1 Professor, Department of Preventive and Public Health Dentistry, Fukuoka Dental College, Fukuoka 814-0193, Japan. Electronic address: haniokat@college.fdcnet.ac.jp.
2 Assistant Professor, Department of Preventive Dentistry, Graduate School of Dentistry Osaka University, Osaka 565-0871, Japan. Electronic address: ojima@dent.osaka-u.ac.jp.
3 Associate Professor, Department of Preventive Medicine and Public Health, Faculty of Medicine, Fukuoka University, Fukuoka 814-0180, Japan. Electronic address: k-tanaka@fukuoka-u.ac.jp.