1. Departments of Materials Science and Metallurgy and 3Statistics and Operations Research, ETSEIB, Universitat Politecnica de Catalunya, Av. Diagonal 647, 08028 Barcelona, Spain
2. Department of Dental Materials Science, University Hospital, University Ghent, De Pintelaan 185, B-9000 Ghent, Belgium, Senior Research Assistant of the N.F.S.R. (Belgium)
3. Department of Dental Materials Science, University Hospital, University Ghent, De Pintelaan 185, B-9000 Ghent, Belgium