Objective To analyze the periodontal status and serum interleukin 6 (IL-6), matrix metalloproteinase 8 (MMP-8) and MMP-9 levels in patients with combined periodontic-endodontic lesions. 〖WTHZ〗Methods A total of 108 patients with combined periodontic-endodontic lesions were selected as the experimental group, including 50 patients receiving dental pulp and periodontal treatment (experimental group 1) and 58 patients without treatment (experimental group 2). Meanwhile, 50 healthy individuals who underwent orthodontic tooth extraction were selected as the control group. The detection rate of pathogenic bacteria in periodontal pocket, distribution of pathogenic bacteria, serum IL-6, MMP-8 and MMP-9 levels were compared among the 3 groups. Logistic regression model was used to analyze the relationship between serum IL-6, MMP-8 and MMP-9 and combined periodontic-endodontic lesions. Results The detection rate of pathogenic bacteria in periodontal pocket of the experimental group 2 was significantly higher than that in the experimental group 1 and that in the control group (P＜0.05). However, there was no significant difference between the experimental group 1 and the control group (P＞0.05). The main pathogenic bacteria in periodontal pocket of the experimental group 2 included Bacteroides forsythus (27.59%), Prevotella intermedia (18.97%) and Porphyromonas gingivalis (15.52%). The detection rates of Bacteroides forsythus, Prevotella intermedia and Porphyromonas gingivalis in the experimental group 2 were significantly higher than those in the experimental group 1 and the control group (P＜0.05). Serum IL-6, MMP-8 and MMP-9 levels in the experimental group 2 were significantly higher than those in the experimental group 1 and the control group (P＜0.05). Logistic regression analysis found that elevated serum IL-6, MMP-8 and MMP-9 levels were risk factors for combined periodontic-endodontic lesions (P＜0.05). Conclusion Patients with combined periodontic-endodontic lesions have a higher incidence of infection. Bacteroides forsythus, Prevotella intermedia and Porphyromonas gingivalis are main pathogenic bacteria. Abnormally elevated serum IL-6, MMP-8 and MMP-9 levels are risk factors for combined periodontic-endodontic lesions