Department of Internal Medicine and Institute of Gastroenterology;
Yonsei University College of Medicine;
Seoul 03722;
South Korea;
Department of Internal Medicine;
Gangnam Severance Hospital;
Yonsei University College of Medicine;
Seoul 06229;
South Korea;
Department of Internal Medicine;
Bundang CHA Medical Center;
CHA University School of Medicine;
Seoul 13496;
South Korea;
Department of Statistics and Actuarial Science;
Soongsil University;
Seoul 06978;
South Korea;
Department of Internal Medicine and Liver Research Institute;
Seoul National University College of Medicine;
Seoul 03080;
South Korea;
Department of Periodontics;
the Catholic University of Korea College of Medicine;
Seoul 06591;
South Korea;
Inflammatory bowel disease; Periodontitis; Smoking; Ulcerative colitis; Crohn’s disease;