(1,688 words) June 2025.
Introduction
Biofilms are complex, surface-bound microbial communities encased in a self-produced matrix. In dental clinics, biofilms readily form wherever moisture and nutrients persist. Common habitats include:
- Equipment (dental unit waterlines (DUWL), operatory surfaces, instruments)
- Restorative materials (crowns & fillings)
- Dental prostheses (implants, dentures, bridges, crowns & veneers)
- Oral cavity (gum pockets, tooth surfaces & root canals, and implant surfaces
In DUWLs, microbial ‘cities’ arise because water stagnates in narrow tubing and tubing plastics foster attachment and promote rapid biofilm growth. Studies have found DUWL water with bacterial loads up to ~19,500 CFU/mL – vastly higher than normal drinking water– posing serious infection risks (Care Quality Commission, 2023). Patients’ mouths and surgical sites are exposed directly to these contaminants via a number of contact points, including water (chairs), air (aerosols) and cross infection (patient to patient).
Professional guidelines underline these dangers. ‘Best Practice’ in the UK’s HTM 01-05 requires a number of methods to control infection from water, including:
- Flushing at beginning and end of day, plus between patients to reduce planktonic microbes
- Antimicrobial in procedural water used in chair (continuous dosing) using a chemical)
- Periodic shock treatment to remove established biofilm.
The Care Quality Commission (CQC) similarly mandates written waterline management schemes and Legionella risk assessments for all practices (Care Quality Commission, 2023).
Likewise, periodontal biofilm (plaque) on teeth can fuel gingivitis and periodontitis if not controlled, and root canal biofilms threaten endodontic success unless eradicated (Aherne et al., 2022; Garcia et al., 2010). Contaminated impressions and casts can transfer pathogens to dental labs (Jasim and Abass, 2022).
In summary, dental biofilms jeopardize patient and staff safety – from routine dental water exposure to invasive procedures – unless rigorously managed. Consistent science-based infection control can keep dental biofilms – and their free-floating lanktonic bacteria – in check, but commonly used agents typically have limitations or associated risks that must be mitigated.
Comparative Analysis of Dental Disinfectants
Dentistry employs various antimicrobials against biofilms. The table below compares the major agents on efficacy, safety, environmental impact, and best-use scenarios using peer-reviewed studies. Key distinctions include penetrative power (biofilm disruption), toxicity, and spectrum.
| Agent | Antimicrobial Efficacy | Clinical Safety | Environmental Impact | Best Use in Dentistry |
|---|---|---|---|---|
| Quaternary Ammoniums (Quats) | Broad surface germicide; good against bacteria and enveloped viruses. Poor penetration of heavy biofilms and spores. | Generally non-corrosive; may irritate eyes/skin; can leave residues that select for resistant microbes. | Relatively persistent; can bioaccumulate; moderate aquatic toxicity. | Surface/equipment wipes DUWL flushing (some units) Not used in patient tissues or liquids. |
| Alcohol (EtOH/IPA) | Rapid kill of bacteria and most viruses on contact; no residual action; ineffective against spores and biofilms (evaporates quickly). | Rapid kill of bacteria and most viruses on contact; no residual action; ineffective against spores and biofilms (evaporates quickly). Safe for skin (though drying); flammable; inhalation of fumes can irritate. | Volatile organic solvent (VOCs) that evaporates (low long-term residue). | Hand hygiene sanitizer; surface disinfection wipes Not effective for deep biofilm or root canals. |
| Hydrogen Peroxide (H₂O₂) | Broad-spectrum oxidizer (bacteria, viruses, fungi, spores at ≥3%); moderate contact time. | Breaks down into water/O₂ (benign); can irritate mucosa and corrode metal at high concentrations. | Decomposes to water and oxygen – highly eco-friendly. | Surface disinfection (sprays/fogging). Some DUWL dosing. Possible adjunct irrigation/rinse at low conc. |
| Chlorhexidine (CHX) | Broad antibacterial (especially Gram+); strong substantivity on oral tissues. Limited effect on spores/viruses. | Safe at dental concentrations; causes tooth staining and taste changes; occasional mucosal irritation. | Moderately persistent in wastewater; some aquatic toxicity if concentrated. | Pre-/post-procedural oral rinse. Periodontal pocket irrigation/gels. Antimicrobial mouthwash. Not used on instruments or waterlines (stains and no cleaning action). |
