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.