1. Department of Anatomy and Histology, School of Dental Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104
2. Department of Anatomy, Okayama University Dental School, Okayama City 700, Japan
3. Department of Oral Pathology, Tokushima University Dental School, Tokushima City 770, Japan
4. Department of Biological Science and Technology, Faculty of Engineering, University of Tokushima, Tokushima City 770, Japan
5. Department of Pharmacology, Kawasaki Medical School, Kawasaki City 701‐01, Japan