Understanding the Role of Shape and Composition of Star-Shaped Polymers and their Ability to Both Bind and Prevent Bacteria Attachment on Oral Relevant Surfaces.

In this study, we have prepared a series of 4- and 6-arm star-shaped polymers with varying molecular weight and hydrophobicity in order to provide insight into the role and relationship that shape and composition have on the binding and protecting of oral relevant surfaces (hydroxyapatite, HAP) from bacteria colonization. Star-shaped acrylic acid polymers were prepared by free-radical polymerization in the presence of chain transfer agents with thiol groups, and their binding to the HAP surfaces and subsequent bacteria repulsion was measured. We observed that binding was dependent on both polymer shape and hydrophobicity (star vs. linear), but their relative efficacy to reduce oral bacteria attachment from surfaces was dependent on their hydrophobicity only. We further measured the macroscopic effects of these materials to modify the mucin-coated HAP surfaces through contact angle experiments; the degree of angle change was dependent on the relative hydrophobicity of the materials suggesting future in vivo efficacy. The results from this study highlight that star-shaped polymers represent a new material platform for the development of dental applications to control bacterial adhesion which can lead to tooth decay, with various compositional and structural aspects of materials being vital to effectively design oral care products.

Reduction of bacterial attachment on hydroxyapatite surfaces: Using hydrophobicity and chemical functionality to enhance surface retention and prevent attachment.

Water-soluble, linear polymers with high-acid functionality are commonly used in oral care formulations to provide benefits such as bioactive complexation and delivery, as well as inhibition of the bacteria deposition and colonization, commonly referred to as 'anti-attachment'. Unfortunately, structure-activity relationship (SAR) studies of these polymers are scarce, thus, a systematic approach to design polymers with a desired property (e.g. anti-attachment) is limited. Multifunctional anti-attachment amphiphilic molecules (AMs) featuring a sugar backbone, hydrophobic arms, a poly(ethylene glycol) tail, and a chemical anchor effectively deposited on soft ceramic surfaces and reduced bacterial adhesion. The chemical compositions of the AMs were fine-tuned to better coordinate with dental enamel surfaces and prevent bacterial colonization. A graft-to approach was used to investigate the effect of the chemical anchor on AM deposition and retention. The chemical composition, absorption/desorption, and wettability properties of the bioactives and bioactive-coated surfaces were investigated using nuclear magnetic resonance, X-ray photon spectroscopy, quartz crystal microbalance, and contact angle. In addition, the ability of the AMs to provide anti-bacterial attachment on a simulated enamel surface was evaluated in vitro using bacterial repulsion assays. The SAR between surface retention and anti-attachment properties of the AMs demonstrates the feasibility and tunability of using these polymers as bioactive agents that provide anti-attachment benefits on dental enamel surfaces.

In vitro Increased Respiratory Activity of Selected Oral Bacteria May Explain Competitive and Collaborative Interactions in the Oral Microbiome.

Understanding the driving forces behind the shifts in the ecological balance of the oral microbiota will become essential for the future management and treatment of periodontitis. As the use of competitive approaches for modulating bacterial outgrowth is unexplored in the oral ecosystem, our study aimed to investigate both the associations among groups of functional compounds and the impact of individual substrates on selected members of the oral microbiome. We employed the Phenotype Microarray high-throughput technology to analyse the microbial cellular phenotypes of 15 oral bacteria. Multivariate statistical analysis was used to detect respiratory activity triggers and to assess similar metabolic activities. Carbon and nitrogen were relevant for the respiration of health-associated bacteria, explaining competitive interactions when grown in biofilms. Carbon, nitrogen, and peptides tended to decrease the respiratory activity of all pathobionts, but not significantly. None of the evaluated compounds significantly increased activity of pathobionts at both 24 and 48 h. Additionally, metabolite requirements of pathobionts were dissimilar, suggesting that collective modulation of their respiratory activity may be challenging. Flow cytometry indicated that the metabolic activity detected in the Biolog plates may not be a direct result of the number of bacterial cells. In addition, damage to the cell membrane may not influence overall respiratory activity. Our methodology confirmed previously reported competitive and collaborative interactions among bacterial groups, which could be used either as marker of health status or as targets for modulation of the oral environment.

Competitive Adsorption of Polyelectrolytes onto and into Pellicle-Coated Hydroxyapatite Investigated by QCM-D and Force Spectroscopy.

