been found in diseased pockets. Cultures on selective media have demonstrated increased prevalence of various gram-negative rods. Cultures on non-selective media have revealed the complexity and variability of the subgingival microflora, comprising more than 200 species. Destructive periodontitis is the result of subgingival colonization, which is favored by such ecological changes as plaque accumulation, gingivitis, and gingival exudate. These changes increase the numbers of micro-organisms and alter their proportions, but no single species appears in active sites which is not also commonly present in inactive sites. The subgingival micro-organisms have several virulence factors which promote colonization of the pockets, destroy host defense mechanisms, and provoke inflammation. It appears that different combinations of indigenous bacteria, rather than just a single species, can produce the pathogenic potential necessary to cause progression from gingivitis to destructive periodontitis.