Oral Microbiome and Oral Health Problems

Oral Microbiome and Oral Health Problems

Oral Microbiome/Oral Microflora

At birth oral cavity or the mouth is sterile but with time it becomes a complex accessible microbial ecosystem. The microorganisms found in the human oral cavity have been referred to as the oral microbiome. It is the second largest microbial community in the body. It becomes the home for 700 identified species of bacterial species, to which may be added protoza, yeast and mycoplasma.  Their distribution vary quantitatively and qualitatively according to the habitat. Streptococcus mutans, Streptococcus cricetus, Strptococcus rattus and Streptococcus sanguis are found in larger numbers on teeth, while Strptococcus salivarious is isolated mainly from the tongue. Bacteria present in oral cavity belongs to both aerobic and anaerobic and they can be either Gram negative or Gram positive bacilli or cocci. However, dominant members of the oral microbiome can also be found in fewer numbers at other body sites, such as the skin, gut and body fluids. 

There are different surfaces for microbial colonization like teeth, gingivae, tongue, throat and oral mucosa.  Streptoccus mutants has been shown to be the most important organism in initiate dental caries.  This capability is because of its ability to ferment sucrose to lactic acid via mixed acid fermentation pathway and and to survive in that low pH which is required for demineralization of the tooth. This organism can also attach to the pellicle coated enamel surface. These properties help the S. mutants in attaching and accumulating on tooth surface in the plaques.  

A large number of Gram negative bacteria are present in the oral cavity. Veillonella are the most numerous of Gram negative bacteria and it is a cultivable flora on saliva and on the surface of the tongue.  Veillonella are Gram-negative bacteria anaerobic cocci. Anaerobic Gram negative bacilli constitute another important group. Five genera of these bacteria have been frequently seen in oral cavity. These are Bacteroides, Fusobacterium, Leptotrichia, Wolinella and Selenomonas. 

Physicochemical factors affecting for oral microbiome

The physicochemical factors results from the combine action of host, microbiol and external factors. In in-vivo and in-vitro systems. the growth of microorganisms is influenced by five important variables. 

As the mouth is always bathed by saliva and crevicular fluid, water is not considered to be a limiting factor. 

The pH of an environment affects microorganisms and microbiol enzymes directly and also influence the dissoltion of many molecules that influence microorganisms. Usually microorganisms unable to tolerate extreme pH values. In the oral cavity the pH is maintained nearly neutrality (6.7-7.3) by saliva. The saliva contributes to maintenance of pH by two mechanisms. First the flow of saliva eliminates carbohydrates which could be metabolized by bacteria and removes acid produced by them. Secondly, the acidity from drinks and foods as well as from bacterial activity is nutralized by buffering activity of saliva. Bicarbonate and phosphate are involved. So, the pH is an important parameter for oral microbiota. Frequent sugar intake flavors the growth of acidic bacteria such as Lactobacillus and S.mutants

In oral cavity, microorganisms living in on extremely favourable environment which having the access to nutrients from both saliva and diet origin. Saliva is an important source of nutrients and can sustain normal growth of microorganisms. Saliva contains water, carbohydrates, proteins, glyco-proteins, amino acids, gases and several ions (such as Na, K, Ca, Cl and etc)   

Dental Plaque

Dental plaque means the complex microbial community found on the teeth surfaces, embedded in a matrix of polymers of bacterial and salivary origin, Tenaciously adhered and can’t be rinsed away. Dental plaque can remove with brushing. But if we don’t remove plaque properly, after 48 hours of formation it become calcified and unable to remove from tooth brushing. These are called calculus. Complex plaque begins to develop on a clean tooth surface after 4-6 hours.

Dental Caries

This is the most common dental disease. Dental caries is a microbial disease of calcified tissues of the teeth characterized by localized demineralization of the hard tissues (enamel,dentine,cementum) of the tooth by the acids produced by bacterial fermentation of dietary sugars and destruction of organic substance of the tooth(collagen is decomposed by bacterial proteases).
It results from the shift in the balance of the resident plaque micoflora. With excess sugar intake increased acid production and pH drop in the oral cavity.in low pH balance shifts cause Streptococcus mutans, Lactobacilli species to become predominant. Strptococcus mutans is a initiator for demineralization of teeth and Lactobacilli, Actinomyces spp enhances the progression of caries.This occur below pH 5.5. Time to time pH drop with sugar intake increase the caries risk.

Stages of caries development.

  1. Initial subsurface demineralization(reversible).
  2. Extention of demineralization zone towards dentine(irreversible).
  3. Collapse of surface layer to form a cavity.
  4. Extension of caries into dentine.
  5. Extension of caries into pulp.

Prevention of dental caries.

  • Minimize intake of fermentable carbohydrates (chocolates,biscuits,short eats.)
  • Stop intermittent consumption of sugary foods.Limit the intake to main meal times.
  • Brush teeth properly twice a day after breakfast and dinner with fluoridated toothpaste.


Article By,

Pasindu Chamikara – Microbiologist 

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