Impact of Smear Layer Removal Using Etidronate- and EDTA-Based Irrigation Protocols on Root Canal Microbiota: An In Vivo Study

<b>Background</b>: The effective elimination of root canal microbiota is essential for the treatment of apical periodontitis. The smear layer formed during instrumentation limits the penetration of irrigants into dentinal tubules, making chelation a critical component of irrigation protocols. While ethylenediaminetetraacetic acid (EDTA) is commonly used for smear layer removal, etidronate has been proposed as an alternative due to its chemical compatibility with sodium hypochlorite. The aim of this study was to compare the effectiveness of different irrigation protocols in eliminating microorganisms from the root canal system in patients with chronic apical periodontitis. <b>Methods</b>: Thirty patients aged 18-44 years diagnosed with chronic apical periodontitis (ICD-10 code K04.5) were included. Three irrigation protocols were evaluated: (1) 3% sodium hypochlorite followed by 17% EDTA; (2) 3% sodium hypochlorite followed by a 9% aqueous solution of etidronate; and (3) a 9% solution of etidronate dissolved in 3% sodium hypochlorite (continuous chelation). Microbiological samples were collected before and after root canal instrumentation and irrigation. Microbial analysis was performed using gas chromatography-mass spectrometry. <b>Results</b>: All protocols resulted in a reduction in microbial load. However, protocols using 3% sodium hypochlorite with 17% EDTA and continuous chelation with etidronate in sodium hypochlorite demonstrated a greater number of statistically significant reductions. Sequential irrigation with aqueous etidronate showed the lowest antimicrobial effectiveness. <b>Conclusions</b>: Continuous chelation with etidronate in 3% sodium hypochlorite showed promising antimicrobial performance and may represent a clinically feasible alternative irrigation strategy.