To evaluate the additional effect of a single session of antimicrobial photodynamic therapy (aPDT) on the tongue as an adjunct to scaling and root planing (SRP) on most common volatile sulfur-producing microbes such as Porphyromonas gingivalis (Pg), Treponema denticola (Td) and Fusobacterium nucleatum (Fn) on 3rd, 7th and 14th day postoperatively using RT-PCR analysis.