1. Finnish Institute of Occupational Health, Department of Epidemiology and Biostatistics, Topeliuksenkatu 41a A, 00250 Helsinki, Finland;
2. Finnish Institute of Occupational Health, Department of Occupational Medicine, Helsinki, Finland;
3. Finnish Institute of Occupational Health, Department of Physiology, Helsinki, Finland;
4. Institute of Dentistry, University of Helsinki, Helsinki, Finland; and
5. Department of Radiology, Peijas Hospital, Helsinki University Central Hospital, Vantaa, Finland