1. Department of Oral Health, Yecheon Public Health Center, Yecheon, Korea.
2. Department of Preventive Medicine, College of Medicine, The Catholic University of Korea, Seoul, Korea.
3. Department of Periodontology, College of Dentistry, Kyung Hee University, Seoul, Korea.
4. Department of Oral Biochemistry and Molecular Biology, College of Dentistry, Kyung Hee University, Seoul, Korea.