1. Nihon University Graduate School of Dentistry at Matsudo, Histology, Cytology and Developmental Anatomy, Matsudo, Chiba 271-8587, Japan
2. Departments 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
4. Division of Companion Diagnostics, Department of Pathology of Microbiology, Nihon University School of Medicine, Itabashi, Tokyo 173-8610, Japan
5. Departments of Histology, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271-8587, Japan