1. Department of Endodontics, School of Dentistry, University of North Carolina, Chapel Hill, North Carolina 27514, USA;
2. NIOM, Forskningsveien 1, 0371 Oslo 3, Norway;
3. Georgetown University, School of Dentistry, 3900 Reservoir Road NW Washington DC 20007, USA;
4. University of Michigan, School of Dentistry. Ann Arbor, Michigan 48109, USA;
5. Columbia University. School of Dentistry, Department of Endodontics, 630 West 168th Street, New York New York 10032, USA;
6. University of Toronto, Faculty of Dentistry, 124 Edward Street, Toronto, Ontario, Canada M5G 1G6;
7. University of Pennsylvania, School of Dental Medicine, 4001 Spruce Street. Philadelphia, Pennsylvania 19104, USA