In prosthodontic rehabilitation after tooth loss the therapy with dental implants is increasing and the duration rate is up to 15 years and more. Therefore, more patients have a risk of developing a peri-implant infection, such as mucositis or peri-implantitis. The prevalence is described as being 12-43 % after functional loading. These situations may influence the long-term stability and in a worst case scenario an implant failure will result. The knowledge of risk factors as well as the diagnostic tools and the appropriate therapy is important for finding a solution.