1. Department of Dental Materials, Nihon University, School of Dentistry
at Matsudo, 870-1 Sakaecho, Nishi 2, Matsudo, Chiba 271-8587, Japan; and
2. Department of Biomaterials, Okayama University, Graduate School of
Medicine and Dentistry, 2-5-1 Shikadacho, Okayama, Okayama 700-8525, Japan;