1. Hamamatsu-city Oral Health and Care Center, 2-11-2 Kamoe, Naka-ku, Hamamatsu 432-8550, Japan;
2. Department of Advanced Prosthodontics, Hiroshima University Graduate School of Biomedical Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan;
3. Department of Microbiology, Institute of Health Biosciences, Tokushima University Graduate School, 3-18-15 Kuramoto-cho, Tokushima 770-8504, Japan; and
4. School of Nursing and Rehabilitation Sciences, Showa University, Tokaichiba-cho, Midori-ku, Yokohama 226-8555, Japan