1. Department of Restorative Sciences, Faculty of Dentistry, Kuwait University, P.O. Box 24923, Safat 13110, Kuwait
2. Department of Clinical Dentistry-Prosthodontics, Faculty of Medicine and Dentistry, University of Bergen, Arstadveien 17, 5009 Bergen, Norway
3. Department of Clinical Dentistry-Cariology, Faculty of Medicine and Dentistry, University of Bergen, Arstadveien 17, 5009 Bergen, Norway
4. Department of Prosthetic Dentistry/Dental Materials Science, Institute of Odontology, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, P.O. Box 450, SE 405 30, Sweden