1. Department of Community Oral Health, School of Dentistry, Asahi University, 1851 Hozumi, Mizuho, Gifu 501-0296, Japan
2. Department of Microbiology and Immunology, Columbia University Medical Center, 701 West 168th Street, New York 10032, NY, USA
3. Department o f Oral Health and Preventive Dentistry, Meikai University School of Dentistry, Sakado, Saitama 350-0283, Japan
4. Asahi University Hospital, 3- 23 Hashimoto-cho, Mizuho, Gifu 500-8523, Japan