1Department of periodontology, College of Dentistry, Seoul National University, Korea.
2Intellectual Biointerface Engineering Center, Seoul National University, Korea.
Corresponding author: Young Ku, Depantment of periodonology, College of Dentistry, Seoul National University, 28 Yongon-Dong, Chongno-Ku, Seoul, 110-749, Korea. guy@snu.ac.kr