1. Department of Operative Dentistry and Periodontology, University of Freiburg, Hugstetter Str. 55, D‐79102 Freiburg, Germany
2. Department of Operative Dentistry, Preventive Dentistry and Periodontology, University of, Göttingen, Robert‐Koch‐Str. 40, D‐37075 Göttingen, Germany
3. Clinic of Preventive Dentistry, Periodontology and Cariology, University of Zurich, Platterstr. 11, CH 8032 Zurich, Switzerland
4. Clinic of Operative Dentistry, Periodontology and Preventive Dentistry, University Hospital, Saarland University, Building 73, D‐66421 Homburg/Saar, Germany