**9.7 Photodynamic therapy**

Photodynamic therapy has to be considered as an additional treatment option in peri-implantitis. Photodynamic therapy generates reactive oxygen species by multiplicity with help of a high-energy single-frequency light in combination with photosensitizers. In a wavelength range of 580–1400 nm and toluidine blue-concentrations between 10 and 50 μg/mL, photodynamic therapy generates bactericide effects against aerobic and anaerobic bacteria such as *Aggregatibacter actinomycetemcomitans*, *Porphyromonas gingivalis*, *Prevotella intermedia*, *Streptococcus mutans*, *Enterococcus faecalis* [86, 87]. An improvement in both clinical attachment and the bleeding index was observed on a moderate and severe peri-implantitis with phototherapy [88]. Photodynamic therapy has been tried as an adjunctive to manual debridement and local chemotherapeutic agents [89].
