The occurrence of Actinobacillus actinomycetemcomitans, Bacteroides gingivalis, Bacteroides intermedius and spirochaetes in the subgingival microflora of adolescents and their relationship with the amount of supragingival plaque and gingivitis

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The subgingival microflora of 89 children aged 14–15 years was investigated by anaerobic culture and dark‐field microscopy. Actinobacillus actinomycetemcomitans was isolated from 13 subjects and black‐pigmented Bacteroides from 83 subjects. B. intermedius was the most commonly isolated Bacteroides species and was identified in 76 subjects, whereas B. gingivalis was observed in only two subjects. Spirochaetes were found in 79 of the subjects. No statistically significant differences in the clinical condition of the subjects were noted in relation to the presence or absence of A. actinomycetemcomitans. Statistically significant direct relationships were observed between the number of sites with clinical signs of gingivitis and the proportion of spirochaetes and the number and proportion of black‐pigmented Bacteroides in the subgingival sample. These relationships were independent of the effect of the amount of supragingival plaque on either gingivitis or the composition of the subgingival flora.