Mohammad Asnaashari
Mostafa Godiny
Saranaz Azari-Marhabi
Fahimeh Sadat Tabatabaei
Maryam Barati

Abstract Introduction: The aim of this study was to compare the antibacterial efficacy of diode laser ۸۱۰nm and photodynamic therapy (PDT) in reducing bacterial microflora in endodontic retreatment of teeth with periradicular lesion.Methods: In this in vivo clinical trial, ۲۰ patients who needed endodontic retreatment were selected. After conventional chemo mechanical preparation of root canals, microbiological samples were taken with sterile paper point (PP), held in thioglycollate broth, and then were transferred to the microbiological lab. In the first group, PDT with methylene blue (MB) and diode laser (۸۱۰ nm, ۰.۲ W, ۴۰ seconds) was performed and in the second group diode laser (۸۱۰ nm, ۱.۲ W, ۳۰ seconds) was irradiated. Then second samples were taken from all canals.Results: CFU/ml amounts showed statistically significant reduction in both groups (P < ۰.۰۰۱). CFU/ml amounts were compared between the two groups and there was no statistical difference.Conclusion: PDT and diode laser ۸۱۰ nm irradiation are effective methods for root canal disinfection. PDT is a suitable alternative for diode laser ۸۱۰ nm irradiation, because of lower thermal risk on root dentin. Keywords: Endodontic Diode laser PDT.