BACKGROUNDThe association between the infection of Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans and Treponema denticola in chronic periodontitis (CP) and the severity of periodontal disease remains to be elucidated. The aim of this study was to investigate the subgingival infection frequencies of three periodontopathic bacteria in Chinese CP patients and to evaluate the correlations between infection by these bacteria and periodontal destruction.

METHODSA multiple PCR assay using primers derived from 16SrDNA genes of P. gingivalis, A. actinomycetemcomitans and T. denticola was established to measure simultaneously the presence of the three microbes in 162 subgingival samples from 81 Chinese CP patients.

RESULTSThe positive rates of P. gingivalis, A. actinomycetemcomitans and T. denticola in the subgingival samples were 84.6%, 83.3% and 88.3%, respectively. Of the subgingival samples, 68% revealed the coinfection of all the three microbes. The infection rates with P. gingivalis, A. actinomycetemcomitans or T. denticola alone was 5.9% (1/17), 17.6% (3/17) and 76.5% (13/17), respectively. A close association was present between the A. actinomycetemcomitans infection and gingival index (GI) (P < 0.01), but not between P. gingivalis or T. denticola infection and GI (P > 0.05). P. gingivalis and A. actinomycetemcomitans were more frequently detectable in middle and deep pockets than in shallow ones (P < 0.01), while T. denticola was found remarkably often in deep pockets (P < 0.05). The coinfection rate of the three microbes was significantly higher in sites with severe periodontitis than in those with mild periodontitis (P < 0.01).

CONCLUSIONSThe multiple PCR established in this study can be used as a sensitive and specific method to simultaneously detect all three microbes in subgingival samples. A. actinomycetemcomitans infection may be associated with CP and play an important role in the periodontal tissue destruction. The coinfection of P. gingivalis, A. actinomycetemcomitans and T. denticola can cause more serious periodontal destruction than infection of any one or two of the three microbes.