Abstract
Only fragmentary knowledge is available concerning the morphology of subgingival plaque formation. The purpose of this study is to observe the sequential development of bacterial plaque on subgingival area by scanning electron microscopy.
Eight teeth in seven patients during treatment for chronic periodontitis were used in this study. These teeth with severe periodontal lesion, probeable to a depth of 6mm or more, would have to be extracted for periodontal reasons. A metal inlay into which dentin fragment had been inserted was fastened with temporary cement in a cavity prepared from gingival margin to subgingivally about 5mm. In order to observe plaque formation under the same conditions, a thorough root planing was carried out every time an inlay was set and the subjects were instructed to avoid as much as possible cleaning the tooth during the experimental periods. In this way, this inlay remained over and over in the same cavity for varying periods (from 1 day to 49 days). Forty specimens from eight teeth were observed by SEM.
The results were as follows;
1. The most apical border of subgingival plaque was distinguished from the dentin surface or the acquired pellicle. Until 21 days, the distance from the gingival margin to it was gradually increased, but afterwards its value was not changed.
2. The rate of plaque advance into subgingival area was in proportion to the amount of supragingival plaque particularly in early plaque development.
3. The leukocytes which seemed to be derived from periodontal pocket wall were predominantly observed on an area being 2-3mm from gingival margin. It was likely that leukocytes might have played an important role in host defense against plaque invasion.
4. As to the process of subgingival plaque formation, after supragingival plaque had been allowed to accumulate, subgingival plaque formation occurred. Namely, it seemed that the establishment of subgingival plaque followed the occurrence of apical growth into the pocket from supragingival plaque.
The experiment suggested that the formation of subgingival plaque is a slow process as compared with that of the supragingival plaque, and even after 49 days, the bacterial plaque invaded only one third of the pocket depth. It seemed that the subgingival plaque had to be formed under the constant exposure of host's defense mechanisms, for example, PMNLs.
