1. Department of Periodontology, School of Dentistry, Kyung Hee University, Private Practice in Periodontics and Implant Dentistry, Seoul 02771, Korea
2. Division of Periodontics, Section of Oral, Diagnostic and Rehabilitation Sciences, Columbia University College of Dental Medicine, New York, NY 10032, USA
3. Department of Periodontology, Division of Dentistry, College of Medicine, Hanyang University, Seoul 04763, Korea