How Essential Oil Rinses Create a Healthier Mouth

How Essential Oil Rinses Create a Healthier Mouth | Image Credit: © Romaset - stock.adobe.com

During more than a century spent studying Listerine®, Kenvue, Inc has established plenty of evidence that the solution improves oral health. But exactly how does this family of rinses accomplish that?

Antimicrobial rinses work by helping to create a healthier balance within the oral microbiome, with Listerine relying on 4 essential oils — eucalyptol, menthol, methyl salicylate and thymol — to kill 99.9% of germs that cause bad breath, plaque and gingivitis. But just how these ingredients drive those changes is still a bit of a mystery, as scientific exploration into this complex area of human health is only starting to emerge.

At Kenvue, our research and development teams have begun looking more closely at this dynamic, and we’re excited to learn more about why these products make a difference in oral health and how we can increase their effectiveness. Listerine is a brand of Johnson & Johnson Consumer Inc., a subsidiary of Kenvue.

In our first foray into this area, we conducted studies that were published recently in 3 BMC Oral Health articles. In addition to reaffirming that essential oil mouthwashes add to the effectiveness of brushing and flossing, we shed light on how the rinses induce those improvements by creating a smaller, better-balanced population of bacteria in the mouth.¹

In the first study, we tested a novel method that made it possible to identify bacterial species, and assessed the changes in the numbers of the different types of bacteria during treatment. Researchers used spike DNA standards, meaning that they added artificial DNA into biologic samples as reference points, and then applied shotgun metagenomic sequencing. This enabled them to sample the genetic content of every species they found and measure bacterial numbers down to the individual cell level.

In a second study, Kenvue experts evaluated the clinical outcomes of a brushing, flossing, and rinsing routine. And in a sub-analysis using the new measurement technique, they quantified the bacteria collected in that study and examined their types and quantities in relation to clinically meaningful oral health outcomes.

The results, verified through the sub-analysis, were compelling. We learned that a regimen of brushing, flossing and rinsing is 5 times more effective at reducing supragingival plaque and gingivitis than brushing and flossing alone, and that the addition of an antimicrobial mouthrinse also reduces plaque bacteria below the gumline.² And we found that newer, milder-tasting rinses such as Listerine Cool Mint Zero Alcohol support the same kinds of benefits as our original robustly flavored formulas.

Although the subjects population was fairly homogenous, we believe these studies provide a promising start to our industry’s early understanding of how over-the-counter rinses affect oral health — particularly when it comes to the susceptibility of specific types of bacteria to these products. As we prepare to take a deeper dive into this area of research, we’re looking forward to inviting a range of medical and industry leaders to engage with us for guidance.

Ultimately, we hope our findings will do more than provide new evidence for the use of essential oil rinses. By helping scientists to better understand oral disease progression, we anticipate that this research will lead to new innovations in the control of plaque and gingivitis.

Testing A Novel Measurement System

The first randomized, controlled study ³ in the series, conducted between October and December of 2019, bypassed conventional qualitative microbiome measurements such as relative proportions, instead applying our novel method of analysis.

We reported results for 121 people with moderate gingivitis, along with 32 healthy volunteers. In addition to brushing twice daily, they were randomly assigned to use one of 4 rinses twice a day for 6 weeks: Listerine Cool Mint Antiseptic, a commercially available alcohol-based essential oil rinse; a prototype flavored essential oil rinse containing alcohol; a prototype flavored essential oil rinse that was free of alcohol; and a hydroalcohol control (placebo mouthwash).

Supragingival plaque was collected 4 times throughout the study for microbiome analysis from all 4 treatment groups. Microbiome results for each experimental group were compared with the placebo mouthwash, and with those healthy volunteers whose microbiome samples were collected only at baseline.

All treatments were well tolerated.

There were significant improvements in clinical signs of gingivitis, plaque and bleeding in each of the 3 treatment groups. Compared to the control, all the rinses reduced gingivitis by at least 37.4% and bleeding by at least 36.3%.

Listerine Cool Mint Antiseptic also significantly reduced plaque by at least 22% after 4 weeks, with further improvements seen at 6 weeks; meanwhile, the alcohol-free rinse logged a significant plaque reduction of 14% after 6 weeks.

So, what does this say about the microbiome?

By using a literature search to sort bacterial species into categories associated with good or bad oral health, the researchers found 213 oral species at the study population level, and then examined their responses to treatment. Overall, patients with gingivitis had elevated amounts of total bacteria including species that are associated with gingivitis compared to the healthy reference subjects. Furthermore, bacterial load, richness and diversity were reduced after dental prophylaxis and the first rinse. This result showed a substantial impact, but it is important to note that neither of these interventions eradicated all of the bacteria. For participants using Listerine Cool Mint that shift persisted throughout the study.

Assessing Clinical Outcomes

Our second randomized study⁴, conducted from April through July 2022, followed up on previous findings⁵ that an alcohol-based essential oil rinse, when added to a routine of brushing with or without flossing, significantly reduced supragingival plaque, gingivitis and bleeding after 12 weeks.

Our goal was to consider the relative efficacy of an alcohol-free essential oil rinse in that setting.

