Dark‐Field Microscopic Monitoring of Subgingival Bacteria During Periodontal Therapy

T he purpose of this study was to explore the application of microscopic evaluation of the sulcular flora to aid diagnosis and to evaluate progress of treatment during initial (presurgical) periodontal therapy. Fifteen adult patients with clinical diagnosis of moderate to severe periodontitis were used. Two contralateral healthy sulci and two contralateral periodontal pockets were chosen for examination in each patient. Clinical and microbiological assessments of these sites were made at four separate appointments, as follows: (1) at the inception of therapy, prior to plaque control instructions; (2) 2 weeks following plaque control instruction; (3) 2 weeks following supragingival scaling; and (4)4 weeks following root planing of diseased sites. Initial therapy was completed in 10 to 12 weeks. Clinical features monitored during the study were the Gingival Index, Plaque Index and gingival fluid flow. The bacterial examination consisted of dark‐field microscopic counting of morphologic forms and culturing of samples using a medium selective for Bacteroides species. Subgingival bacterial samples were obtained with a sterile curette from each site at each of the four appointments. The samples were placed immediately after procurement into anaerobic transport medium from which agar plate cultures were established. Microscopic counting was performed within 1 hour. One hundred microorganisms were evaluated in random microscopic fields and categorized on the basis of cell morphology and motility. Based on paired t tests, significant differences in subgingival flora were found when healthy sites were compared with diseased sites at the inception and completion of the experimental period. Significant changes were also found in intragroup samples, both healthy and diseased, between the beginning and end of initial therapy. Coccoid cells dominated the healthy sites at the initial appointment (62.3% vs. 18.3%), while total motile organisms dominated the diseased sites (43.7% vs. 4.8%). In the diseased sites between appointments No. 1 and No. 4 there was a reduction in the number of motile organisms, 43.7% to 14.0%, and an increase in coccoid cells from 18.3% to 41.5%. Counts of colonies grown on medium largely selective for Bacteroides species dropped markedly in both the healthy and diseased sites, especially at the end of initial therapy. High proportions of coccoid cells correlated with health and motile forms with disease. Discriminant analysis using coccoid cells and total motile organisms suggested that these bacterial categories were reliable for classifying healthy and diseased sites, respectively. Microscopic evaluation of subgingival flora was found to be an accurate and convenient means to evaluate the presumptive activity of periodontal lesions and to monitor progress of therapy.