In dentistry, dental implant applications for tooth loss/deficiency are prominent and provide successful long-term results in terms of functionality and aesthetics. However, peri-implant diseases such as peri-implant mucositis and peri-implantitis may develop due to biofilm accumulation around the implant. In peri-implantitis, in addition to the clinical inflammation findings seen in peri-implant mucositis, there is also progressive bone loss. This condition is to be treated with non-surgical or surgical methods. Titanium curettes, ultrasonic instruments, laser systems, and chitosan brushes are used for biofilm removal in non-surgical treatment. Chitosan is a natural polysaccharide obtained from chitin. It is biocompatible, biodegradable, and has antibacterial activity. In addition, chitosan reduces the levels of IL-1β, IL-6, and TNF-α, which also play a role in the pathogenesis of peri-implantitis, and exhibits anti-inflammatory effects on macrophages activated by lipopolysaccharide. Although many methods are used to treat peri-implantitis, successful and predictable results cannot be obtained. This study aims to examine the clinical and immunological findings and observe the changes in the non-surgical treatment of peri-implantitis using chitosan brush or titanium curette over 12 months. Sixty dental implants diagnosed with peri-implantitis clinically and radiographically at the Department of Periodontics, Faculty of Dentistry, Hacettepe University will be included in the study. Non-surgical peri-implantitis treatment of these patients will be performed using a chitosan brush (N=30, case group) or titanium curette (N=30, control group). Pre-operative and post-operative 3rd, 6th, and 12th months, clinical periodontal indices will be recorded, peri-implant crevicular fluid (PIF) will be collected, and maintenance treatment will be applied to the patients. IL-1β, TNF-α, IL-8, IL-10, and IL-17 levels in the collected PIF will be determined by the ELISA method. The effectiveness of chitosan brush and titanium curette in treating peri-implantitis will be evaluated and compared clinically and immunologically.