Dental Caries: Microbiology and Contributing Factors Explained”

Dental Caries: Microbiology and Contributing Factors Explained”

Question. Defy dental caries. Describe microbiology and factors promoting dental caries.

Answer.

Microbiology Of Dental Caries

• In the pathogenesis of dental caries an important role play in cariogenic bacteria, i.e. oral streptococci, especially of group mutants and lactic acid bacteria (Lactobacillus spp.).
• It is believed that bacteria of the species Streptococcus mutans are the main factor that initiates caries and very important factor of enamel decay.
• The bacteria of the genus Lactobacillus are important in further caries development, especially in the dentin.
• Streptococcus mutans and lactobacilli are characterized by the ability to grow in an acid environment and the property of rapid metabolism of sugars supplied in the diet to organic acids, including lactic acid.
• The microbial community from dentinal lesions is diverse and contains many facultatively and obligately anaerobic bacteria belonging to the genera Actinomyces,
  Bifiobacterium, Eubacterium, Lactobacillus, Parvimonas and Rothia.
• Streptococci are recovered less frequently. Caries can also be caused by other bacteria, including members of the mitis, anginosus and salivarius groups of streptococci,Propionibacterium, Enterococcus faecalis and Scardovia.

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Streptococcus mutans

Streptococcus mutans are the most cariogenic pathogens as they are highly acidogenic, producing short­chain acids which dissolve hard tissues of teeth.

They metabolize sucrose to synthesize insoluble extracellular polysaccharides,which enhance their adherence to the tooth surface and encourage biofilm formation.

The reactions are catalyzed by three isozymes of glycosyltransferases.

The most important mutans streptococci isolated from tooth caries samples are S. mutans and S. sobrinus.

S. mutans is more cariogenic than S. sobrinus because of specific cell­surface proteins, which aid in its primary attachment to the tooth. S. sobrinus lacks such proteins.

S. mutans is able to metabolize a number of sugars and glycosides such as glucose, fructose, sucrose, lactose, galactose,mannose, etc.

In the presence of extracellular glucose and sucrose,S. mutans synthesizes intracellular glycogen­like polysaccharides (IPSs).

S. mutans produces also mutacins (bacteriocins), what is considered to be an important factor in the colonization and establishment of S. mutans in the dental biofilm.

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Streptococcus Sobrinus

S. sobrinus has been implicated in caries development particularly in instances where caries development appears to be independent of S. mutans.

Interestingly, S. sobrinus displays higher acid production and acid tolerance compared to S. mutans.

Lactobacilli

Among the Lactobacillus rods in the oral cavity occur: L. acidophilus, L. casei, L. fermentum, L. delbrueckii, L. plantarum, L. jensenii, L. brevis, L. salivarius and L. gasseri.

Lactobacilli are divided into two main groups: homofermentative which in the fermentation process of glucose produce mainly lactic acid, e.g.

Lactobacillus casei, Lactobacillus acidophilus, heterofermentative which in addition to lactic acid produce acetate, ethanol and carbon dioxide, e.g. Lactobacillus fermentum.

Lactobacilli are isolated from deep caries lesions but rarely just before the development of dental caries and in the early tooth decay.

It is believed that they are pioneering microorganisms in the caries progress, especially in dentin.

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Veillonella

It is a Gram­negative cocci which is commonly found in plaque.

It utilizes lactic acid by converting it to propionic acid and other weak acids.

Factors Promoting Dental Caries
Tooth Factors

• Tooth factors such as composition of tooth, structure of enamel, morphologic characteristics of tooth, position of tooth are the caries promoting factors.
• In composition of tooth surface enamel is more resistant to caries than subsurface enamel. This is because surface enamel is highly mineralized.
• Presence of deep, narrow occlusal fisures, buccal and lingual pits leads to the development of dental caries.
• Teeth which are malaligned, out of position, rotated or otherwise not normally situated are difficult to clean and favor accumulation of food and debris which lead to dental caries.

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Salivary Factors

• Salivary factors such as composition of saliva, pH, quantity, viscosity and antibacterial factors in saliva play role in promotion of dental caries.
• When salivary flw rate is normal it leads to cleaning of bacteria from tooth surface and reduces the chances of dental caries while in xerostomia incidence of caries is high.
• As viscosity of saliva is increased deposition of plaque increases because thick saliva does not produce proper cleaning action.
  If viscosity of saliva is decreased normal contents of mineral is less and saliva does not produce anticaries functions.
• As the buffering action of saliva is decreased acid demineralization of tooth by dental caries become high this is because low concentration of salivary bicarbonate does not cause neutralization of acids which is produced by cariogenic bacteria.
  • Salivary enzymes such as amylase leads to breakdown of starch (which is a residual carbohydrate) from tooth surface which is washed easily from mouth. As if levels of salivary amylase are too low this will lead to dental caries.
  • Certain antibacterial agents are found in saliva such as lysozyme, thiocyanate, etc. These agents leads to the destruction of cariogenic bacteria by anti­bacterial action and reduces caries incidence. As if defiiency of such agents is present this will lead to the promotion of dental caries.
  • Salivary immunoglobulins such as IgA and IgG inhibit S. mutAns by facilitating destruction process through phagocytosis and lead to decrease in dental caries. If salivary immunoglobulin levels are decreased this leads to the increase in dental caries.

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Diet Factors

• Diet factors such as physical nature, carbohydrates, vitamins and floride content play important role.
• More and more intake of soft and sticky food increases possibility of dental caries.
• Foods rich in carbohydrates lead to the dental caries.
• Physical nature of diet is important as soft refied foods cling to the teeth and are not removed because of lack of roughage. This collection of debris is due to reduction in mastication because of softness of diet. This leads to dental caries.
• Fluoride ions limit rate of carbohydrate metabolism by cariogenic bacteria and reduce acid attcks on tooth. Lagging of floride in diet leads to the increase incidence of dental caries.

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Dental plaque

• Dental plaque is the soft, non­mineralized bacterial deposit which forms on teeth and dental prosthesis that are not adequately cleaned.
• Plaque harbors cariogenic bacteria on tooth surface.
• Rapid production of high amount of acids in plaque occur through fermentation of carbohydrates by cariogenic bacteria.
• Plaque hold the acids on tooth surfaces for longer duration.
• Increased thickness of plaque does not allow salivary buffrs to enter into neutralize the acids produced by the cariogenic bacteria.