1. Department of Preventive and Community Dentistry, School of Dentistry, Pusan National University, Yangsan, Korea.
2. BK21 PLUS Project, School of Dentistry, Pusan National University, Yangsan, Korea.
3. Department of Dental Hygiene, College of Health and Medical Sciences, Cheongju University, Cheongju, Korea.
4. Department of Periodontology, School of Dentistry, Pusan National University, Yangsan, Korea.