A current effort in preventive dentistry is to inhibit surface attachment of bacteria using antibacterial polymer coatings on the tooth surface. For the antibacterial coatings, the physisorption of anionic and cationic polymers directly onto hydroxyapatite (HA) and saliva-treated HA surfaces was studied using quartz crystal microbalance, force spectroscopy, and atomic force microscopy. First, single species adsorption is shown to be stronger on HA surfaces than on silicon oxide surfaces for all polymers (i.e., Gantrez, sodium hyaluronate (NaHa), and poly(allylamine-co-allylguanidinium) (PAA-G75)). It is observed through pH dependence of Gantrez, NaHa, and PAA-G75 adsorption on HA surfaces that anionic polymers swell at high pH and collapse at low pH, whereas cationic polymers behave in the opposite fashion. Thicknesses of Gantrez, NaHa, and PAA-G75 are 52 nm (46 nm), 35 nm (11 nm), and 6 nm (54 nm) at pH 7 (3.5), respectively. Second, absorption of charged polymer is followed by absorption of the oppositely charged polymer. Upon exposure of the anionic polymer layers, Gantrez and NaHa, to the cationic polymer, PAA-G75, films collapse from 52 to 8 nm and 35 to 11 nm, respectively. This decrease in film thickness is attributed to the electrostatic cross-linking between anionic and cationic polymers. Third, for HA surfaces pretreated with artificial saliva (AS), the total thickness decreases from 25 to 16 nm upon exposure to PAA-G75. Force spectroscopy is used to further investigate the PAA-G75/AS coating. The results show that the interaction between a negatively charged colloidal bead and the AS surface is strongly repulsive, whereas PAA-G75/AS is attractive but varies across the surface. Additionally, AFM studies show that AS/HA is smooth with a RMS roughness of 1.7 nm, and PAA-G75-treated AS/HA is rough (RMS roughness of 5.4 nm) with patches of polymer distributed across the surface with an underlying coating. The high roughness of PAA-G75 treated AS/HA is attributed to the strong adsorption of the relatively small PAA-G75 onto the heterogeneously distributed negatively charged AS surface. In addition, uptake of PAA-G75 by pellicle layer (saliva-treated HA surface) is observed, and the adsorbed amount of PAA-G75 on/into pellicle layer is ∼2 times more than that on/into AS layer. These studies show that polymer adsorption onto HA and saliva-coated HA depends strongly on the polymer type and size and that there is an electrostatic interaction between polymer and saliva and/or oppositely charged polymers that stabilizes the coatings on HA. Lastly, assessing the viability of the adherent bacteria collected from the PAA-G75-coated surfaces showed a significant reduction (∼93%) in bacterial viability when compared to bacteria collected from untreated and Gantrez-coated HA. These results suggest the potential antimicrobial activity of PAA-G75.

Nutritional stimulation of commensal oral bacteria suppresses pathogens: the prebiotic concept.

AIM: To identify potential oral prebiotics that selectively stimulate commensal, albeit beneficial bacteria of the resident oral microbial community while suppressing the growth of pathogenic bacteria. MATERIAL AND METHODS: Using Phenotype MicroArrays as a high-throughput method, the change in respiratory activity of 16 oral bacteria in response to 742 nutritional compounds was screened. Most promising prebiotic compounds were selected and applied in single species growth and biofilm formation assays, as well as dual species (beneficial-pathogen) competition assays. RESULTS: Increased respiratory activity could not always be related to an increase in growth or biofilm formation. Six compounds were used in dual species competition assays to directly monitor if selective nutritional stimulation of the beneficial bacterium results in the suppression of the pathogenic bacterium. Two compounds, beta-methyl-d-galactoside and N-acetyl-d-mannosamine, could be identified as potential oral prebiotic compounds, triggering selectively beneficial oral bacteria throughout the experiments and shifting dual species biofilm communities towards a beneficial dominating composition at in vitro level. CONCLUSION: Our observations support the hypothesis that nutritional stimulation of beneficial bacteria by prebiotics could be used to restore the microbial balance in the oral cavity and by this promote oral health.

Bioinspired amphiphilic phosphate block copolymers as non-fluoride materials to prevent dental erosion.

Inspired by the fact that certain natural proteins, e.g. casein phosphopeptide or amelogenin, are able to prevent tooth erosion (mineral loss) and to enhance tooth remineralization, a synthetic amphiphilic diblock copolymer, containing a hydrophilic methacryloyloxyethyl phosphate block (MOEP) and a hydrophobic methyl methacrylate block (MMA), was designed as a novel non-fluoride agent to prevent tooth erosion under acidic conditions. The structure of the polymer, synthesized by reversible addition-fragment transfer (RAFT) polymerization, was confirmed by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (NMR). While the hydrophilic PMOEP block within the amphiphilic block copolymer strongly binds to the enamel surface, the PMMA block forms a hydrophobic shell to prevent acid attack on tooth enamel, thus preventing/reducing acid erosion. The polymer treatment not only effectively decreased the mineral loss of hydroxyapatite (HAP) by 36-46% compared to the untreated control, but also protected the surface morphology of the enamel specimen following exposure to acid. Additionally, experimental results confirmed that low pH values and high polymer concentrations facilitate polymer binding. Thus, the preliminary data suggests that this new amphiphilic diblock copolymer has the potential to be used as a non-fluoride ingredient for mouth-rinse or toothpaste to prevent/reduce tooth erosion.

