1. Department of Plastic, Reconstructive, Hand and Burn Surgery; Bogenhausen Academic Hospital, Technische Universität München; Munich 81925 Germany
2. Department of Oral and Maxillofacial Surgery; Technische Universität München, Klinikum rechts der Isar; Munich 81675 Germany
3. Institute of Medical Statistics and Epidemiology, Technische Universität München; Munich 81675 Germany