Introduction.  The treatment of chronic apical periodontitis remains a relevant issue in dentistry.    A key stage of endodontic treatment is the removal of the smear layer (SL), which forms during mechanical root canal instrumentation and prevents adequate disinfection. Traditional chelating agents, such as EDTA, have limited effectiveness in the apical third and may damage dentin. Etidronic acid (HEBP) is considered a promising alternative, as it allows continuous chelation simultaneously with antiseptic irrigation.    Aim.  To evaluate the effectiveness of smear layer removal in the root canal using various chelating agents according to in vitro studies.    Materials and methods.  A literature review was conducted in the Scopus, PubMed, Web of Science, eLIBRARY.RU, and Google databases for the period 2015–2025 using the following keywords: HEBP, EDTA, etidronate, smear layer, in vitro study. Out of 1,218 identified publications, after excluding duplicates, reviews, clinical cases, and studies with non uniform irrigant activation, 23 full text articles were selected for analysis.    Results. EDTA is effective in the coronal and middle thirds but removes the smear layer less effectively in the apical part. Activation (ultrasonic, sonic) improves its performance; however, the risk of reduced dentin strength remains. HEBP, especially in combination with sodium hypochlorite, provides stable smear layer removal throughout the entire canal, including the apical third, and prevents debris accumulation. At the same time, HEBP solutions are less effective in dissolving pulp compared to pure hypochlorite.    Conclusions. HEBP in a continuous chelation protocol has advantages over EDTA in terms of cleaning uniformity and dentin safety, but it requires consideration of its impact on the organic tissue dissolution ability of sodium hypochlorite.

Background: 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. Methods: 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. Results: 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. Conclusions: Continuous chelation with etidronate in 3% sodium hypochlorite showed promising antimicrobial performance and may represent a clinically feasible alternative irrigation strategy.