Efficacy of Etidronic Acid for Smear Layer Removal: A Systematic Review of In Vitro Studies

Irrigation plays a crucial role in the success of root canal treatment; however, currently, no standardized irrigation protocols exist, particularly regarding the optimal sequence for smear layer removal. This systematic review aimed to determine which irrigation protocol achieves superior smear layer removal: traditional sequential irrigation with sodium hypochlorite (NaOCl) followed by ethylenediaminetetraacetic acid (EDTA), or irrigation with etidronic acid, either combined with NaOCl in continuous chelation or used as a final irrigant. Continuous chelation with etidronic acid may be clinically advantageous in daily practice, as it would facilitate workflow by using a single irrigating solution without compromising the efficacy of the irrigation process. A comprehensive electronic search was conducted in Medline, Embase, Cochrane, Scopus, and Web of Science, last updated in August 2025. In vitro studies were selected according to predefined PICO-based criteria. Two reviewers independently screened the studies and extracted data, with an inter-rater agreement of 0.92 using the Kappa index. Risk of bias was evaluated using a modified CONSORT checklist for in vitro studies on dental materials. The average item compliance of the included studies was 58%. The maximum score was 73% and the minimum was 47%. Twenty studies met the inclusion criteria. Etidronic acid used in continuous chelation showed equal or superior smear layer removal compared with sequential irrigation in nine of ten studies. Conversely, when used as a final irrigant, etidronic acid demonstrated inferior performance in more than half of the studies, particularly in the apical third. Based on the available evidence, etidronic acid in continuous chelation appears as effective as, or more effective than, traditional NaOCl-EDTA sequential irrigation.