Periodontitis are infectious and inflammatory diseases of gum and tooth supporting tissues leading to tooth loss and oral disability. Twenty to 30 percents of patients treated for periodontal diseases display more or less pronounced persistence of periodontal tissue infection, inflammation, and destruction. The therapeutic additional value of photodynamic anti-infectious treatment remains controversial. The objective of this study is to evaluate the mid-term effect of the photodynamic device Fotosan®630 on severe periodontitis treatment outcomes and to define its specific therapeutic indications.