1. Department of Periodontology, Institute of Odontology, Sahlgrenska Academy; University of Gothenburg; Gothenburg Sweden
2. Department of Periodontology, Operative and Preventive Dentistry; University of Bonn; Bonn Germany
3. Clinic of Cranio-Maxillofacial and Oral Surgery; University of Zurich; Zurich Switzerland
4. Department of Oral & Maxillofacial Surgery; Red Cross Hospital; Kassel Germany