Effect of 980 nm diode laser irradiation in comparison with conventional irrigation on smear layer removal from radicular dentin—an in vitro experimental study

Introduction: The smear layer in radicular dentin reduces effective disinfection by occluding dentinal tubules and decreasing dentin permeability, contributing to persistent microbial infection and root canal treatment failures. Objective: To compare the effect of 980 nm Diode laser irradiation and conventional irrigation with Sodium hypochlorite and ethylenediaminetetraacetic acid (NaOCl +EDTA) on smear layer removal in radicular dentin through dye penetration test. Material and methods: Sixty-six extracted single-rooted permanent teeth were randomly allocated into two groups. Group I underwent 980 nm diode laser irradiation using a 200 µm fiber in helicoidal motion (2 W power, 200 Hz frequency, 1–4 ms pulse duration). Group II received conventional irrigation with 3% NaOCl followed by 17% EDTA. All specimens were immersed in 2% methylene blue dye for 48 h, after which cross-sections were obtained at 3, 5, and 8 mm from the anatomical apex. Dye penetration diameter (mm) and area (mm²) between the inner and outer circumferences were measured using ImageJ software under a stereomicroscope. Statistical analysis was performed using one-way ANOVA with Bonferroni post-hoc tests. Results: The diode laser irradiation demonstrated overall significantly greater dentinal tubule penetration (16.2 ± 1.91 mm) compared to the conventional irrigation (5.32 ± 0.70 mm; p = 0.001). The overall mean area of the laser group (12.61 ± 2.02 mm²) was greater as compared to the conventional group (1.67 ± 0.73 mm²; p = 0.001). Conclusion: Diode laser irradiation may serve as an effective adjunct for smear layer removal and improved root canal disinfection.