Bacteriology of Human Experimental Gingivitis: Effect of Plaque Age

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Abstract
Subjects [25] with previously excellent hygiene and healthy gingiva developed heavy plaque accumulations and bleeding or nonbleeding gingivitis about certain papilla after 21 days of no oral hygiene. Gingival marginal plaque about a single papilla was collected at 0, 1, 2 and 3 wk of no oral hygiene in each subject. The plaque was dispersed, serially diluted and plated on MM10 sucrose agar in an O2-free atmosphere. From 50-100 colonies from a single high-dilution plate were characterized for each sample. Over 8500 isolates were partially characterized and placed into 1 of 29 taxonomic species or groups. The flora was predominantly gram-positive at all time periods. Streptococcal species dominated in 0 and 1 wk old plaques, i.e., 62 and 43% of the colony-forming units (CFU), but dropped to 26-32% of the CFU in the 2 and 3 wk old plaques. Actinomyces spp. dominated in older plaques, i.e., 40-50% of the CFU. A. israelii was the most prominent species in the older plaques. Veillonella accounted for 15-20% of the CFU at all time periods. Although the other gram-negative species increased with time, collectively they averaged less than 5% of the CFU at 3 wk. The shift from a Streptococcus-dominated plaque to an Actinomyces dominated plaque was the most striking microbial change observed as plaque aged.