1. 'Dept. of Preventive Dentistry, Kyushu University Faculty of Dental Science, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan, -u.ac.jp
2. 'Dept. of Preventive Dentistry, Kyushu University Faculty of Dental Science, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
3. Fukuoka Health Promotion Foundation, 2-5-1 Maizuru, Chuo-ku, Fukuoka 810-0073, Japan; corresponding author