Anti-hypersensitivity mechanism of action for a dentifrice containing 0.3% triclosan, 2.0% PVM/MA copolymer, 0.243% NaF and specially-designed silica.

PURPOSE: To evaluate the laboratory dentin occlusion efficacy and effects on dentin permeability of a new multi-benefit dentifrice in order to gain insight into the mechanism of action of a novel technology for dentin hypersensitivity relief based on a specially-designed silica and copolymer system. METHODS: Acid-etched human dentin was evaluated with confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) after treatment with one of the following: (1) a dentifrice containing 0.3% triclosan, 2.0% PVM/MA copolymer, 0.243% sodium fluoride with specially designed silica (Test Dentifrice 1); (2) a dentifrice containing 0.3% triclosan and the same overall silica loading as Test Dentifrice 1 but without copolymer and the specially-designed silica (Placebo Dentifrice); (3) a commercially-available dentifrice containing 0.454% stannous fluoride in a silica base with sodium hexametaphosphate and zinc lactate (Test Dentifrice 2); and (4) a commercially-available non-sensitive dentifrice containing 0.243% sodium fluoride in a silica base (Negative Control Dentifrice). The composition of dentin treated with either Test Dentifrice 1 or Negative Control Dentifrice was analyzed using energy dispersive x-ray (EDX) and electron spectroscopy for chemical analysis (ESCA). To highlight dentin occluding efficacy of the specially-designed silica, dentin was treated with Test Dentifrice 1 formulated with fluorescently-tagged specially-designed silica and resulting occlusion followed with CLSM. The dentin occluding abilities of Test Dentifrices 1 and 2 were compared with the Negative Control dentifrice using CLSM after a 4-day cycling model consisting of twice daily dentifrice treatment and four acid challenges. Effects of treatment with Test Dentifrices 1 or 2 on dentin permeability and subsequent resistance of occluding deposits to acid dissolution and dislodgement by pulpal pressure were assessed using hydraulic conductance. RESULTS: Dentin specimens treated with Test Dentifrices 1 and 2 were significantly occluded compared to Placebo Dentifrice and Negative Control Dentifrice when visualized with CLSM. The level of occlusion remaining after challenge with cola was highest for dentin treated with Test Dentifrice 1 in CLSM xz views. Test Dentifrice 1 produced dentin surface deposits and tubule plugs containing silicon in addition to calcium and phosphorus as indicated by ESCA and EDX. CLSM visualization of fluorescently-tagged material confirmed occlusion by the specially-designed silica which was localized at the dentin tubule openings. Imaging of dentin by CLSM after the 4-day cycling model revealed a significantly higher amount of occluded tubules for dentin treated with Test Dentifrice 1 compared to the Negative Control Dentifrice or Test Dentifrice 2. Etched dentin treated with the Test Dentifrice 1 was significantly less permeable compared to that treated with the Negative Control Dentifrice, exhibiting over 80% reduction in dentin permeability. The occlusion provided by the Test Dentifrice 1 was maintained and provided significantly better reduction in permeability after extended pulpal pressure and acid challenge compared to dentin treated with Test Dentifrice 2.

A breakthrough therapy for dentin hypersensitivity: how dental products containing 8% arginine and calcium carbonate work to deliver effective relief of sensitive teeth.

OBJECTIVE: These studies have utilized a range of state-of-the-art surface techniques to gain insight into the mechanism of action of a new technology for dentin hypersensitivity relief based upon arginine and calcium carbonate and, in particular, to address important questions regarding the nature and extent of dentin tubule occlusion. METHODS: Confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) have been used to assess tubule occlusion. Energy dispersive x-ray (EDX) and electron spectroscopy for chemical analysis (ESCA) have been used to identify the composition of the dentin plug. CLSM has also been used to compare the mechanism of action of the toothpaste and the desensitizing prophylaxis paste, to address whether both the arginine and the calcium carbonate components are essential to occlusion, to identify the location of the arginine within the occluded dentin, and to demonstrate resistance of the occlusion to acid challenge. Hydraulic conductance has been used to assess the effectiveness of the arginine-calcium carbonate technology in arresting dentin fluid movement, to evaluate the effects of pulpal pressure on the robustness of the occlusion, and to confirm the resistance of the occlusion to an acid challenge. RESULTS: The CLSM, SEM, and AFM studies demonstrate that the arginine-calcium carbonate technology is highly effective in rapidly and completely occluding dentin tubules. The EDX and ESCA studies show that the dentin surface deposit and occluded tubule plug contain high levels of calcium and phosphate, as well as carbonate. CLSM has confirmed that the toothpaste and the desensitizing prophylaxis paste have the same mechanism of action, that the arginine and calcium carbonate components are both essential to the effectiveness of these products, and that the arginine becomes incorporated into the dentin plug. The hydraulic conductance studies demonstrate that the occlusion provided by the arginine-calcium carbonate technology results in highly significant reductions in dentin fluid flow, and that the tubule plug is resistant to normal pulpal pressure and acid challenge. CONCLUSION: A breakthrough technology based upon arginine and calcium carbonate provides clinically proven benefits with respect to rapid and lasting relief of dentin hypersensitivity. It is unique in that two of its key components, arginine and calcium, are found naturally in saliva, and that the arginine and calcium carbonate work together to accelerate the natural mechanisms of occlusion to deposit a dentin-like mineral, containing calcium and phosphate, within the dentin tubules and in a protective layer on the dentin surface.

