Nonsurgical root canal retreatment may become essential when the initial endodontic treatment fails because of the persistent intracanal or extracanal infections.It has been stated that the one of the main cause of posttreatment disease is the persistent or reintroduced microorganism such as enterococcus faecalis. Supplementary disinfection techniques such as irrigation agitation methods can help elimination of bacteria from root canal systems.

The aim of this in vivo study was to compare the effect of passive ultrasonic irrigation, manual dynamic activation and photodynamic therapy in reducing bacterial load in endodontic retreatment cases with periradicular lesion by using polymerase chain reaction (PCR)in a single visit root canal treatment.

Thirty-six teeth with a single root and a single canal with posttreatment apical periodontitis which needed retreatment were selected for this study. Teeth were randomly divided into 3 groups according to the supplementary disinfection techniques used: Passive ultrasonic irrigation, Manual dynamic activation and Photodynamic therapy. Microbiological samples were taken before any intervention, after conventional chemo-mechanical preparation, and after disinfection techniques with sterile paper points and held in thioglycollate broth, and then were transferred to the microbiological laboratory. The amounts of e.faecalis in these samples was measured by using PCR.

Inclusion Criteria:

Patients with no clinical symptoms Endodontically treated teeth Single rooted teeth

Exclusion Criteria:

Teeth with fractured instrument, resorption, perforation, ledge, over fillings Periodontal pockets deeper than 4 mm