The purpose of this in vitro study was to investigate how sequential versus continuous chelation affects the removal of the smear layer and the hardness of root canal dentin, and to evaluate the influence of different agitation methods. Sixty-four palatal roots of maxillary first molars were prepared to size X3 using Protaper Next files. Samples were divided into two irrigation protocols: sequential chelation (SC) with 3% NaOCl followed by 17% EDTA, and continuous chelation (CC) using a dual-rinse solution (3% NaOCl/9% HEDP). Each protocol was further subdivided according to agitation technique: conventional needle (CN), EndoActivator (EA), ultrasonic (UAI), and Er.Cr.YSGG 2780 nm laser (n = 8 per subgroup). Smear layer removal was evaluated by scanning electron microscopy (SEM), and Vickers microhardness measurements were taken at depths of 50 and 100 µm. Statistical analysis included Kruskal–Wallis, Wilcoxon, and Mann–Whitney U tests, with significance set at p < 0.05.
Continuous chelation with ultrasonic or laser activation resulted in greater smear layer reduction in the apical and coronal regions, respectively, compared to sequential chelation (p < 0.05). No notable differences between SC and CC were observed for conventional needle or EndoActivator groups (p > 0.05). Overall, CC preserved dentin microhardness better than SC, with the exception of specific sections in CN, EA, and UAI groups at certain depths. Continuous chelation provides similar efficacy in smear layer removal as sequential chelation, while exerting a less negative effect on dentin microhardness.
