1 Department of Health Policy Science, Graduate School of Medical Science, Yamagata University, Yamagata, Japan.
2 Department of International and Community Oral Health, Tohoku University Graduate School of Dentistry, 4-1, Seiryo-machi, Aoba-ku, Sendai, Miyagi, 980-8575, Japan.
3 Department of International and Community Oral Health, Tohoku University Graduate School of Dentistry, 4-1, Seiryo-machi, Aoba-ku, Sendai, Miyagi, 980-8575, Japan. tsubo828@gmail.com.