1. Department of Oral Biology & Oral Science Research Center, BK21 Project for Medical Sciences, Yonsei University College of Dentistry, Shinchon-dong 134, Seodaemoon-gu, Seoul 120-752, Korea; and
2. Department of Physiology and Research Institute of Oral Science,
Nihon University School of Dentistry at Matsudo, Matsudo, Chiba, Japan;