1. Department of Periodontology; Faculty of Dentistry; University of Münster; Münster Germany
2. Department of Conservative Dentistry; Dental School Ruprecht-Karls-University of Heidelberg; Heidelberg Germany
3. Max Planck Institute for Social Law and Social Policy; Munich Center for the Economics of Aging; Munich Germany
4. Institute of Epidemiology and Preventive Medicine; College of Public Health; National Taiwan University; Taipei Taiwan