1. Unit of Periodontology; Department of Oral Health Sciences; University of Leuven; Kapucijnenvoer Belgium
2. Scientific Institute of Public Health; Brussels Belgium
3. Department of Oral and Maxillofacial Surgery; Sahlgrenska Academy; University of Gothenburg; Göteborg Sweden
4. Department of Oral and Maxillofacial Plastic Surgery; University of Würzburg; Würzburg Germany
5. Department of Oral and Maxillofacial Surgery; Institute of Surgical Sciences; Uppsala University; Uppsala Sweden