You can read the part 1 of most common disease that causes loss of teeth, before reading the 2nd part.
Bacterial Polysaccharides
The ability of S. mutans to initiate smooth surface caries and form large amounts of adherent plaque depends on its ability to polymerize sucrose into high-molecular-weight, dextran-like, extracellular polysaccharides (glucans). The cariogenicity of S. mutans depends as much on its ability to form large amounts of insoluble extracellular glucans as on its ability to produce acid.
Essential Properties of Cariogenic Bacteria
• Acidogenic
• Able to produce a pH low enough (usually pH < 5) to decalcify tooth substance
• Able to survive and continue to produce acid at low levels of pH
• Possess attachment mechanisms for firm adhesion to smooth tooth surfaces
• Able to produce adhesive, insoluble plaque polysaccharides (glucans)
Glucans enable streptococci to adhere to one another and to the tooth surface, probably via specific receptors. In this way S. mutans and its glucans may initiate their attachment to the teeth and enable critical masses of plaque to be built up. Production of sticky, insoluble, extracellular glucan produced by strains of S. mutans is strongly related to their cariogenicity. The importance of sucrose in this activity depends on the high energy of its glucose-fructose bond which allows the synthesis of polysaccharides by glucosyltransferase without any other source of energy. Sucrose is thus the main substrate for such polysaccharides. Other sugars are, to a variable degree, less cariogenic (in the absence of preformed plaque), partly because they are less readily formed into cariogenic glucans.
Plaque polysaccharides, synthesized by bacteria, play an essential role in the pathogenesis of dental caries. The proportions of the different types of polysaccharide, and the overall amounts formed, depend both on the kinds of bacteria present and the different sugars in the diet. On a sucrose-rich diet the main extracellular polysaccharides are glucans. Fructans formed from fructose are produced in smaller amounts. They are more soluble than glucans and less important in caries. Acid-producing microorganisms that do not produce insoluble polysaccharides do not appear to be able to cause caries of smooth surfaces. Even mutant strains of S. mutans which produce more soluble polysaccharides seem not to be cariogenic. Polysaccharides thus contribute to the adhesiveness, bulk and resistance to solution of plaque. In the past, lactobacilli were thought to be the main cause of dental caries because they are numerous in the saliva and can be isolated from carious cavities. They are also acidogenic.
However, they are present only in relatively small numbers in dental plaque until after caries has developed. In gnotobiotes, lactobacilli are weakly cariogenic but some can produce fissure caries where adherent plaque formation is less important. Overall there is little evidence that lactobacilli are clinically important in initiating dental caries but they may contribute to tooth destruction after the process has started. Many other microorganisms can also be found in plaque. The role of the many filamentous forms is not known. Strains of actinomyces are also found, particularly when caries is rampant, but appear capable only of causing root surface lesions.
Bacterial plaque. A decalcified section showing darkly staining plaque lying on enamel and within a carious cavity. The plaque has remained intact and adherent to the enamel throughout the processes to which the specimen was subjected in preparation for sectioning.
Though bacteria are responsible for acid production, bacterial plaque enables large concentrations of them to adhere to the teeth and, in stagnation areas, prevents effective buffering of bacterial acids by saliva. Important points about microbiological aspects of dental caries are summarized below.
Microbiological Aspects of Dental Caries
• Dental caries is a bacterial disease
• The organisms mainly responsible are specific strains of Streptococcus mutans
• The cariogenicity of S. mutans has been established by inoculating it into the mouths of otherwise germfree animals (gnotobiotes)
• The presence of S. mutans in the human mouth is associated with caries activity
• Other bacteria including lactobacilli and other strains of streptococci are only weakly cariogenic or are non-cariogenic despite being able to produce acid