Dental caries biofilms

The presence of S. mutans and other cariogenic bacteria contributes towards the formation of a biofilm known as dental plaque, and their metabolism of fermentable carbohydrates in the diet leads to the formation of acids [12]. Dental caries has been described as a complex imbalance in physiologic equilibrium between tooth mineral and biofilm [13]. Biofilms imply the involvement of microbiological species [14], but the key concept included within this definition is that the bacteria involved are native to the body, not a group of specific invasive bacteria causing infection [14]. 

Dental caries is a common chronic disease in which contact between teeth, food, and bacteria is involved. The major bacteria involved are believed to be Streptococcus mutans and S. sobrinus, although several Other types of bacteria are involved. Three stages have been outlined in caries adherence of bacteria to the teeth, formation of glycocalyx due to synthesis of a sticky glucan by the action of the bacterial enzyme glucosyl transferase on sucrose, and accumulation of plaque, which is a biofilm. In the dental plaque, there is continuing acid production by the bacteria, which are able to metabolize carbohydrates in acid medium, and the acid demineralizes the enamel of the teeth. 

Robinson C, Kirkham J, Percival R, Shore RC, Bonass WA, Brookes SJ, Kusa L, Nakagaki H, Kato K, Nattress B A method for the quantitative site-specific study of the biochemistry within dental plaque biofilms formed in vivo. Caries Res 1997 31 194-200. 

Teeth adherent bacterial biofilms, commonly called plaque or plaques, are responsible for the common forms of periodontal disease (Chap. 13) and dental caries (Chap. 15). In children or adults who keep their teeth clean and have no periodontal disease, the bacteria in a biofilm (the microbiota) is mostly gram positive and resembles that in saliva or adhering to the oral mucosa. The microbiota is predominantly saccharolytic and the major fermentation... 

The salivary proline-rich proteins have a two-domain structure, a proline poorN-terminal domain that is acidic or basic and determines enamel binding, and a proline-rich C-terminal domain that determines bacterial binding. Individual variations in acidic proline-rich proline allelic composition and in the amount of salivary agglutinin, a secreted innate immunity protein that binds bacteria, may account for differences in biofilm composition and dental caries susceptibility. 

The probiotic strain E. faecium PR88 was studied in clinical trial (Allen et al. 1996). The consumption of this strain led to alleviation of the symptoms of irritable bowel syndrome in humans. The efficacy and safety of live combmedBifidobacterium, Lactobacillus and Enterococcus capsules in treatment of irritable bowel syndrome was also demonstrated (Fan et al. 2006). E. faecium functions as a probiotic strain inhibiting biofilm formation by Streptococcus mutants, which is an etiological agent for dental caries (Kumada et al. 2008). 

Dental calculi, i.e. calcifications of the dental plaque biofilm, contain various calcium phosphates, since these inorganic ions are provided by saliva or crevicular fluids. Although the pattern of calcification of oral microorganisms, either intra- or extracellularly, is mainly a characteristic of each bacterial species or strain [75], it may be influenced by nutritional factors, such as saliva proteins, as well [76]. The interactions of saliva with dental calculi and its role in preventing dental caries by controlling the enamel de- and remineralisation processes have been reviewed [19]. 

Bones and teeth dissolve in acid. The insoluble calcium monophosphate salt, from which hydroxyapatite is made, is converted to the more soluble calcium dihydrogen phosphate salt in an environment whose pH is less than 6.2 (Sect. 9.1.1). The severity of caries was related to the pH produced in dental biofilms (plaques) after ingesting sucrose and other sugars by Richard M Stephan. The pH response he identified is referred to as Stephan Curve. He found that the starting pH, the extent of its drop, and the time for recovery to the starting pH were all related to caries severity. The pH drop was later associated with lactic acid production due to bacterial carbohydrate fermentation (saccharolytic fermentation, Sect. 1.3.2). The subsequent rise in pH was due to the production of ammonia by bacterial... 

The permanence of bacterial plaque on the tooth surface will lead to loss of minerals constituents of the dental enamel, promoting the installation of the caries disease [42,43]. The carious lesion is characterized by the tooth structure (hydroxyapatite) di-mineralization by the production of organic acids, such as lactic acid, resulting from bacterial (dental biofilm) metabolism [42,43]. This results in loss of calcium and phosphate ions, which subsequently diffuse out of the tooth. In this complex process, the microorganism, particularly streptococcus species, have an important role in its etiology [43]. 

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