1. Department of Biomaterials, Institute of Clinical Dentistry, University of Oslo, 0317 Oslo, Norway
2. Department of Prosthetics and Oral Function, Institute of Clinical Dentistry, University of Oslo, 0317 Oslo, Norway
3. Section of the Postgraduate Program in Periodontology, Faculty of Dentistry, Complutense University of Madrid (UCM), 28040 Madrid, Spain