1. Department of Periodontics and Oral Medicine; University of Michigan School of Dentistry; Ann Arbor MI USA
2. Clinic of Fixed and Removable Prosthodontics and Dental Material Science; University of Zurich; Zurich Switzerland
3. Department of Oral Surgery; Universitätsklinikum Düsseldorf; Düsseldorf Germany
4. Department of Oral Surgery and Implantology; Carolinum; Johann Wolfgang Goethe-University Frankfurt; Frankfurt Germany