For decades, the central challenge in endodontic irrigation has been finding a way to eliminate biofilms and infected tissue without compromising patient safety. Sodium hypochlorite (NaOCl) has long dominated clinical protocols because its ability to dissolve necrotic tissue and disrupt complex biofilms remains unparalleled among currently available irrigants (Zehnder, 2006).
Its role is particularly indispensable in necrotic canals and large periapical lesions, where histological evidence shows intraradicular biofilms in roughly 77% of cases, with biofilm presence correlating strongly with lesion size (Ricucci & Siqueira, 2010) .
Yet as endodontics shifts toward vital pulp preservation, minimally invasive endodontics, and biologically respectful care, the limitations of NaOCl—its cytotoxicity, potential to weaken dentine, interference with bonding, and the well-documented, though uncommon, risk of severe extrusion injuries—seem increasingly out of alignment with the field’s therapeutic aspirations (Hsieh et al., 2020; Pai et al., 2025) .
These challenges do not diminish NaOCl’s necessity in necrotic cases, but they do highlight the need for more nuanced irrigation strategies that match irrigant chemistry to clinical intent, especially when the goal is to retain rather than remove vital tissue.
Stabilised hypochlorous acid – a novel disinfectant agent for dentistry
Stabilised hypochlorous acid (HOCl), the same oxidant produced by neutrophils during host immune defence, is emerging as the most promising candidate to fill this need. With US FDA medical device approval for endodontic use anticipated in late 2026 and EU Class III approval projected for mid-2027, clinicians may soon gain regulated access to a new irrigant category: a broad-spectrum oxidant with significantly better biocompatibility than NaOCl or chlorhexidine (CHX), and the potential to be used in far higher volumes without damaging oral soft tissues or dentine.
HOCl’s antimicrobial mechanism is well established in medical literature and increasingly supported in dental studies. It exhibits rapid, broad-spectrum antimicrobial action, with documented efficacy against biofilm-forming and drug-resistant organisms in both in-vitro and in-vivo contexts (Boecker et al., 2023) .
Its cytocompatibility profile is particularly noteworthy: multiple studies show HOCl causing substantially less damage to fibroblasts, epithelial cells, and pulp-relevant cell lines than NaOCl or CHX across comparable exposure windows (Bilvinaitė et al., 2022; Dallepiane et al., 2024) .
This makes HOCl inherently attractive in clinical scenarios where the priority is not tissue dissolution but rather the preservation of viable cells, such as vital pulp therapy (VPT), regenerative procedures, traumatic injuries with open apices, and cases where even low-grade extrusion would pose unacceptable risks.
Further strengthening the case for HOCl is its demonstrated ability to assist in smear layer and debris removal when paired with EDTA. Ex vivo research shows that HOCl-based solutions can achieve effective smear removal—comparable to NaOCl+EDTA combinations—in human teeth models (Garcia et al., 2010; Bilvinaitė et al., 2022). Its cleaning performance in final-rinse roles is also promising. Importantly, because HOCl is not caustic to vital tissues, it enables high-volume irrigation, providing an advantage in complex anatomies where irrigant exchange and penetration matter.
Several papers emphasise that HOCl’s low toxicity—particularly toward fibroblasts and stem-cell–rich tissues—extends its suitability to patient groups where harsher oxidants are contraindicated. Paediatric endodontic data further reinforce its safety: oxidative potential HOCl-based water performed comparably to 1% NaOCl in primary teeth with necrotic pulps (Valdez-González et al., 2012) , suggesting tolerability in clinical environments where tissue preservation is paramount.
Safer Endo Irrigation on the Horizon
This combination of antimicrobial potency, biocompatibility, and cleaning potential positions HOCl particularly well within modern endodontic workflows.
In VPT and minimally invasive endodontics, irrigation must be powerful enough to reduce microbial bioburden yet gentle enough to avoid harming surviving pulp tissue. The American Association of Endodontists (AAE) underscores that irrigants used in VPT must disinfect without compromising pulp vitality (AAE, 2021). HOCl aligns closely with this requirement, offering adequate antimicrobial action without the structural or cellular damage associated with NaOCl.
As clinical evidence accumulates—such as Asgary et al. (2022), which demonstrated that pulpotomy can rival full root-canal therapy in mature permanent teeth—it becomes increasingly clear that irrigants must support, not undermine, tissue viability in situations where vitality can be maintained.
HOCl also appears well suited to the role of final irrigant in conventional root-canal therapy. A widely discussed emerging protocol involves using NaOCl and EDTA for the core chemomechanical phase, followed by HOCl as the final rinse. This sequence leverages NaOCl’s dissolution capability while exploiting HOCl’s superior cytocompatibility and its demonstrated smear-removal contribution (Bilvinaitė et al., 2022).
HOCl’s gentler chemistry also makes it a safer choice in anatomies with high extrusion risk—immature apices, wide foramina, or situations involving compromised periapical tissues—where NaOCl accidents carry serious consequences. In vivo studies comparing HOCl-based electrolyzed oxidizing water with NaOCl demonstrate clear advantages in tissue tolerability (Hsieh et al., 2020), further supporting this role.
Does stabilised HOCl spell the end for CHX in Endo?
By contrast, the position of CHX as an endodontic irrigant continues to weaken. The limitations of CHX are consistent across the literature. It cannot dissolve organic tissue, rendering it ineffective for smear or debris removal (Zehnder, 2006). Its cytotoxicity at endodontic concentrations is significant, with multiple cell-viability studies demonstrating greater toxicity than HOCl. CHX is also chemically incompatible with NaOCl, requiring intermediate rinses to prevent precipitate formation—adding complexity to irrigation workflows.
Although CHX is often cited for its antimicrobial substantivity, this benefit does not compensate for its reduced efficacy in dentinal tubules and limited impact on inorganic smear. In contrast, HOCl offers broader antimicrobial efficacy (Boecker et al., 2023) with lower cytotoxicity (Bilvinaitė et al., 2022), and effective smear removal when paired with EDTA. CHX therefore provides no meaningful advantage over HOCl in biologically oriented endodontic practice.
What next for Hypochlorous Acid in Endo?
Despite its promise, HOCl is not a substitute for NaOCl in every situation and the current evidence base, while encouraging, also highlights some gaps, many of which are currently in research.
Standardisation of activation parameters—ultrasonic, sonic, or multisonic—remains undeveloped, and detailed analyses of HOCl interactions with bioceramics, calcium-silicate cements, and resin-based materials are essential before full integration into all clinical protocols. Adult clinical outcome trials comparing HOCl–EDTA to NaOCl–EDTA sequences will deliver the final piece of the puzzle.
Nevertheless, the direction of travel is clear. If regulatory timelines hold, stabilised HOCl will become an approved Class III irrigant in the EU & US by end of-2026.
Based on current evidence, its most compelling roles will include serving as the first-line irrigant for vital pulp therapy and minimally invasive care, as a safer and more biocompatible final rinse in RCT, as the preferred alternative to CHX, and as an adjunct that allows clinicians to reserve NaOCl only for cases requiring heavy organic dissolution.
This is not about discarding NaOCl; it is about using irrigants more selectively and intelligently, matching chemistry to biology. Endodontics is moving toward a future defined by precision, preservation, and patient-centred safety. HOCl is not merely another irrigant—it represents a shift toward a new philosophy of care, one that supports healing rather than compromising it.