Essential Oil Mouthwash - Oral Hygiene

Background The application of mouthwash that decreases viral load in the oral cavity has been reported to be effective in mitigating disease severity, as evidenced by reductions in the length of hospital stays, the need for intensive care admission, and mortality rates (da Silva Santos et al., 2021). While bacteria naturally inhabit the oral cavity, certain bacterial species are responsible for the development of caries and periodontal disease, particularly prevalent among the elderly in the community (Filipovic et al., 2020). Available antimicrobial mouthwashes can either eliminate pathogenic bacteria (bactericidal) or inhibit their growth (bacteriostatic). Additionally, some formulations prevent the development of biofilms, which play a crucial role in the formation of plaque and the progression of dental caries, gingivitis, and periodontal disease (Brookes et al., 2023). The anti-plaque activity of mouthwashes is partly attributed to their antimicrobial properties, with key antiseptic ingredients including chlorhexidine (CHX) and essential oils (Liu et al., 2023). Specifically, chlorhexidine or essential oils formulations can penetrate bacterial biofilms and exert potent antibacterial effects (Ramberg et al., 2016). Additionally, antiseptic mouthwashes complement daily brushing in managing dental plaque and gingivitis (Navabi et al., 2024).

A wide range of chemical and natural antiseptic mouthwashes is readily available over-the-counter (OTC) for managing bad breath (halitosis), dental decay, and gum disease. These products are often used daily without requiring a prescription or guidance from a dental professional. Common active ingredients include chlorhexidine (CHX), hydrogen peroxide (H2O2), cetylpyridinium chloride (CPC), povidone-iodine (PVP-I), and essential oils (EO) (Brookes et al., 2023). Chlorhexidine (CHX) has demonstrated antiviral properties in vitro against specific viruses, including herpes simplex type-1, influenza A, human coronavirus, and severe acute respiratory syndrome-related coronavirus. It appears to be more effective against enveloped viruses than non-enveloped ones (Brookes et al., 2023). Substantial evidence supports the antibacterial effects of oral rinses containing chlorhexidine (CHX) gluconate, significantly reducing bacterial populations on buccal epithelia and pellicles. These rinses are effective against various microorganisms, including Actinomyces naeslundii, Veillonella dispar, Prevotella nigrescens, and Streptococcus species (Babu \& Garcia-Godoy, 2014; Filipovic et al., 2020). Systematic reviews provide robust evidence indicating that commonly used mouthwashes effectively reduce plaque and gingivitis, with chlorhexidine (CHX) widely regarded as the most effective option (Brookes et al., 2023). Beyond its dental applications, CHX mouthwash has also been suggested to lower the risk of ventilator-associated pneumonia in critically ill patients (Hua et al., 2016). The effects of CHX mouthwash on bacterial species have been investigated through studies using in vitro oral microbial communities. For example, when a community of ten oral bacterial species was exposed to CHX, there were notable reductions in Prevotella sp. and Selenomonas infelix. In contrast, other species exhibited less pronounced reductions (McBain et al., 2003). The impact of Listerine® (LIS) on bacterial species has also been assessed using culture-based methods to quantify bacterial levels. One study reported significant reductions in Veillonella sp., Capnocytophaga sp., and Fusobacterium nucleatum in subgingival plaque after two weeks of gargling with LIS (Fine et al., 2007). In another in vitro study involving 40 oral bacterial species, CHX mouthwash was more effective than LIS in reducing all the species tested (Haffajee et al., 2008).

A systematic review revealed that alcohol-free povidone-iodine (PVP-I) mouthwash exhibits significant virucidal activity against SARS-CoV-2 in saliva at concentrations of 0.5% to 1%. However, a 2% concentration did not significantly reduce salivary viral load in one of the included studies. In clinical settings, a 30- to 60-second rinse with 0.5% or 1% PVP-I mouthwash before procedures may effectively reduce the risk of cross-infection, particularly during aerosol-generating procedures (AGPs) involving confirmed, suspected, or asymptomatic COVID-19 patients (Garcia-Sanchez et al., 2022). Povidone-iodine is commonly incorporated into mouthwashes at concentrations of 0.5% to 1.0% and is frequently recommended as a gargle for sore throats due to its potent antiseptic properties. It has demonstrated bactericidal, fungicidal, and virucidal efficacy and is extensively utilized for disinfecting skin and mucous membranes, such as in Betadine products. Beyond oral care, povidone-iodine is used in hand washes, surgical scrubs, and skin disinfectants at concentrations of 7.5% to 10% (Brookes et al., 2023; Stewart, 2022). Its broad-spectrum antimicrobial activity extends to oral microorganisms, including periodontal pathogens, fungi, mycobacteria, viruses, and protozoa, without exhibiting cytotoxic effects on human cells (Schreier et al., 1997). For decades, povidone-iodine mouthwash has been recommended for periodontal site decontamination before invasive procedures to reduce the risk of bacteremia (Brookes et al., 2023).

Essential oils (EOs) are natural extracts derived from various plants. They are recognized for their antibacterial, antifungal, and antioxidant properties, combined with relatively low toxicity (Brookes et al., 2023). Historically, essential oils have been used to enhance physical health, improve appearance, and protect the body from environmental damage. These versatile products serve multiple purposes, such as cleansing, perfuming, altering appearance, correcting body odors, and preserving or maintaining treated areas in optimal condition (Carvalho et al., 2016). Essential oils and their compounds are commonly

optimal condition (Carvalho et al., 2016). Essential oils and their compounds are commonly incorporated into mouthwashes, primarily for their fragrance. However, evidence supporting their antibacterial efficacy against oral microbiota or their use as preservatives remains limited. For instance, benzyl alcohol is used mainly for fragrance and preservation, while its derivative, 2,4-dichlorobenzyl alcohol, is a mild antiseptic for oral and throat applications. Compounds such as limonene, linalool, citral, and cinnamaldehyde have demonstrated significant activity against oral pathogens, with geraniol and anethole showing some antimicrobial potential (Radzki et al., 2022). This systematic review presents the first comprehensive analysis of human trials assessing tea tree oil's therapeutic efficacy and safety. Tea tree oil's therapeutic applications span various medical fields, including dentistry, dermatology, infectious diseases, ophthalmology, and podiatry (Kairey et al., 2023). Listerine® (LIS), a widely used mouthwash containing four plant-derived essential oils-eucalyptol, menthol, methyl salicylate, and thymol-has been proven effective in reducing plaque and gingivitis (Alshehri, 2018). In this study, the selection criteria for essential oils included in mouthwash formulations were based on three key factors: 1) commercial availability, 2) antimicrobial efficacy against harmful anaerobic oral microorganisms, and 3) minimal toxicity to gingival cells.