1Department of Periodontology, College of Dentistry, Seoul National University, Korea.
2Department of Oromaxillofacial Infection and Immunity, Seoul National University, Korea.
3Division of Periodontology, Department of Oral Biological Science, Niigata University, Japan.
Corresponding author: Chong-Pyoung Chung. Department of periodontology, College of Dentistry, Seoul National University, 28, Yongon-Dong, Chongno-Gu, 110-749, Seoul.