It has shown that compared to Porphyromonas gingivalis negative subjects, positive subjects exhibited a significant increase in the number of aneurysms, and a notable overexpression of S100A9 was detected on the smooth muscle cells surface of damaged vessels, indicating that P. gingivalis might promote the occurrence and development of aortic aneurysms through upregulating S100A9.115. The gene discussed is S100A9; the disease is aortic aneurysm.