Microbial plaque

Microbial plaque is the primary cause of both deutal caries and periodontal disease [134,135]. In principle, most plaque can be ranoved using appropriate oral hygiene devices, such as toothbrushes aud dental floss, but in practice many patients lack both the skill and the motivation to maintain a reliable plaque-free state [136]. For this reason, professional dental prophylaxis has an important part to play in helping maintain sound oral health in individuals. The primary function of such prophylaxis is ranoval of plaque, stain and calculus [137] and elimination of the factors that cause plaque to build up and be retained [138]. This may be augmented by the topical application of fluoride in an appropriate form. 

The addition of therapeutic or cosmetic agents to dentifrices has paralleled advances in knowledge about factors affecting the human dentition. Agents added to dentifrices can act directly on the host tooth stmcture or on specific oral accumulations, for example, the principal action of fluoride is on the tooth enamel. The primary action of an abrasive, however, is on an accumulated stained pellicle. Oral accumulations of interest to preventive dentistry are dental pellicles, dental plaque, dental calculus (tartar), microbial populations responsible for oral malodor, and oral debris (food residues, leukocytes, etc). Plaque is most important because of its potential to do harm. 

Once microbes have multiplied and established themselves as a colony, they can adhere to metal parts forming microbial plaquesUnderneath these plaques, severe corrosion of metal is often found. 

Marsh, P. D. 1995. Dental plaque. In Microbial Biofilms (H. Lappin-Scott and J. W. Costerton, Eds.), Plant and Microbial Biotechnology Research Series 5, pp. 282-300. Cambridge Univ. Press, Cambridge, UK. 

One of the early enthusiasts of microscopy was Antoni van Leeuwenhoek. During the sixteenth century he constructed over 500 single lens microscopes. While crude by today s standards, van Leeuwenhoek s microscopes revealed an array of microbial life. For example, his descriptions of organisms found in lake water were the first observations of the green algae called Spirogyra and another microbe that came to be known as Vorticella. Finally, his observation of animacules in tooth plaque was the first visual detection of bacteria. 

Formation of the acquired salivary pellicle is the result of biopolymer adsorption at the tooth-saliva interface. The term acquired pellicle was first suggested in a review of the nomenclature of the enamel surface integuments by Dawes et al. [1], to describe the cuticular material formed on the enamel surface after eruption. The pellicle consists of adsorbed proteins and other macromolecules from the oral environment (saliva, crevicular fluids) and is clearly distinguished from the microbial biofilm (plaque) (fig. 1). 

The rhizosphere is home to a diverse microbial community, including aerobic heterotrophs (Gilbert and Frenzel, 1998), methane oxidizers (Bosse and Frenzel, 1997 Calhoun and King, 1997), and ammonium and nitrite oxidizers (Bodelier et al., 1996 Arth et al., 1998). Microscopy has also shown that microbial cells are associated with Fe plaque (Trolldenier, 1988 St-Cyr et al., 1993), but visual examinations alone cannot determine if cells are responsible for plaque formation. Trolldenier (1988) demonstrated that rusty-colored colonies formed when root plaque was inoculated into an iron-containing medium, but further characterization of these colonies was not attempted. 

As mentioned previously, it has long been assumed that the dominant route of Fe plaque formation is via chemical rather than biological pathways. In part, this is due to potentially rapid rates of chemical Fe oxidation under circumneutral conditions (see above). Although microbial cells were observed embedded within the Fe plaque (Trolldenier, 1988 St-Cyr et al., 1993), it was assumed that these cells... 

Given the abundance of Fe in soils, the variety of mineral forms that it may take, and the complex interactions of those mineral forms with other metals, Fe minerals often play an essential role in the overall control of metal interactions in the soil. This is especially true in the rhizosphere, where as discussed above, microbially mediated cycling of Fe between oxidized and reduced forms can be rapid. Wetland plants can increase metal sequestration by driving the formation of Fe plaque, particularly in tidal wetland soils, where burial is rapid. The binding of metals to Fe plaque in the rhizosphere is one reason that wetland plants have been investigated for the phytoremediation of metal-contamuiated sites (Weis and... 

Analysis of the Pb EXAFS data from the Fe-plaque revealed a Pb-0 interatomic distance of 2.4 A, which is inconsistent with published data for Pb sorbed to Fe-oxides (-2.27 A). Furthermore, optimized fitting of the second shell EXAFS function was obtained for C or N at a distance of 3.4 A, which is longer than previous reports for Pb bound humic material (Hansel et al. 2001). Based on fits that included a sample where Pb was bound to microbial biofilm it was concluded that the Pb was bound to a microbial biofilm-like material apparently intimately associated with the Fe-plaque. This finding demonstrates the important role of microorganisms in rhizosphere processes and the preferential binding of Pb to extracellular polymeric substances even in the presence of a highly reactive high surface area Fe-oxide phase. 

Such a dentifrice was used in a 6-month double-blind study to determine its effect on the microbial composition of dental plaque as compared to an identical dentifrice without essential oils. Supragingival plaque and saliva samples were collected at baseline and their microbial content characterized, after which the study was conducted for 6 months. The essential oil dentifrice did not signi cantly alter the microbial ora, and opportunistic pathogens did not emerge, nor was there any sign of developing resistance to the essential oils in tested bacterial species (Charles et al., 2000). 

Charles, C. H., Vincent, J. W., Borycheski, L. et al. 2000. Effect of an essential oil-containing dentifrice on dental plaque microbial composition. Am. J. Dent. 13 26C-30C. 

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