1. Department of Periodontology, Seoul National University School of Dentistry, Seoul 03080, Korea
2. Department of Bioengineering, University of California, Los Angeles, CA 90095, USA
3. Department of Prosthodontics, School of Dentistry and Dental Research Institute, Seoul National University, 101 Daehak-Ro, Jongro-Gu, Seoul 03080, Korea