Periodontitis is a multifactorial disease that is associated with loss of the supporting tissues around the tooth. A major objective of periodontal therapy is to remove soft and hard, supragingival and subgingival deposits from the root surface to stop disease progression. Although non–surgical periodontal treatment may result in significant clinical improvements, none of the currently available instrumentation techniques are effective in completely eliminating subgingival bacteria and calculus. Photodynamic therapy is a new type of non–invasive phototherapy for bacterial elimination, which uses low–level laser light and selectively targets the bacteria without potentially damaging the host tissues.