1. Department of Preventive Dentistry, Periodontology and Implant Biology Dental School, Aristotle University of Thessaloniki Thessaloniki Greece
2. 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. Division of Periodontology, Department of Dental Medicine Karolinska Institutet Stockholm Sweden