1. Department of Dental Hygiene, College at Niigata, The Nippon Dental University, 1-8 Hamaura cho, Chuo-ku, Niigata 951-8580, Japan
2. Department of Preventive and Community Dentistry, School of Life Dentistry at Niigata, The Nippon Dental University, 1-8 Hamaura cho, Chuo-ku, Niigata 951-8580, Japan
3. Department of Dental Anesthesiology, School of Life Dentistry at Niigata, The Nippon Dental University, 1-8 Hamaura cho, Chuo-ku, Niigata 951-8580, Japan