[1] UCL, Eastman Dent Inst Oral Hlth Care Sci, Dept Oral Med, London WC1X 8LD, England
[2] Univ Turin, Dept Oral Med & Periodontol, Sch Med & Dent, Turin, Italy
[3] Cent Publ Hlth Lab, Div Virus Reference, London, England
[4] Univ G dAnnunzio, Dept Oral Med, Chieti, Italy