1. Department of Pediatric Dentistry, School of Dentistry, Showa University, Shinagawa-ku 142-8555, Japan
2. Department of Pharmacology, School of Dentistry, Showa University, Shinagawa-ku 142-8555, Japan
3. Department of Oral Anatomy, School of Dentistry, Showa University, Shinagawa-ku 142-8555, Japan
4. Bioscience Laboratories, Meiji Seika Kaisha, Ltd., Sakado 350-0289, Japan