| Sodium Hypochlorite (NaOCl) | Very broad (bacteria, viruses, fungi, spores); powerful oxidizer that dissolves tissue and biofilm matrix. Highly effective with short contact. | Highly caustic/toxic to tissues; can burn mucosa and skin; strong odour/fumes. Requires dilution. | Forms chlorinated byproducts; highly toxic to aquatic life if disposed improperly. | Endodontic irrigant (1–6% solutions) and surface soak. Laboratory disinfectant DUWL shock treatment (low conc). |
| Chlorine Dioxide (ClO₂) | Broad-spectrum oxidizer (bacteria, spores, viruses); effective at low concentrations; penetrates biofilms | Toxic/irritant gas at high levels; commercial use is in controlled concentration. | Breaks to chlorite/chlorate; byproducts require careful neutralization. | Tablet or gas-phase DUWL disinfection. Environmental spray/UV systems. Rarely used for patient rinses. |
| Stabilized Hypochlorous Acid (HOCl) | Broadest spectrum (bacteria, viruses, fungi, spores); neutral HOCl penetrates cells and biofilms >100× more potently than alkaline NaOCl. Rapid kill in minutes. | Endogenously produced by human immune cells – exceptionally safe. Non-staining; non-sensitizing; no toxic residues. | Breaks down to salt (NaCl) and water; essentially no ecological hazard. | DUWL continuous dose/shock. Surface/instrument spray Hand disinfectant Antimicrobial mouthwash Oral rinse for periodontal therapy Root canal irrigant (FDA-approved Aquatine EC). |
Stabilized Hypochlorous Acid: The New Gold Standard?
Stabilized HOCl is emerging as the most effective and least problematic dental disinfectant across all dental biofilm habitats. Unlike NaOCl bleach, HOCl is uncharged and of low molecular weight, so it penetrates and destroys biofilm bacteria more completely. Di Nardo et al. (2024) report that HOCl’s antibacterial activity can exceed NaOCl by orders of magnitude.
Aherne et al. (2022) showed that trace HOCl (5 ppm) eradicated mixed oral biofilms in minutes with zero enamel erosion or keratinocyte toxicity – an effect not seen with chlorhexidine. Similarly, Lin et al. (2023) noted that HOCl “removes the outer polymer matrix of biofilms” and provides broad, plaque-relevant antimicrobial action without staining or mucosal irritation.
HOCl’s safety is unmatched: it is naturally produced by white blood cells (neutrophils to be precise) during phagocytosis, the body’s natural response to attack.
Environmentally, HOCl breaks down into simple saline solution unlike quaternary ammoniums or bleach that leave harmful residues). HOCl has been shown to be non-cytotoxic to human cells in the effective antimicrobial concentration range (Lewandowski et al., 2024); also, non-irritating, non-sensitizing, and less cytotoxic to mammalian cells than NaOCl (Wang et al., 2007).
Recent developments now deliver stabilized HOCl in ready-to-use form with a shelf life up to two years (unlike onsite HOCl generators). Stabilized HOCl irrigants for treating gum pocket and root canal infections are new innovations that will be available to global dentistry very soon.
In periodontal therapy, HOCl rinses/gels have been shown to reduce pocket bacteria and inflammation. Lin et al. (2023) found that HOCl mouthwash halved salivary bacterial counts (including S. aureus) in periodontitis patients. In endodontics, HOCl has been FDA-approved as a water-soluble alternative irrigant which removes smear layer (Garcia et al., 2010), but without destroying the intertubular dentin, a problem associated with EDTA. HOCl irrigant can deliver benefits across multiple restorative treatments, including minimally invasive pulpotomy and pulpectomy, with superior antimicrobial agency and biofilm penetration.
For DUWLs, multiple studies show HOCl-based treatments eradicate existing biofilm and prevent re-formation. For example, Shajahan et al. (2016) found that an HOCl disinfectant left DUWL tubing walls “smooth with no biofilms,” whereas untreated lines were heavily colonized. HOCl has been successfully used by a number of the leading UK dental groups since 2016 for continuous and shock treatment for dental chair DUWLs.
