1. Department of Cranio-Maxillo-Facial-Surgery, University Hospital Ulm, 89081 Ulm, Germany
2. Department of Cranio-Maxillo-Facial-Surgery, German Armed Forces Hospital Ulm, 89081 Ulm, Germany
3. Medical Statistics and Biomathematics, University Medical Centre Mannheim, Heidelberg University, 68167 Mannheim, Germany
4. Department of Otolaryngology, Head and Neck Surgery, German Armed Forces Hospital Ulm, 89081 Ulm, Germany
5. Department of Cranio-Maxillo-Facial-Surgery, Ludwigshafen Hospital, 67063 Ludwigshafen, Germany