1. Division of Fixed Prosthodontics, Department of Restorative & Biomaterials Sciences Meikai University School of Dentistry Sakado Saitama Japan
2. Department of Dental Materials Sciences, School of Life Dentistry at Tokyo The Nippon Dental University Tokyo Japan
3. Department of Prosthetic Dentistry and Biomaterials Science, Institute of Dentistry University of Turku Turku Finland
4. Department of Dental Materials Nihon University School of Dentistry Tokyo Japan