Quantitative analysis of the effects of essential oil mouthrinses on clinical plaque microbiome: a parallel-group, randomized trial

BACKGROUND

The rich diversity of microorganisms in the oral cavity plays an important role in the maintenance of oral health and development of detrimental oral health conditions. Beyond commonly used qualitative microbiome metrics, such as relative proportions or diversity, both the species-level identification and quantification of bacteria are key to understanding clinical disease associations. This study reports the first-time application of an absolute quantitative microbiome analysis using spiked DNA standards and shotgun metagenome sequencing to assess the efficacy and safety of product intervention on dental plaque microbiome.

METHODS

In this parallel-group, randomized clinical trial, essential oil mouthrinses, including LISTERINE® Cool Mint Antiseptic (LCM), an alcohol-containing prototype mouthrinse (ACPM), and an alcohol-free prototype mouthrinse (AFPM), were compared against a hydroalcohol control rinse on clinical parameters and the oral microbiome of subjects with moderate gingivitis. To enable a sensitive and clinically meaningful measure of bacterial abundances, species were categorized according to their associations with oral conditions based on published literature and quantified using known amounts of spiked DNA standards.

RESULTS

Multivariate analysis showed that both LCM and ACPM shifted the dysbiotic microbiome composition of subjects with gingivitis to a healthier state after 4 weeks of twice-daily use, resembling the composition of subjects with clinically healthy oral conditions recruited for observational reference comparison at baseline. The essential oil-containing mouthrinses evaluated in this study showed statistically significant reductions in clinical gingivitis and plaque measurements when compared to the hydroalcohol control rinse after 6 weeks of use.

CONCLUSIONS

By establishing a novel quantitative method for microbiome analysis, this study sheds light on the mechanisms of LCM mouthrinse efficacy on oral microbial ecology, demonstrating that repeated usage non-selectively resets a gingivitis-like oral microbiome toward that of a healthy oral cavity.

TRIAL REGISTRATION

The trial was registered on ClinicalTrials.gov on 10/06/2021. The registration number is NCT04921371.

Soft, adhesive (+) alpha tocopherol phosphate planar bilayers that control oral biofilm growth through a substantive antimicrobial effect

'Soft' nanomaterials have the potential to produce substantive antibiofilm effects. The aim of this study was to understand the oral antimicrobial activity of soft nanomaterials generated from alpha-tocopherol (α-T) and alpha-tocopherol phosphate (α-TP). (+) α-TP formed planar bilayer islands (175 ± 21 nm, -14.9 ± 3.5 mV) in a Trizma® buffer, whereas (+) α-T formed spherical liposomes (563 ± 1 nm, -10.5 ± 0.2 mV). The (+) α-TP bilayers displayed superior Streptococcus oralis biofilm growth retardation, a more substantive action, generated a superior adsorption to hydroxyapatite and showed an enhanced inhibition of multi-species bacterial saliva biofilm growth (38 ± 7μm vs 58 ± 18 μm, P ˂ 0.05) compared to (+) α-T. Atomic force microscopy data indicated that the ability of the 'soft' α-TP nanomaterials to transition into planar bilayer structures upon contact with interfaces facilitated their adhesive properties and substantive antimicrobial effects.

In vitro efficacy of essential oil mouthrinse versus dentifrices

OBJECTIVES

To compare the antimicrobial efficacy and kill penetration of essential oils (EO) mouthrinse versus stannous fluoride, and triclosan dentifrice slurries on saliva-derived biofilms using confocal laser scanning microscopy (CLSM).

METHODS

Saliva-derived biofilms were grown for 48h on hydroxyapatite discs using pooled, homogenized saliva from 8 healthy volunteers as the inoculum. The mean thickness of these biofilms was 84μm (range, 23-241μm). CLSM with viability mapping was used to visualize the antimicrobial kill penetration of each treatment regime within a biofilm.

RESULTS

At 30s treatment durations, CLSM imaging revealed greater antimicrobial activity and kill penetration of EO mouthrinse compared to sodium fluoride-, stannous fluoride-, and triclosan-containing dentifrice slurries. Quantification of biovolume revealed that EO mouthrinse treatment at 30s resulted in a greater non-viable biovolume proportion (84.6%±15.0%) than other treatment groups. Increasing the treatment duration of the triclosan dentifrice (to 60 and 120s) resulted in better penetration and an increased reduction of viable cells, comparable to EO mouthrinse treatment at 30s duration. Further, CLSM imaging showed that the combined treatment of a non-antimicrobial dentifrice (45s) with EO mouthrinse (30s) showed superior antimicrobial activity (96.2%±3.7%) compared to the antimicrobial triclosan-containing dentifrice used without a mouthrinse step (26.0%±32.0%).

CONCLUSIONS

Within typical exposure times, the EO-containing mouthrinse can penetrate deep into the accumulating plaque biofilm compared to the chemotherapeutic dentifrice slurries, and may provide an efficacious alternative to triclosan, when used as an adjunct with a mechanical oral care regimen.

CLINICAL SIGNIFICANCE

Using viability mapping and CLSM, this study demonstrated that EO-containing mouthrinse penetrates and kills microorganisms deeper and more effectively in plaque biofilm in typical exposure times when compared to dentifrice chemotherapeutic agents, providing an efficacious alternative to triclosan or stannous fluoride when used as an adjunct to mechanical oral care.

