1. Department of Prosthetic Dentistry/Dental Materials Science, Institute of Odontology, Sahlgrenska Academy, University of Gothenburg, Medicinaregatan 12 F, P.O. Box 450, 40530 Gothenburg, Sweden
2. Department of Prosthetic Dentistry, University of Oslo, 0161 Oslo, Norway
3. Department of Prosthetic Dentistry, Postgraduate Dental Education Center, P.O. Box 1126, 70111 Örebro, Sweden
4. School of Health and Medical Sciences, Örebro University, 70281 Örebro, Sweden