As a surface and instrument disinfectant, HOCl sprays rapidly kill pathogens on operatory chairs and trays with no toxic residue, simplifying compliance. Even in the lab, HOCl is gentle: Jasim and Abass (2022) showed HOCl sprays preserved dental stone strength and detail better than bleach. Kadhim and Abass (2024) demonstrated that HOCl could even be incorporated into alginate impression material to self-disinfect during setting.
Stabilised HOCl: Aligning Practice with the Evidence
The clinical potential of HOCl as a dental biofilm agent has been recognised by the National Biofilm innovation Centre (NBIC) and its potential for supporting public health has been recognised by Innovate UK (UKRI).
In summary, emerging literature consistently elevates stabilized HOCl as the new gold standard for dental disinfection. Its unparalleled potency against biofilms, coupled with biocompatibility and low environmental impact, address the pitfalls of older agents. Given the robust evidence, new formulation of stabilised HOCl and forthcoming medical device innovations: adopting stabilized HOCl aligns practice with the science on biofilm control.
References (Harvard Style)
- Aherne, O., Ortiz, R., Fazli, M.M. and Davies, J.R., 2022. Effects of stabilized hypochlorous acid on oral biofilm bacteria.BMC Oral Health, 22, p.468. Available at: https://pubmed.ncbi.nlm.nih.gov/36275232/ [Accessed 3 Jun. 2025].
- Care Quality Commission, 2023.Dental mythbuster 5: Legionella and dental waterline management. Available at: https://www.cqc.org.uk [Accessed 3 Jun. 2025].
- Department of Health, 2013.HTM 01-05: Decontamination in primary care dental practices. London: Department of Health. Available at: https://www.england.nhs.uk [Accessed 3 Jun. 2025].
- Di Nardo, D., Capodiferro, S., Iorio-Siciliano, V. et al., 2024. A narrative review on the use of hypochlorous acid in dentistry.Annali di Stomatologia, 15(1), pp.34–40.
- Garcia, F.A., Murray, P.E., Garcia-Godoy, F. and Namerow, K.N., 2010. Effect of Aquatine Endodontic Cleanser (HOCl) on smear layer removal in root canals.Journal of Applied Oral Science, 18(4), pp.403–408.
- Jasim, Z.M. and Abass, S.M., 2022. The effect of hypochlorous acid disinfectant on the reproduction of details and surface hardness of type III dental stone. Cureus, 14(11), e32061.
- Kadhim, S.M. and Abass, S.M., 2024. Antimicrobial efficiency of hypochlorous acid incorporation and its effect on surface properties of irreversible hydrocolloid materials.Dentistry 3000, 12(2).
- Lewandowski, R.B., Stępińska, M., Osuchowski, Ł., Kasprzycka, W., Dobrzyńska, M., Mierczyk, Z. and Trafny, E.A., 2024. The HOCl dry fog—is it safe for human cells?PLOS ONE, 19(5), p.e0304602. Available at: https://doi.org/10.1371/journal.pone.0304602 [Accessed 3 Jun. 2025].
- Lin, Y.C., Yin, W.J. et al., 2023. Effects of hypochlorous acid mouthwash on salivary bacteria in periodontitis patients.BMC Oral Health, 23.
- Mehendale, F.V., Clayton, G., Homyer, K. and Reynolds, D.M., 2023. HOCl vs OCl–: clarification on chlorine-based disinfectants used within clinical settings.Journal of Global Health Reports, Article 84488.
- Shajahan, I.F., Kandaswamy, D., Padma Srikanth, Lakshmi Narayana, L. and Selvarajan, R., 2016. Dental unit waterlines disinfection using a hypochlorous acid–based disinfectant.Journal of Conservative Dentistry, 19(4), pp.347–350.
- Shajahan, I.F., Kandaswamy, D., Lakshminarayanan, L. and Selvarajan, R., 2017. Substantivity of a hypochlorous acid–based disinfectant against biofilm formation in dental unit waterlines.Journal of Conservative Dentistry, 20(1), pp.2–5.
- Walker, J.T. and Marsh, P.D., 2007. Microbial biofilm formation in DUWS and their control using disinfectants.Journal of Dentistry, 35(9), pp.721–730.
- Wang, L., et al., 2007. Cytotoxicity assessment of endodontic irrigants on human periodontal ligament cells.International Endodontic Journal, 40(10), pp.748–753.