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Browsing by Subject "Oral Biofilms"

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    The Interfacial Integrity Of Dental Restorations: Exploring The Effect Of Oral Biofilms, Mechanical Challenges, And Antimicrobial Treatments
    (2016-05) Carrera Vidal, Carola
    Better tools to study the interfacial integrity of dental composites and the factors associated with its eventual breakdown are needed. The initial work focused on the optimization of techniques to study leakage and bond strength. We developed a method for 3D quantification of leakage around dental restorations by using silver nitrate infiltration, micro-CT and image subtraction, overcoming previous limitations of this technique. Also, a new variant of the Brazilian Disk Test specimen was developed for testing dentin-composite bond strength. This novel test provided several advantages including: zero premature failure, simpler testing procedures, a consistent failure mode involving the adhesive interface, and reduced variation in the measurements. We also developed a model to investigate the role of oral biofilms on the degradation of the adhesive interface. Our results suggested that oral biofilms in the presence of sucrose led to active degradation of the adhesive interface. Furthermore, we studied the combined effect of mechanical and biofilm challenge on the interfacial integrity of dental restorations. The results showed that when specimens are subjected to both challenges, a greater reduction in fracture strength is seen compared to the effects of fatigue and biofilm alone, demonstrating the additive effect of both. Again, the presence of biofilm showed a substantial effect in the degradation of the adhesive interface, which was significant in the presence of sucrose. The effect of fatigue was much less pronounced. Antimicrobial containing adhesives are used to prevent the breakdown of the adhesive interface. In the final part of this project, a multispecies oral biofilm/culture model was developed to test the effectiveness of commercially available MDPB-containing adhesive system. We found that the polymerized antimicrobial adhesive reduced biofilm formation and metabolic activity when tested in a closed multispecies biofilm model; however complete inhibition of oral biofilm formation was not observed. The presence of sucrose in the media abolished the antimicrobial effect seen under basal growing conditions. In addition, the polymerized MDPB-containing adhesive failed to inhibit multispecies oral biofilm formation in the absence and presence of sucrose when tested in a Drip Flow Reactor.
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    Polyphosphate-accumulating Bacteria: Potential Contributors to Mineral Dissolution in the Oral cavity
    (2017-05) Breiland, Ashley
    The role of oral bacteria in the dissolution of dental enamel and dentin that can result in carious lesions has long been solely ascribed to metabolic acid production. However, other microbial processes may also influence tooth dissolution. Recently, bacteria that accumulate polyphosphate in marine sediments have been shown to dynamically influence the solubility of phosphatic minerals. Here we show, using microscopy and genomic databases, that dental plaque and caries lesions, all contain abundant polyphosphate-accumulating bacteria. Using a culture of the model organism, Lactobacillus rhamnosus, a known polyphosphate-accumulating bacteria that is known to inhabit advanced caries lesions, we show that polyphosphate accumulation can lead to undersaturated conditions with respect to hydroxyapatite under some, but not all, oral cavity conditions. Samples of L. rhamnosus grown in various environmental conditions, including exposure to changing oxygenation conditions, input/removal of organics and trace nutrients, were collected over a course of 24 hours and stained with 4',6-diamidino-2-phenylindole (DAPI) to confirm/deny the presence of poly-p in the cells. A comparison of changes in extracellular inorganic phosphate between cultures grown under conditions that result in polyP accumulation vs conditions that did not, was used a a means of measuring the phosphate fluctuation that was likely contributed by intracellular phosphate accumulation. We suggest, through an extrapolation from our model organism results, that polyphosphate-accumulating bacteria, which we observed to be ubiquitous in oral fluids, have a similar influence on the solubility of minerals that comprise the tooth structure. These results suggest that the generation of undersaturated conditions by polyphosphate-accumulating bacteria constitutes a new potential mechanism of tooth dissolution that may augment the effects of metabolic acid production.