Lynette Zaidel

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.

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.