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Dental Caries: Resistance Factors — Fluorides
Published in Lars Granath, William D. McHugh, Systematized Prevention of Oral Disease: Theory and Practice, 2019
Stephen H. Y. Wei, Jan Ekstrand
Dental caries is a dynamic process involving the demineralization and remineralization of the dental tissues depending on whether the oral environment favors acidogenesis or remineralization.48 It is increasingly recognized that fluoride exerts a potent effect on the rate of remineralization and this may be one of the most important mechanisms of action of fluorides, particularly in low concentrations.49,50 There is abundant evidence that remineralization occurs naturally and has been seen clinically and microscopically by the presence of crystals of remineralization and histologically by the repair of artificial or natural white spot lesions with synthetic calcifying fluids or with saliva.51 Studies have indicated that even very low levels of fluoride in the oral fluids are sufficient to exert a profound effect. For example, the work of ten Cate and Duijsters50 has shown that 1 ppm of fluoride in a demineralization solution results in a dramatic reduction in the degree of demineralization. Increasing the fluoride concentration from 1 to 15 ppm appears to give additional benefits because of the formation of CaF2. The relationship between fluoride and pH on the degree of de- and remineralization is clearly demonstrated in Figure 5.50
Natural Algal Photobioreactors for Sustainable Wastewater Treatment
Published in Gokare A. Ravishankar, Ranga Rao Ambati, Handbook of Algal Technologies and Phytochemicals, 2019
D. M. Mahapatra, N. V. Joshi, G. S. Murthy, T. V. Ramachandra
Wastewater comprises of organic matter (degraded/partially degraded/inert), particulate/dissolved nutrients/minerals, heavy metals, xenobiotic compounds, pharmaceuticals and emerging contaminants. Various strategies have been employed for removal of nutrients through application of pond systems. For nitrogen (N), the main pond process involved is ammonia volatilization (Kayombo et al., 2010) that often occurs when there is a significant increase in the pond pH due to high photosynthesis. The other processes for N removal comprise of sludge sedimentation, nitrification, de-nitrification, ANAMMOX, etc. (USEPA, 2011; Mahapatra et al., 2013b). The algal ponds have been very efficient in the removal of N as observed in our earlier studies (Mahapatra et al., 2013b; Ramachandra et al., 2016, 2017a, b, c, 2018). Various design configurations have also aided in rapid nutrient removal as in case of the combined pond systems with wetlands that are usually called hybrid systems (Yeh et al., 2010; Ramachandra et al., 2016, 2017a, b, c, 2018). The high rate advanced algal facultative pond systems have also shown higher nutrient removal rates at relatively low HRT (Nurdogan and Oswald, 1995; Veenestra et al., 1995; Veeresh et al., 2010; Craggs et al., 2012). One of the major challenges in the treatment of wastewater is the heavy metals that have very dangerous impacts both on the environment and to human health (Ogunfowokan et al., 2008). Pond systems largely benefit in reducing the concentrations of heavy metals such as Cu, Cr and Ni from pulp and paper mill effluent (Achoka, 2002); Zn and Fe (Batty et al., 2008); Co and Cr (IV) from textile mill effluent (Mona et al., 2011); Pb from industrial w aste (Banerjee and Sarker, 1997) and Al and Ni from acid mine drainage (Kalin and Chaves, 2003). Ponds have been also responsible of higher organic matter removal especially through the initial anaerobic zone or anaerobic pond systems. This has been also accomplished in facultative pond systems where the organic matter is removed in two stages, i.e. a first stage where the organic matter is broken down to soluble organics, carbon dioxide and dissolved mineral nutrients by the bacteria action, and during the second stage the dissolved organics, carbon dioxide and nutrients are taken up by the algal communities. This produces oxygen that is again taken up by the heterotrophic bacteria for decomposition of organic matter, and this cycle repeats. Whereas under high organic loading, in the anaerobic stage, hydrolysis, acidogenesis, acetogenesis and methanogenesis takes place, which converts the bulk of the organic matter to methane, carbon dioxide and water (Chanakya et al., 2012). Just after such processes, the predominance of heterotrophic bacteria and algae increases due to increased mineralization and availability of dissolved soluble nutrients. Various studies have reported treatment of poly aromatics such as PCBs and dissolved organic matter through pond processes (Musikavong and Wattanachira, 2007; Badawy et al., 2010). The pond systems have also demonstrated their utility in treatment of other xenobiotic compounds such as pesticides (Ahmad et al., 2004), pharmaceuticals (Spongberg et al., 2011) and emerging pollutants such as hormones like estrogen (Gomez et al., 2007).
