Treatment of existing periodontitis performed before recruitment. Baseline examination including samples of microbiota and peri-implant fluid followed by surgical treatment. Access surgery to remove chronic inflammatory tissue and clean the implant surface from biofilm and implant stone with hand instrument and ultrasonic device with special tips for implants, followed by polishing the implant surface with a gauze, super floss and rinsing with saline. Allocation with a performed block randomisation at the stage of surgery, after cleaning of implant surface. Application of enamel matrix derivative (Emdogain®) or not, just before closure of flap. After surgery rinsing with chlorhexidine 0.2% twice a day in 6 weeks. No systemic antibiotic used in this study.