1. Department of Prosthodontics and Materials Science, School of Dentistry, University of Leipzig, Nürnberger Str. 57, 04103 Leipzig, Germany;
2. Department of Dental Public Health Sciences, School of Dentistry, University of Washington, Seattle, WA 98195-7475, USA;
3. Center for Health Studies, Group Health Cooperative, 1730 Minor Avenue, Suite 1600, Seattle, WA 98101-1448, USA, and Department of Biostatistics, University of Washington, Seattle, WA 98195-7232, USA;
4. Department of Oral Medicine, School of Dentistry, University of Washington, Seattle, WA 98195-6370, USA;
5. Department of Epidemiology and Department of Health Services, School of Public Health and Community Medicine, University of Washington, Seattle, WA 98195-7236, USA; and