1. Department of Oral Biology, Yonsei University, Seoul 120-752, Korea.
2. Oral Science Research Center, Yonsei University, Seoul 120-752, Korea.
3. College of Dentistry, Yonsei University, Seoul 120-752, Korea.
4. Department of Physiology, College of Medicine, Chungnam National University, Daejeon 305-764, Korea.
5. Department of Orthodontics, Yonsei University, Seoul 120-752, Korea.
6. Department of Oral Microbiology, College of Dentistry, Chonnam National University, Gwangju 500-757, Korea.
7. Brain Korea 21 Project of Dental Science, Yonsei University, Seoul 120-752, Korea.