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.