The study included 254 adult subjects who completed the study (a total of 270 subjects were randomized) with gingivitis and 30 healthy volunteers who served as a microbiome comparator group. After a cleaning that removed all calculus and plaque, participants were randomly assigned in equal numbers to:

1. Brush with fluoridated toothpaste twice daily (the control group);
2. Brush twice-daily and use Listerine Cool Mint Antiseptic, an alcohol-based essential oil rinse, twice-daily;
3. Brush twice-daily and use Listerine Cool Mint Zero Alcohol, an alcohol-free essential oil rinse, twice-daily;
4. Brush twice-daily and floss once-daily;
5. Brush twice-daily, floss once-daily and use the alcohol-free rinse twice-daily.

Compared with those who strictly brushed, all participants using rinse experienced statistically significant reductions in gingivitis and supragingival plaque after 12 weeks.

At week 12, compared with the brushing-only group, we recorded a statistically significant mean reduction in interproximal plaque in the rinse cohorts: 30.8% in the group that used alcohol-based rinse and 18.2% in the group that used alcohol-free rinse. At the same time point, the alcohol-based and alcohol-free rinses were associated with reduced interproximal gingivitis by a statistically significant 39% and 36.9%, respectively. The rinses also reduced plaque, gingivitis and bleeding in between the teeth.

Fifteen participants experienced mild or moderate adverse events, including oral mucosal exfoliation — all of which resolved without treatment.

Exploring Results Through a Sub-Analysis

A sub-analysis of that study evaluated the microbiome of supragingival plaque at baseline and at 4 and 12 weeks, also assessing viable bacteria in subgingival plaque at 12 weeks via live/dead polymerase chain reaction (PCR).

Through metagenomic sequencing and a literature review, researchers found 120 species per individual patient level, encompassing 236 taxa, that were native to the oral cavity — 91 commensal and others associated with gingivitis, malodor or acidogenesis.

Only groups that paired brushing with rinsing experienced significant reductions in bacterial diversity, richness and abundance, in either alcohol or alcohol-free rinse. At 12 weeks, the alcohol-based versus alcohol-free rinses reduced the quantity of gingivitis bacteria by 91.3% versus 80.2% and quantity of malodor bacteria by 85.2% versus 68.5%, respectively.

Compared with brushing alone, all the rinse groups also demonstrated significant reductions in plaque markers. Furthermore, PCR determined that adding flossing and rinsing to brushing significantly reduced bacterial abundance in subgingival plaque, particularly F. nucleatum and P. gingivalis.

Finally, the study found that flossing and rinsing reduced total bacteria in plaque below the gumline, helping to explain our clinical findings of reduced gingivitis and bleeding in this study population.

Strengthening Research and Development

Despite decades of studies confirming the safety and efficacy of our essential oil rinses, there is education needed on the different types of rinses available to patients. There are various types of mouthrinses including over the counter and prescription options. Listerine rinses reduce bacterial load with 4 essential oils, while promoting the growth of good bacteria, which repopulate faster than bad bacteria. Listerine has a long history, and having extensively studied our wide range of essential oil rinses, we have established they not only deliver oral health outcomes but are safe and effective when used as directed on their labels, twice daily.

Our recent studies go a step further by confirming the safety and efficacy of Listerine rinses in a brushing and flossing routine.

That’s key, as the American Dental Association has long recommended brushing and flossing for at-home oral care, and it’s crucial for dentists to understand the health benefits of adding an antimicrobial rinse.

Beyond that, dental professionals should watch for further scientific developments as research scientists, leaders in dentistry and other stakeholders work together to understand the oral microbiome and determine the direction of future research. Kenvue is excited to help move the needle in this emerging area of scientific exploration, and we look forward to contributing to a new wave of innovation in the fight against plaque and gingivitis.

If you would like to engage with Kenvue about our studies or contribute to future research, please contact Jessica Snell at Kenvue.

References:

1. Min, K., Glowacki, A.J., Bosma, M.L. et al. Quantitative analysis of the effects of essential oil mouthrinses on clinical plaque microbiome: a parallel-group, randomized trial. BMC Oral Health 24, 578 (2024). https://doi.org/10.1186/s12903-024-04365-92.

2. Min, K., Bosma, M.L., John, G. et al. Quantitative analysis of the effects of brushing, flossing, and mouthrinsing on supragingival and subgingival plaque microbiota: 12-week clinical trial. BMC Oral Health 24, 575 (2024). https://doi.org/10.1186/s12903-024-04362-y3.

3. Quantitative analysis of the effects of essential oil mouthrinses on clinical plaque microbiome: a parallel-group, randomized trial | BMC Oral Health | Full Text (biomedcentral.com)

4. Quantitative analysis of the effects of brushing, flossing, and mouthrinsing on supragingival and subgingival plaque microbiota: 12-week clinical trial | BMC Oral Health (springer.com)

5. Comparative Effectiveness of Toothbrushing, Flossing and Mouthrinse Regimens on Plaque and Gingivitis: A 12-week virtually supervised clinical trial | Journal of Dental Hygiene (adha.org)