The Use of Mouthrinses in the Fight Against Cariogenic Bacteria

Dental caries is a disease in which bacteria ferment carbohydrates, which produces acids and breaks down tooth mineral.^1,2 These cariogenic bacteria are acidogenic (acid-forming) and aciduric (tolerate a highly acidic environment), and include Streptococcus mutans, Streptococcus sobrinus, and lactobacilli.^3–5 The removal of plaque and reduction of cariogenic bacteria are key to preventing tooth decay. Mouthrinses are an important adjunct to reducing cariogenic bacteria in the oral cavity, secondary to the mechanical removal of plaque through toothbrushing and interproximal cleaning.

CARIOGENIC BACTERIA

Reducing cariogenic bacteria is integral to maintaining oral health. S. mutans—which describes seven streptococcal groups found in the oral cavity—is found in high quantities in the plaque biofilm associated with carious lesions, and is also more aciduric than other oral bacteria in the Streptococcus species.^6–8 S. mutans tolerates a highly acidic environment, allowing it to further the progression of caries. S. sobrinus uses glucose for acid production more rapidly than S. mutans and is more cariogenic than S. mutans.^9,10 Lactobacilli depend on S. mutans to colonize in the oral cavity through the creation of a “retentive niche.”¹¹ A low pH environment and exposure to fermentable carbohydrates are then all that is needed for lactobacilli to colonize and further the progression of carious lesions.

THE USE OF MOUTHRINSES

Different ingredients in mouthrinses can reduce cariogenic bacteria. In a study on the antimicrobial efficacy of mouthrinses containing chlorhexidine, sodium fluoride, fluoride with essential oils, alum, green tea, and garlic with lime, results showed that chlorhexidine was the most effective against S. mutans and lactobacilli, followed by the garlic with lime mouthrinse.¹² ­However, the garlic with lime mouthrinse needs more scientific evaluation. The study also showed that green tea and alum mouthrinses were less effective in reducing cariogenic bacteria than the other mouthrinses tested but still showed inhibitory effects on S. mutans and lactobacilli.¹²

The effect of mouthrinses containing essential oils, chlorhexidine, benzethonium chloride, and povidone-iodine on cariogenic bacteria were studied by Oyanagi et al.¹³ Results showed that the rinses containing essential oils and chlorhexidine were highly successful in eliminating significant numbers of planktonic bacteria and bacteria enmeshed within biofilms. The essential oil mouthrinse also demonstrated inhibitory capabilities that helped to prevent demineralization.

Tehrani et al¹⁴ conducted a study comparing sodium fluoride mouthrinses with green tea mouthrinses. Results showed that both mouthrinses were effective in reducing the colony counts of S. mutans and lactobacilli. The difference between the two mouthrinses was in their mechanisms of action. Sodium fluoride prevents S. mutans from adhering to the tooth structure, inhibits demineralization, and remineralizes incipient carious lesions.¹⁵ Green tea polyphenols inhibit the growth of S. mutans, S. sobrinus, and lactobacilli, and prevent S. mutans from attaching to the tooth structure.^16–18 Green tea mouthrinses may be a good option in reducing cariogenic bacteria, but they do not remineralize incipient carious lesions, as sodium fluoride does.¹⁵ Sodium fluoride mouthrinses are contraindicated in children younger than age 6 age due to the risk of ingestion.¹⁹

In a study comparing povidone-iodine and chlorhexidine mouth­rinses, children at high-caries risk were divided into three groups following restorative treatment: the first group received the 1% povidone-iodine mouthrinse, the second group received the 0.2% chlorhexidine mouthrinse, and the third group received the placebo mouthrinse.²⁰ All groups showed significant reductions in S. mutans immediately after mouthrinse therapy, with higher reductions seen among the first group. Unfortunately, after 15 days, 30 days, and 90 days, S. mutans counts in all three groups increased, demonstrating a short duration of efficacy.

Additional studies found that the inclusion of povidone-iodine in mouthrinses significantly reduced S. mutans when applied in 3-month intervals over 1 year.^21,22 Using the mouthrinses for short periods and introducing them again in a few months may keep the bacterial count down over a longer duration. To reduce the bacterial count even further, 7.5% povidone-iodine mouthrinses can be used, followed by 0.2% chlorhexidine mouthrinses.²³ Contraindications to povidone-iodine mouthrinses include sensitivities to iodine and any pre-existing thyroid disorders.²⁴

A study conducted on children with high-caries risk showed a significant reduction in S. mutans using both chlorhexidine mouthrinses and sodium fluoride mouthrinses.²⁵ Chlorhexidine is known as the gold standard in reducing cariogenic bacteria, while sodium fluoride is considered the gold standard of caries prevention.^12,14,26 However, patient compliance with chlorhexidine mouthrinses may be low due to the taste, staining of teeth, and risk of taste alteration.^26–29

A review of the literature regarding the effects of cetylpyridinium chloride (CPC) showed that CPC is effective in plaque control, reducing gingivitis, and reducing gingival bleeding.^31–34 An article comparing mouthrinses with CPC and sodium fluoride revealed that CPC-containing test rinses with and without fluoride were both highly bactericidal against S. mutans.³⁵ The results showed that fluoride did not reduce the antibacterial efficacy of CPC, nor did CPC reduce the efficacy of fluoride in inhibiting demineralization.³⁵

Mouthrinses containing chlorine dioxide may also decrease plaque scores. In a study conducted on mouthrinses containing aloe vera, chlorine dioxide, and chlorhexidine, both the chlorhexidine and chlorine dioxide rinses caused significant reduction of plaque scores. The study authors suggest that chlorine dioxide may be a suitable alternative for chlorhexidine but more research is indicated.³⁶

Xylitol also provides plaque-reducing qualities. In a study that investigated mouthrinses containing chlorhexidine, xylitol, and a combination of chlorhexidine and xylitol against S. sanguis and S. mutans, results showed the combination of xylitol and chlorhexidine was most effective against the cariogenic species.³⁷

CONCLUSION

The use of mouthrinses is an important adjunct to mechanical removal of plaque, as some ingredients have been found to reduce the prevalence of S. mutans. Dental hygienists should stay up to date on the benefits of different ingredients in mouthrinses in order to educate their patients on the most effective mouthrinses to reduce the cariogenic load in their patients’ oral cavities. Incorporating mouthrinse recommendations and directions into oral hygiene instructions can improve patient health, along with the appropriate toothbrushing and interproximal cleaning technique. Evaluating the effectiveness of certain ingredients on the reduction of cariogenic bacteria will aid in the creation of mouthrinses that can reduce these bacteria with fewer side effects.

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From Dimensions of Dental Hygiene. November 2019;17(10):18—20.