Study population Study subjects were recruited consecutively from patients treated by dental specialists in periodontology or implantology in Germany (University of Bonn), the Netherlands (Amsterdam), Italy (Rome University), Spain (University Madrid) and Sweden (Kristianstad University). Each participant signed an informed consent in accordance with the Helsinki Declaration of 1975 as revised in 2008. The Ethical Committee for human subject trials in each institution approved the study protocol individually. Seventy informed and consenting patients above the age of 18 years of age with a diagnosis of peri-implantitis were enrolled in the study and surgery was performed.