Background: Porphyromonas gingivalis is a major periopathogen that involved in the pathogenesis of chronic periodontitis. Cigarette smoking is a major risk factor in the development and further progression of periodontal diseases. Methods: 163newly diagnosed chronic periodontitis patients were recruited randomly from patients attending Khartoum Teaching Dental Hospital according to criteria (pocket depth ≥ 5 & bleeding on probing). 89 were non-smokers while 74 were smokers. The two groups were examined clinically for indicators of periodontal health status. Plaque Index, Gingival Index [Probable Pocket Depth, Gingival Recession, Clinical Attachment Loss, Furcation Involvement and Tooth Mobility scores. The subgingival plaque samples were obtained from each subject, DNA extraction of P.gingivalis and quantification with SYBR Green I assay real-time PCR technology was done. Results: Different means of periodontal health indicators showed highly significant differences between smokers and non-smokers using t-test (P < 0.001). In contrast to non-smokers, smokers tend to have more plaque accumulation, less gingival bleeding, deep probable pockets, severe gingival recession, advanced clinical attachment loss, worst furcation involvement and more tooth mobility. The mean log-transformed of absolute counts of P. gingivalis in subgingival plaque samples from the smokers was 212.93 44.95CN/1000 copies while the figure for non-smokers was 37.30 5.24CN/1000 copies using Independent t-test (P = 0.001). Conclusion: Smokers showed more plaque accumulation, gingival recession, pocket depth, clinical attachment loss, furcation involvement tooth mobility but less gingival bleeding than non-smokers. Tobacco smoking modifies subgingival microbiota particularly P.gingivalis in chronic periodontitis patients.
