Relationship between the percentage of subgingival spirochetes and the severity of periodontal disease.

The purpose of this study was to determine the correlations between various clinical assessments of inflammatory periodontal disease and the percentage of motile bacteria in the subgingival flora of sites representing widely varying states of periodontal disease. Darkfield microscopy was used to determine the percentage of spirochetes and other motile bacteria at two sites from each of 60 volunteers. For each site the following clinical assessments were recorded: Plaque Index (PII), gingival exudate (GE), Gingival Index (GI), bleeding tendency (BT), pocket depth (PD), connective tissue attachment loss (AL) and Periodontal Disease Index (PDI). Statistically significant (P less than 0.001) positive correlations (r) were found between the percentage of subgingival spirochetes and PII (r=0.54), GE (r=0.61), GI (r=0.57), BT (r=0.59), PD (r=0.56), AL (r=0.56) and PDI (r=0.61). Clinically healthy sites harbored much lower percentages of motile bacteria than did clinically disease sites. Most of the observed variation in the percentage of motile bacteria could be accounted for by variations in the percentage of spirochetes. The most significant increases in the relative percentages of subgingival spirochetes occurred when bleeding upon probing was observed as a sign of inflammation and/or when pocket depth and attachment loss exceeded 3 mm.