Effect of Diode Laser and Sodium Hypochlorite (NaOCl) on E. faecalis in Infected Root Canals of Permanent Teeth: An In Vitro Comparative Study

BackgroundEndodontic therapy requires effective disinfection of dentinal tubules to prevent treatment failure.Enterococcus faecalis (E.faecalis) is a resilient pathogen that penetrates dentin and resists conventional irrigants.Sodium hypochlorite (NaOCl) is widely used but has limited penetration into the tubules.Diode lasers offer deeper antimicrobial action, yet evidence at 980 nm remains limited. AimTo compare the antimicrobial effect of 980 nm diode laser and NaOCl on E. faecalis in infected root canals of permanent teeth in vitro. Materials and methodsFifty-five extracted permanent mandibular single-rooted premolars were standardized, sterilized, instrumented, and inoculated with E. faecalis.After 14 days of incubation, specimens were randomly allocated into five groups (n=11): Group A: NaOCl, Group B: saline, Group C: diode laser, Group D: diode laser with NaOCl, Group E: NaOCl with diode laser.Residual NaOCl was neutralized with 5% sodium thiosulfate.Post-treatment E. faecalis counts were recorded in each group and compared.Viable bacterial counts were determined by colony-forming units (CFU) analysis and expressed as log₁₀ CFU/mL.Data were analyzed using SPSS (IBM Corp., Armonk, USA).One-way analysis of variance (ANOVA) followed by Tukey's honestly significant difference (HSD) post hoc test was used to evaluate the statistical differences among the five groups. ResultBacterial counts differed significantly among the five groups (p<0.001).Relative to saline, NaOCl alone lowered the mean count by 20.8% (p<0.001),whereas diode laser alone did not differ significantly from saline (4.5% reduction).Both combination protocols demonstrated significantly lower post-treatment counts than either treatment alone, with diode laser followed by NaOCl achieving the lowest count (50.5% lower than saline) and differing significantly from the reverse sequence (28.5% lower than saline; p<0.001). ConclusionWithin the limitations of this in vitro study, in which pre-treatment bacterial counts were not recorded, combining NaOCl with 980-nm diode laser irradiation resulted in lower post-treatment E. faecalis counts than either agent alone.Diode laser followed by NaOCl gave the lowest counts and differed significantly from the reverse sequence.