Purpose: This study aimed to evaluate the treatment outcome after using diode laser disinfection of root canals in necrotic teeth with periapical radiolucency. Subjects and Methods: Thirty patients of age range between 20 and 50 years old were involved in this study. They were divided randomly into two groups (15 teeth each). Group I: Access cavity preparation was performed and microbiological sample (SI1) was taken. The root canal was prepared using ProTaper rotary instruments up to #F4 and irrigated with 2ml of 2.6% sodium hypochlorite, this was repeated after each instrument use with total volume 14ml. Smear layer removal with 17% EDTA (5ml) was performed, saline solution (5ml) was used as a final irrigant then, the canal was irradiated with 810 nm diode laser in a continuous wave mode with a power of 1.5 w then, microbiological sample (SI2) was taken. Group II: The same steps were followed as in group I up to the
use of saline solution (5ml) as a final irrigant, then microbiological sample (SII2) was taken. The treatment outcome was evaluated clinically (pain recording using Visual Analogue Scale (VAS) at 6,12,24,48 and 72hours) and microbiologically (reduction in number of CFU of microorganisms). Results: There was no statistically significant difference between pain scores in the two groups. Group I showed statistically significant higher mean percentage reduction in bacterial and fungal counts than group II. Conclusion: 810 nm diode laser can be used as an adjunct to conventional root canal treatment in necrotic teeth with periapical radiolucency.