1. Nanomaterials Research
Institute, National Institute of Advanced Industrial Science and Technology (AIST), Central 5-41, 1-1-1 Higashi, Tsukuba 305-8565, Japan
2. Department of Periodontology and Endodontology, Faculty of Dental
Medicine, Hokkaido University, N13W7, Kita-ku,
Sapporo 060-8586, Japan