1Department of Periodontology, College of Dentistry, Seoul National University, Korea.
2Dental Resarch Institute, College of Dentistry, Seoul National University, Korea.
Corresponding author: Yong-Moo Lee, Department of Periodontology, College of Dentistry, Seoul National University, 28, Yongon-Dong, Chongno-Gu, 110-749, Seoul, Korea.