In Germany, more than 1 million dental implants are placed each year. Often this is done as a replacement for teeth that have been lost due to periodontal disease. However, an inflammation at the implant can occur even a long time after successful healing. This so-called peri-implantitis has many features in common with periodontitis. It is also a multifactorial disease triggered by several risk factors, especially by the presence of certain bacteria. However, the peri-implant tissue has special structures that allow the bacteria to progress rapidly into deeper layers.