Evaluation of side effects and patients' perceptions during tooth bleaching.

OBJECTIVE: The objective of this nightguard vital bleaching (NGVB) study was to compare tooth sensitivity (TS), gingival irritation (GIr), and other side effects, as well as patients' perceptions during tooth bleaching, from treatment with experimental 5 and 7% hydrogen peroxide (HP) bleaching solutions with those of a commercially available 10% carbamide peroxide (CP) product. MATERIALS AND METHODS: Sixty-one participants completed the study wearing a scalloped maxillary treatment tray without reservoirs with the different concentrations of bleaching gels for 30 minutes twice a day for 7 days. Parameters evaluated were changes in gingival index (GI), nonmarginal gingival index, nongingival oral mucosal index, and tooth vitality. Participants were seen pretreatment, after 7 treatment days, and 1 week post-treatment. A daily log form to record TS and GIr was completed by each participant as well as a sensitivity questionnaire at each appointment. Additionally, at 10 months post-treatment, a questionnaire was sent to the participants concerning TS and GIr relative to the treatment process. RESULTS: Data from end-of-treatment questionnaires, daily log forms, and clinical examination revealed a statistical difference (p < or = 0.05) in the patients' ranking of and days of TS and GIr between group S (7% HP) and group T (10% CP, control group) at the end of active treatment. There also existed a statistical clinical change in the GI levels for groups R and S compared with the control group T. There was no statistical difference (p > 0.05) in any of the parameters evaluated among the three products at 7 days or 10 months post-treatment. CONCLUSIONS: Participants in group S reported significantly more TS, GIr, and days of each compared with the control. There also existed a significant clinical change in the GI levels for groups R and S compared with the control group T. There was no significant difference among the three products at 7 days post-treatment. After ending treatment, TS/GIr was resolved in 2 to 3 days and did not recur during the 10 months post-treatment. CLINICAL SIGNIFICANCE: The experimental HP bleaching solutions, as described in this study, can be used in NGVB with no long-term side effects as evaluated in this study for up to 10 months post-treatment.

High levels of hydrogen peroxide in overnight tooth-whitening formulas: effects on enamel and pulp.

PURPOSE: Limited data are available to assess the safety of high levels of hydrogen peroxide in overnight tooth-whitening formulas. The purpose of this study was to assess the effects of hydrogen peroxide on enamel microhardness, pulp penetration, and enamel morphology. MATERIALS AND METHODS: Colgate Platinum Professional Overnight Whitening System (Colgate Oral Pharmaceuticals, Inc., Canton, MA, USA) (10% carbamide peroxide, equivalent to 3.5% hydrogen peroxide) was compared with two prototype formulations containing either 7.0% or 12.0% hydrogen peroxide. In the pulp chamber studies, human extracted teeth were exposed to 3.5%, 7.0%, or 12.0% hydrogen peroxide for 30 minutes, 4 hours, or 7 hours. Microhardness, electron spectroscopy for chemical analysis, and atomic force microscopy evaluations were made from enamel blocks cut from human extracted molars. The enamel blocks were evaluated following 14 7-hour treatments (98 h total). RESULTS: At 7 hours' post-treatment, hydrogen peroxide penetrated the pulp chamber at 23.12 +/- 10.09, 24.58 +/- 6.90, and 26.39 +/- 5.43 microg for 3.5%, 7.0%, and 12.0% hydrogen peroxide, respectively. With regard to enamel morphology, pulp penetration, microhardness, and elemental composition, no statistically significant differences were observed between treatment groups following 98 hours of treatment. CONCLUSIONS: Hydrogen peroxide does not adversely affect enamel morphology or microhardness. The levels recovered in pulp indicate that hydrogen peroxide is not expected to inhibit pulpal enzymes. CLINICAL SIGNIFICANCE: Overnight tray products containing levels of hydrogen peroxide of 3.5%, 7.0%, and 12.0% are not expected to adversely affect the enamel or pulpal enzymes. Additional safety studies are needed to assess the potential for tooth sensitivity and gingival irritation.