1. Department of Medical Biochemistry, Oslo University Hospital, Kirkeveien 166, P.O. Box 4956, Nydalen, 0424 Oslo, Norway
2. Faculty of Medicine, University of Oslo, Sognsvannsveien 9, 0372 Oslo, Norway
3. Department of Oral Biology, Faculty of Dentistry, University of Oslo, Sognsvannsveien 10, P.O. Box 1052, Blindern, 0316 Oslo, Norway