1. Department of Oral Biomaterials and Technology, School of Dentistry, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan; and
2. Division of Aesthetic Dentistry, Showa University School of Dentistry, 2-1-2, Kitasenzoku, Ohta-ku, Tokyo 145-8515, Japan