Effects of the green tea catechin epigallocatechin-3-gallate on Streptococcus mutans planktonic cultures and biofilms: systematic literature review of in vitro studies
Published in Biofouling, 2022
Maria Gerusa Brito Aragão, Carolina Patrícia Aires, Silmara Aparecida Milori Corona
All included records were published between 1989 and 2021. Twelve out of the fourteen selected studies only evaluated the effects of EGCG on planktonic cultures of S. mutans, while the biofilm counterpart was analyzed only by two of the selected publications. Six out of the 14 studies reported effects on S. mutans susceptibly. Growth curve, CFU counting, and aggregation assay were the most used methods to analyze the effects of EGCG on S. mutans viability, which was evaluated by 6 out of the 14 selected publications. The effects of EGCG on S. mutans acidogenesis were investigated by 3 out of the 14 selected studies. Moreover, the effects of EGCG on S. mutans virulence factors were reported by 3 out of the 14 selected references, which analyzed the effects of EGCG on soluble and insoluble polysaccharides, gtf B, C, and D genes, and on GTase activity. The two studies that evaluated the effects of EGCG on S. mutans biofilm used the crystal violet assay to analyze the percentage of biofilm reduction.
Effect of water aging on the anti-biofilm properties of glass ionomer cement containing fluoro-zinc-silicate fillers
Published in Biofouling, 2020
Traithawit Naksagoon, Tatsuya Ohsumi, Shoji Takenaka, Ryoko Nagata, Taisuke Hasegawa, Takeyasu Maeda, Yuichiro Noiri
Even though the mechanical properties were unchanged, the reason for progressive biofilm formation after water aging can be explained by the experimental conditions applied. The flow-cell system used in this study maintained the pH in the chamber at 7.0 even after 24 h, meaning that the continuous flow of fresh medium prevented bacterial acidogenesis as well as retention of released ions. Although the biofilm base was supposed to be maintained under acidic conditions, the antimicrobial effect was not enhanced.
The rumen microbiome: a crucial consideration when optimising milk and meat production and nitrogen utilisation efficiency
Published in Gut Microbes, 2019
Chloe Matthews, Fiona Crispie, Eva Lewis, Michael Reid, Paul W. O’Toole, Paul D. Cotter
A recent study suggested that methane production can, however, be reduced substantially without adverse effects on fibre digestion.84 The authors examined the effects of methane inhibition in the rumen of steers. The animals were fed either a hay:roughage diet or a hay:concentrate diet at a ratio of 60:40. An anti-methanogenic compound was also included, in this case, and in many others, chloroform. Results showed that with increasing levels of chloroform, there was an increase in H2 expelled and CH4 production decreased. Figure 3 illustrates the degradation of plant fibre from the hydrolysis of polysaccharides, releasing monomers. The monomers are then fermented through acidogenesis, resulting in the production of organic and short chain fatty acids. Hydrogen and CO2 are also formed and are used by methanogenic archaea to produce methane. Animals on the hay only diet showed a more efficient redirection of H2 into other microbial products in comparison to hay:concentrate diet. Metabolomic studies showed that there was an increase in the levels of amino acids, organic and nucleic acids found in the liquid phase of the rumen contents in both diets when methanogenesis was inhibited. This suggests that there may be enhanced microbial protein synthesis under these conditions. These changes showed an obvious alteration in the rumen microbiota, with an increase in the ratio of Bacteroidetes and Firmicutes and a decrease in Archaea and Synergistetes. However, there were no significant changes observed in the abundance of protozoa, fungi or fibrolytic bacteria, meaning that fibre degradation was not affected.84 The conclusion was made that, although there was a 30% decrease in methane production, this did not negatively affect rumen fermentation and fibre degradation, and the microbes were able to adapt and redirect H2 to produce other end products. Further supplementation may be needed in order to drive excess H2 and improve the energy supply to the animal.84 Although it had been believed that without the formation of methane, the rumen microbiota would be drastically affected, this study shows that it can adapt to changes in H2 flux and produce different end products without the need to produce methane, in turn reducing methane eructed by the host animal.