Photodynamic therapy (PDT) has emerged as a novel, noninvasive photochemical disinfection therapeutic approach to treat cancer, infections, and diseases IN MEDICAL and dental fields. It includes the use of a low-power diode laser in combination with photosensitizing compounds. The photosensitizer binds to the target cells and when it is irradiated with light of specific wavelength, in the presence of oxygen, it undergoes a transition from a low-energy ground state to an excited singlet state; then singlet oxygen and other very reactive agents are produced, which are toxic to these target cells Antimicrobial PDT (aPDT) seems to be a emerging unique and interesting therapeutic approach and holds promise as a substitute for currently available chemotherapy in the treatment of periodontal and peri-implant diseases.