Objective This study aimed to assess the relationship between the distributions of Haemophilus aggregati-bacter (H. aggregatibacter ), Porphyromonas gingivalis (P. gingivalis ), Prevotella intermedia (P. intermedia), Tannerella forsythensis (T. forsythensis ), and Treponema denticola (T. denticola) in subgingival plaque and different periodontal con-ditions of chronic periodontitis.Methods Twenty patients (80 sites) with chronic periodontitis and ten healthy subjects (20 sites) were included. The study sites were distributed into different groups according to the differences in their pocket probing depths (PD). The groups were described as follows: group A, PD≤4 mm; group B, 4 mm＜PD≤6 mm; group C, PD＞6 mm. Semi-quantification of the subgingival microorganism samples was analyzed by polymerase chain reaction (PCR) and reverse hybridization assay.Results The prevalence rates and quantities of P. gingivalis, P. intermedia, T. forsythensis, and T. den-ticola were significantly higher in groups B and C than in the healthy group. Higher prevalence rates and quantities of P. gingivalis were detected in group A than in the healthy group. The quantities of T. forsythensis and T. denticola were also significantly higher in group C than in group B. However, the prevalence rates and quantities of H. aggregatibacter showed no significant difference among the groups.Conclusion The prevalence rates and levels of P. gingivalis, P. intermedia, T. forsythensis, and T. denticola possibly increased as the depths of the periodontal pockets increased. The quantity of P. gingi-valis was correlated with the early stage of chronic periodontitis. The quantities of T. forsythensis and T. denticola were asso-ciated with local development of moderate or severe chro-nic periodontitis.
