1Department of Periodontology, College of Dentistry and Dental Research Institute, Seoul National University, Korea.
2Department of Preventive & Public Health Dentistry, College of Dentistry, Seoul National University, Korea.
Corresponding author: Soo-Boo Han, Department of Periodontology, College of Dentistry, Seoul National University, 28 Yongun-Dong, Chongno-Ku, Seoul, 110-749, Korea. perioh@snu.ac.kr