Department of Preventive Dentistry, Faculty of Dental Science, Kyushu University, Fukuoka-shi, Japan. yosh@dent.kyushu-u.ac.jp|Department of Preventive Dentistry, Faculty of Dental Science, Kyushu University, Fukuoka-shi, Japan. yosh@dent.kyushu-u.ac.jp|Department of Preventive Dentistry, Faculty of Dental Science, Kyushu University, Fukuoka-shi, Japan. yosh@dent.kyushu-u.ac.jp