1. Department of Preventive Dentistry, School of Dentistry, Ohu University, 31-1 Misumido, Tomitamachi, Koriyama, Fukushima 963-8611, Japan
2. Department of Oral Function and Molecular Biology, School of Dentistry, Ohu University, Koriyama, Japan
3. Department of Oral Medical Sciences, School of Dentistry, Ohu University, Koriyama, Japan
4. Department of Virology, Toyama Institute of Health, Imizu, Japan