1. Department of Histology, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271–8587, Japan
2. Nihon University Graduate School of Dentistry at Matsudo, Histology, Cytology and Developmental Anatomy, Matsudo, Chiba 271–8587, Japan
3. Department of Removable Prosthodontics and Geriatric Oral Health, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271–8587, Japan
4. Department of Oral Surgery, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271–8587, Japan