1. Department of Substitutive Dental Sciences, College of Dentistry, Dammam University, P.O. Box 1982, Dammam 31411, Saudi Arabia
2. Department of Prosthodontics, Faculty of Dentistry, Alexandria University, P.O. Box 21500, Alexandria, Egypt
3. Department of Community Dentistry, Institute of Dentistry, University of Oulu, P.O. Box 5281, 90014 Oulu, Finland
4. Oral and Maxillofacial Department, Oulu University Hospital, Finland
5. Department of Prosthetic Dentistry and Stomatognathic Physiology, Institute of Dentistry, University of Oulu, P.O. Box 5281, 90014 Oulu, Finland