1. Department of Preventive Dentistry, Kyushu University Faculty of Dental Science, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
2. Department of Preventive Dentistry, Kyushu Dental College, 2-6-1 Manazuru, Kokurakita-ku, Kitakyushu 803-8580, Japan
3. Department of Preventive Dentistry, Niigata University School of Dentistry, 2-5274 Gakkocho-dori, Niigata 951-8514, Japan