1. Department of Prosthodontics, University Medical Center Goettingen, Goettingen, Germany.
2. Private Practice, Weilburg, Germany.
3. Department of Cariology, Endodontology and Periodontology, University Leipzig, Leipzig, Germany.
4. Department of Medical Statistics, Georg-August-University, Goettingen, Germany.
5. School of Health and Society, Kristianstad University, Kristianstad, Sweden.