Won-Bae Park1,2, Kyung Lhi Kang1, Ji-Young Han3. 1. Department of Periodontology, School of Dentistry, Kyung Hee University, Seoul, Korea. 2. Private practice in periodontics and implant dentistry, Seoul, Korea. 3. Department of Dentistry and Periodontology, Hanyang University College of Medicine, Seoul, Korea.