Letters to the Editor

Pre-procedural mouthrinse to reduce SARS-CoV-2 viral load

As the current situation regarding the COVID-19 pandemic escalates rapidly all over the world, dental practitioners need to be equipped with up-to-date recommendations regarding effective measures to reduce aerosols during emergency dental procedures. Apart from the essential and enhanced measures, such as: high volume suction, personal protection (PPE), time and procedures for decontamination and between patients, it is also advised to apply a pre-procedural mouthrinse to minimize the viral load intra-orally. According to the launched first version of ‘Red Phase Guidance’ document, created by All Wales Clinical Dental Leads COVID-19 Group (March 2020), the hydrogen peroxide mouthrinse is suggested to reduce the amount of virus in the aerosol, however, it is not essential and evidence is not clear whether this advice should also cover the COVID case.¹ From the point of view of patients' health and safety, undoubtedly it could be a useful adjunct, as pre-operational antimicrobial mouthrinse is generally believed to reduce the number of oral microbiota. What is more, pre-procedural mouthrinse would be most useful when rubber dam cannot be applied.

Until now, limited evidence-based recommendations suggest that chlorhexidine gluconate, which is commonly used as a mouthwash in dental practice, may not be effective towards SARS-CoV-2.^2,3 It has been reported that, since SARS-CoV-2 is susceptible to the oxidation effect, ‘pre-procedural mouthrinse containing oxidative agents such as 1% hydrogen peroxide or 0.2% povidone is recommended, for the purpose of reducing the salivary load of micro-organisms, including potentially coronavirus SARS-CoV-2 carriage’.⁴ From a purely clinical point of view, iodine-based antiseptics are generally not recommended due to their potential side-effects, including severe hypersensitivity/allergy reactions. Interestingly, the recent Chinese Guideline for the Diagnosis and Treatment of Novel Coronavirus Pneumonia states that the virus is sensitive to ultraviolet and heat and exposure to 56°C for 30 minutes and lipid solvents such as ether, 75% ethanol, chlorine-containing disinfectant, and chloroform can effectively inactivate the virus.⁵ Chlorhexidine has not been effective in inactivating the virus,⁵ despite having a well known and evidence-based antimicrobial effect. Therefore the question arises, why this broad spectrum antibacterial, antifungal and antiviral agent appears not to be an optimal anti-SARS-CoV-2 agent? Evidence-based data elucidated that chlorhexidine mouthwash has been found significantly to increase the lactate-producing oral microbiota that can lower saliva pH, accompanied by a reduction of buffering capacity.⁶ What is more interesting is that low saliva pH can contribute to more potent intracellular viral invasion via an endocytic entry mechanism and low pH-dependent activation during entry into host cells.^7,8 The endocytic mechanism is believed to be a pH-sensitive process. However, mouthrinsing using some over-the-counter mouthwashes, such as those based on essential oils (eg Listerine), after an acidic challenge, increased salivary pH with a neutralizing effect.^9,10

Interestingly, it has been observed that essential oils exhibit inhibitory activity against SARS-CoV and HSV-1 replication in vitro.¹¹ In addition, avian (non-human) coronavirus responsible for infectious bronchitis in birds is susceptible to a mixture of essential oils and oleoresins from medicinal plants, exhibiting antiviral activity.¹² It is noteworthy that the antiviral efficacy of various essential oils is highly variable due to their chemical characteristics and not pre-eminent for all strains. Nevertheless, the mechanism of coronavirus virulence is undoubtedly complex, involving salivary defence molecules, oral mucosa barrier affinity/penetrability and immune response. Further investigations should, thus, focus on targeting specific viral strains and selected antimicrobial agents.

As the oxidative agents might not be available now, due to the global shortage of disinfectants and prioritization given to hospitals, dental practitioners would like to know what sort of additional measures might be utilized to minimize the exposure to risk. How about using, for example, chlorhexidine in higher concentrations, or other antiseptic agents, such as octenidine, cetilpiridine? Overall, taking into consideration the pH-dependent mechanism of host entry, the antiviral effectiveness of common antimicrobials seems to be associated with solution acidity. We are aware that we could get more common mouthwashes widely available, such as Peroxyl (Colgate), Crest 3D White (Crest) with a hydrogen peroxide ingredient, however, their range of standard 1–1.5% H₂O₂ concentration might be too low to be efficient towards a specific virus strain, including SARS-CoV-2. There is always an alternative option to use hydrogen peroxide mouthwash, with a right concentration arranged by a local pharmacy as per the BNP formulary. As dental practitioners, we urgently need more research-based information on how mouthwashes alter the balance of oral micro-organisms in the face of the recent COVID-19 outbreak, to protect our patients and staff.