1Department of Periodontology, College of Dentistry, Seoul National University, Korea.
2Department of Prosthodontics, Yong Dong Sevrance Hospital, Yonsei University, Korea.
3Department of Prosthodontics, College of Dentistry, Seoul National University, Korea.
Corresponding author: In-Chul Rhyu, Department of Periodontology, College of Dentistry, Seoul National University, 28 Yongon-Dong, Chongno-Ku, Seoul, 110-744, South Korea. Fax:82-2-744-0051, icrhyu@snu.ac.kr