Biomimetic ultrathin whitening by capillary-force-induced random clustering of hydrogel micropillar arrays

Capillary-force-induced collapse of high-aspect-ratio microstructures has often been considered a failure mechanism in device fabrication. Here, we study capillary-force-induced clustering behavior of highly ordered hydrogel micropillar arrays from 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) and explore their utility as ultrathin whitening layers (less than 9 mum thick). When exposed to water, followed by drying in an air stream, the micropillars were softened, bent, and randomly clustered together because of competition between the capillary force and elastic restoring force of the pillars. By varying the relative composition of the water-swellable PHEMA and glassy PMMA, we modulated the elastic modulus of the pillars in the wet state spanning over 3 orders of magnitude. By minimizing the sum of the capillary meniscus interaction energy and the elastic bending energy of the pillars for a cluster, we estimated the average cluster size as a function of the elastic modulus of the pillars, which agreed well with the experimental observation. The randomly clustered micropillar arrays appeared white in color because of random light scattering from the clusters, similar to the observation in the white beetles, whose scales consist of a few micrometer-thick random networks of microfilaments.

Relationship between dentifrice fluoride concentration and clinical caries reduction

PURPOSE

To review the published literature on clinical caries trials of fluoride dentifrices and to combine their results in order to evaluate the correlation between fluoride concentration in dentifrice formulations and their anticaries efficacy, i.e., the dose-response relationship.

METHODS

All available dentifrice caries clinical trials reported in the literature of products having at least two fluoride concentrations greater than 0 ppm were reviewed, graphed and statistically analyzed.

RESULTS

The evaluation supported a linear correlation between the fluoride concentration of dentifrices between 0 and 5000 ppm F and clinical caries efficacy.

Anticaries efficacy of a new dentifrice for hypersensitivity

PURPOSE

To evaluate the expected anticaries efficacy of a new dentifrice containing stannous fluoride as the anticaries agent and potassium nitrate as the antihypersensitivity agent using a series of laboratory and animal studies.

METHODS

Four surrogate studies were performed in this assessment including fluoride uptake in sound enamel, enamel solubility reduction, fluoride bioavailability and animal caries.

RESULTS

Each of these studies indicated the new dentifrice for hypersensitivity (Colgate Sensitive Maximum Strength) was effective in inhibiting the caries process. The data demonstrate that this new dentifrice is predicted to be highly effective against caries and equivalent to a positive control dentifrice.

The scientific rationale and development of an optimized stannous fluoride dentifrice, Part 1

Stannous fluoride has been recognized as an effective anticavity therapeutic agent since the early 1950s. There has recently been a resurgence in activity to discover ways to fully exploit its documented antimicrobial activity. Through the use of targeted in vitro methodology to predict in vivo efficacy, a highly optimized stannous fluoride dentifrice has been developed. Careful selection of stabilizing agents formulated into a unique system has resulted in a Colgate Optimized Stannous Fluoride (COSF) dentifrice that has been proven to simultaneously help control supragingival plaque, gingivitis, supragingival calculus, and caries. Furthermore, the COSF dentifrice has been clinically shown not to cause the traditional stannous fluoride staining of dentition.

The effects of outward forced convective flow on inward diffusion of potassium across human dentin

PURPOSE

To measure the inward flux of potassium across human dentin disks, in vitro, in the absence and then in the presence of a simulated pulpal pressure (PP), before and after brushing with two desensitizing dentifrices.

MATERIALS AND METHODS

Dentin discs were made from extracted unerupted third molars and etched with 6% citric acid to remove the smear layers. The hydraulic conductance (Lp or outward fluid movement) of the discs was measured before and after brushing for 2 minutes with two desensitizing dentifrices, Colgate Sensitive Maximum Strength or Sensodyne Fresh Mint, both dentifrices containing 5% potassium nitrate. The potassium flux was measured at a pressure of 0 cm H2O, and a simulated pulpal pressure of 20 cm H2O.

RESULTS

The results showed the Colgate-brushed specimens had lower Lp (P < 0.05) than specimens brushed with Sensodyne or with saline. The Colgate-brushed specimens had a corresponding lower K+ flux, at a PP = 0 cm H2O, than specimens brushed with saline, but were not significantly different than specimens brushed with Sensodyne dentifrice. However, when the pressure was increased from 0 to 20 cm H2O, to simulate outward dentin fluid pressure, there were significant decreases in K+ flux across all three treatment groups, but the K+ flux of the Colgate-brushed specimens were affected the least, resulting in the Colgate-brushed specimens having significantly (P < 0.05) greater K+ fluxes than the saline or Sensodyne dentifrice-brushed groups. The magnitude of reduction in K+ flux in going from 0 cm H2O to 20 cm H2O was demonstrated to be linearly related to the magnitude of the Lp of the brushed specimens. Hence, a small Lp corresponded to a small reduction in K+ flux, and a correspondingly large K+ flux at 20 cm H2O. An explanation of this phenomenon is that a decrease in the Lp of dentin, produced by brushing, corresponds to a decreased outward dentin fluid flow. This lowers the outward K+ convective flow and also lowers the inward K+ diffusion. However, since the decrease of the outward K+ convective flow is greater than the decrease of the inward K+ diffusion, and the net flux is the algebraic sum of these two terms, the result is greater net inward K+ flux through the dentin. Therefore, the Colgate-brushed specimens, which exhibited the lowest Lp, provided the greatest inward K+ flux at simulated dentin fluid pressure.