1Department of Periodontology, School of Dentistry, Seoul National University, Korea.
2Department of Periodontics, Samsung Medical Center, School of Medicine, Sungkyunkwan University, Korea.
Corresponding author: In-Chul Rhyu, Department of Periodontology, College of Dentistry, Seoul National University, 28 Yongon-Dong, Chongno-Ku, Seoul, 110-744, South Korea. icrhyu@snu.ac.kr