1. Department of Anesthesia, Harvard Medical School/Children's Hospital, Boston Massachusetts, 02115
2. Department of Clinical Oral Physiology, Dental School, Århus University, DK-8000 Århus C, Denmark
3. Laboratory for Experimental Pain Research, Center for Sensory-Motor Interaction, Aalborg University, DK-9220, Denmark
4. Department of Anesthesia, Aalborg Hospital, DK-9000 Aalborg, Denmark
5. Faculty of Dentistry, University of Toronto, Toronto, Ontario, M5G 1G6 Canada