The pathologic alterations occurring in the gingival tissues of humans immediately following the beginning of plaque accumulation have not been elucidated previously. Seven males, 22–31 years of age, free of clinical manifestations of dental and periodontal disease, and exhibiting a Plaque Index score of zero for the previous 28 days served as subjects. Plaque control measures were discontinued for 8 days and biopsies, were taken from the buccal marginal gingiva of the first premolars on days 0, 2, 4, and 8. Paraffin‐ and Eponembedded sections, treated with a variety of histochemical stains were analyzed microscopically and cell counts were done on 1‐micron Epon sections. At 2 and 4 days following the beginning of plaque accumulation, the vessels subjacent to the junctional epithelium exhibited vasculitis and alterations in the perivascular collagen. There was a statistically significant increase in the number of neutrophils residing in the junctional epithelium. By the end of the 8‐day period, the number of small mononuclear cells, mostly lymphocytes, in the connective tissues had increased by 3‐fold and the area of collagen fiber alteration by 4‐fold. In addition, the number of fibroblasts per unit area of connective tissue decreased significantly. Thus, within the period of 8 days following the beginning of plaque accumulation, anearlylesion exhibiting many features characteristic of delayed hypersensitivi
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