1. Department of Ultrastructural Science; Tokyo Dental College; Masago 1-2-2; Mihamaku; Chiba-City; Chiba; 261-8502; Japan
2. Department of Morphological Biology (Cell Biology and Oral Histology); Ohu University School of Dentistry; 31-1 Misumido; Tomitamachi; Koriyama; 963-8611; Japan
3. Department of Anatomy; Tokyo Dental College; Masago 1-2-2; Mihamaku; Chiba-city; Chiba; 261-8502; Japan
4. Department of Cytology and Histology; Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences; 2-5-1 Shikatacho; Okayama; 700-8558; Japan