Aim: This in vitro study compared the efficacy of Er,Cr:YSGG laser (2780 nm), diode laser (976 nm), passive ultrasonic irrigation (PUI), and conventional syringe irrigation (CSI) in removing smear layer from root canals, evaluating the influence of irrigant chemistry (NaOCl+EDTA, EDTA, NaOCl, saline) and root canal level (coronal, middle, apical). Materials & Methods: One hundred sixty single-rooted premolars were instrumented and randomly divided into four irrigation groups (n=40/group), Er,Cr:YSGG (25 mJ, 50 Hz) using radial-firing tip; diode laser (CW, 1.5 W); PUI; and CNI side-vented needle. They further subdivided by irrigant (n=10/subgroup). Irrigation was performed in four 15-second cycles. Smear layer removal was scored (1–5) via SEM by blinded evaluators. Data were analyzed using Kruskal-Wallis and Mann-Whitney tests (p ≤ 0.05). Results: Er,Cr:YSGG achieved the lowest scores (optimal cleaning) across all thirds (1.2–2.7), outperforming diode laser (1.7–3.4), PUI (2.3–4.4), and CNI (2.4–4.7) (p < 0.001). NaOCl+EDTA was most effective (p < 0.05), though saline with Er,Cr:YSGG surpassed NaOCl alone. Apical thirds consistently showed poorer removal (p < 0.001). Conclusion: Er,Cr:YSGG laser activation with NaOCl+EDTA is the most effective protocol for smear layer removal. Mechanical effects of Er,Cr:YSGG dominated with saline. Diode laser activation surpassed PUI.
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