1. Department of Preventive Dentistry, Periodontology and Implant Biology, Dental School, Aristotle University of Thessaloniki, Thessaloniki, Greece
2. Department of Periodontology, 424 General Military Training Hospital, Thessaloniki, Greece
3. Department of Oral and Maxillofacial Diseases, Head and Neck Center, University of Helsinki and Helsinki University Hospital, Helsinki, Finland
4. Department of Dental Medicine, Division of Periodontology, Karolinska Institutet, Stockholm, Sweden