1Department of Periodontology, College of Dentistry, Yonsei University, Seoul, Korea.
2Research Institute for Periodontal Regeneration, College of Dentistry, Yonsei University, Seoul, Korea.
3Brain Korea 21 project for medical science, Yonsei University, Seoul, Korea.
Corresponding author: Chong-Kwan Kim, Department of Periodontology, College of Dentistry, Yonsei University 134 Shinchon-Dong, Seodaemun-Gu, Seoul, Korea. Tel: +82-2-361-8830, Fax: +82-2-392-0398, ckkim@yumc.yonsei.ac.kr