1. Department of Histology, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271 - 8587, Japan
2. Laboratory for Electron Beam Research and Application(LEBRA), Institute of Quantum Science, Nihon University, Funabashi, Chiba 274 - 8501, Japan
3. Department of Operative Dentistry, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271 - 8587, Japan
4. Nihon University Graduate School of Dentistry at Matsudo, Histology and Embryology, Matsudo, Chiba 271 - 8587, Japan