G Guzzi1, F Spadari2, G P Bombeccari2, P D Pigatto3. 1. Italian Association for Metals and Biocompatibility Research - A.I.R.M.E.B., Milan, Italy. Electronic address: gianpaolo_guzzi@fastwebnet.it. 2. Department of Biomedical, Surgical and Dental Sciences, Unit of Oral Pathology and Medicine, Ospedale Maggiore Policlinico Fondazione Ca' Granda IRCCS, University of Milan, Milan, Italy. 3. Department of Biomedical, Surgical and Dental Sciences, Unit of Oral Pathology and Medicine, IRCCS Galeazzi Hospital, University of Milan, Milan, Italy.