1. Department of Conservative Dentistry, Dental Research Institute and School of Dentistry, Seoul National University, Jongno-gu, Yeongun-dong 275-1, Seoul 110-749, Republic of Korea
2. Department of Family Medicine, Eulji University School of Medicine, Joong-gu, Yongdu-dong 143-5, Daejeon, Republic of Korea
3. School of Dentistry, David Geffen School of Medicine, Jonsson Comprehensive Cancer Center, UCLA, Los Angeles, CA 90095, USA