1. Faculty of DentistryDepartment of Oral Biology, University of Oslo, Oslo, Norway
2. Department of PeriodontologyThe Forsyth Institute, Cambridge, MA, USA
3. Department of BiostatisticsInstitute of Basic Medical Sciences, University of Oslo, Oslo, Norway
4. Department of Infectious Disease EpidemiologyDivison of Infectious Disease Surveillance, Norwegian Institute of Public Health, Oslo, Norway