1. Research Team for Promoting Independence and Mental Health, Tokyo Metropolitan Institute for Geriatrics and Gerontology, 35-2 Sakae-cho, Itabashi-ku, Tokyo 173-0015, Japan
2. School of Health Sciences, Meikai University, 1 Meikai, Urayasu-shi, Chiba 279-8550, Japan
3. Gerodontology, Department of Oral Health Science, Hokkaido University, Kita 13-jo Nishi 7-chome, Kita-ku, Sapporo-shi, Hokkaido 060-8586, Japan
4. Dentistry and Oral Surgery, Tokyo Metropolitan Geriatric Hospital, 35-2 Sakae-cho, Itabashi-ku, Tokyo 173-0015, Japan