1. Department of Oral Health Science, Graduate School of Dental Medicine, Hokkaido University Graduate School of Dental Medicine, Kita 13, Nishi 7, Kita-ku, Sapporo 060-8586, Japan;
2. Department of Oral Rehabilitation, Medical College of Georgia, Augusta, GA 30912-1260; and
3. Department of Oral Functional Science, Hokkaido University Graduate School of Dental Medicine, Sapporo, Japan;