1. Department of Histology, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271–8587, Japan
2. Department of Liberal Arts(Biology), Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271–8587, Japan
3. Research Institute of Oral Science, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271–8587, Japan