1. Section of Experimental Dento-Maxillo-Facial Medicine, Center of Dento-Maxillo-Facial Medicine, University of Bonn, Bonn, Germany
2. Department of Periodontology and Operative Dentistry, University Medical Center of the Johannes Gutenberg University, Mainz, Germany
3. Center of Electron Microscopy, University Hospital Jena, Jena, Germany
4. Department of Periodontology, Laboratory of Oral Microbiology, University of Bern, Bern, Switzerland