1. From the Division of Epidemiology and Health Services Research, Institute of Biostatistics, Epidemiology, and Informatics, University Medical Centre, Mainz, Germany; Department of Radiation Oncology, University Medical Centre Groningen, University of Groningen, The Netherlands; Department of Oral & Maxillofacial Surgery, Sheba Medical Centre, Tel-Hashomer, and Department of Oral Pathology and Oral Medicine, School of Dental Medicine, Tel-Aviv University, Tel-Aviv, Israel.