1. Removable Partial Prosthodontics, Graduate School of Medical and Dental Sciences; Tokyo Medical and Dental University, 1-5-45 Yushima; Bunkyo-ku Tokyo 113-8549 Japan
2. Institute of Biomaterials and Bioengineering; Tokyo Medical and Dental University, 2-3-10 Kanda-Surugadai; Chiyoda-ku Tokyo 101-0062 Japan
3. Graduate School of Engineering; The University of Tokyo, Bunyko; Tokyo 113-8656 Japan