Oral Microflora

Oral microflora looks at the complex community of various microorganisms present in the oral cavity.These microbes are acquired shortly after birth and colonize the entire mouth to form resident populations.

The resident oral microflora represents the natural endogenous bacteria species found in the various different microhabits in the mouth. The colonization by the microflora inhibits the infection of foreign pathogens, which serves to maintain a healthy balance in the oral cavity. In normal healthy states, this is beneficial to the individual. However, opportunistic infections can take place if the balance between the microflora and the host defences is upset. This leads to diseases such as the formation of caries.

Specific Plaque Hypothesis

The Specific Plaque Hypothesis attempts to explain the pathological effects of plaque formation in the oral cavity.

Plaque formation is caused by the colonization and multiplication of microbial species in the oral cavity. The Specific Plaque Hypothesis proposes the concept that out of the diverse microflora found in the oral cavity, only specific species are responsible for the formation and aggravation of oral cavities.

However, as more researches are being conducted, it is becoming evident that specific pathogens alone are not capable of caries formation. A myriad of factors contribute to the complexity of caries formation and this diminishes the validity of Specific Plaque Hypothesis in explaining caries formation. Currently, the widely accepted view of caries formation is proposed by the Ecological Plaque Hypothesis, a hypothesis that was build upon the foundation of Specific Plaque Hypothesis. It is important to note that while the Specific Plaque Hypothesis is slowly being proven to be obsolete, its role in assisting us with the understanding of plaque formation cannot be deemed insignificant.

Ecological Plaque Hypothesis

As more research is done, the Specific Plaque Hypothesis and Non-Specific Plaque Hypothesis evolved to support the development of the Ecological Plaque Hypothesis, which combines key points proposed by both the Specific Plaque Hypothesis and Non-Specific Plaque Hypothesis. The Ecological Plaque Hypothesis proposes that a change in the conditions of the oral environment, which affects both the quality and quantity of specific bacteria, such as Mutans Streptocci and Lactobacilli, in the oral cavity, will enhance demineralization and aid in the production of caries. Prevention of caries could thus be done by measures which aid in controlling the effects felt by the microflora community when there is a change in oral cavity conditions. This allows the ideas proposed by the ecological plaque hypothesis to help in the development of new approaches to the prevention of caries and periodontal diseases, such as replacement therapy.

Dental Biofilms

Dental biofilms are a diverse microbial community found on the surface of the enamel of our teeth. Their formation begins with a pellicle formation made up of proteins, followed by the subsequent colonization of bacteria. While it might be difficult to understand everything about these microbial communities, it is important to know that their existence, while involved in many pathological oral diseases (due to carries causing bacteria), is actually of much benefit to the host at the early stages of development as they provide the teeth with a layer of protection that cannot be matched. These biofilms employ a great deal of inter-cell communication to not only keep themselves alive, but also to protect the host.

Microbiology of Enamel Caries

The microbiology of enamel caries mainly involve aciduric and acidogenic bacteria such as mutan streptococci and lactobacilli. Such bacteria are able to survive and thrive in acidic conditions and metabolise polysaccharides, producing acid that demineralize the surface of the enamel, leading to enamel caries. Although recent studies have shown that other bacteria are also involved in enamel caries formation, these two bacteria play a vital role in the process caries initiation. Furthermore, although there is remineralization of enamel, areas of caries will leave a scar on the enamel surface due to complex salivary processes.

Microbiology of Root Caries

The study of the microbiology of root caries aims to draw conclusions and predict trends between the presence of certain types of bacteria and its propensity to induce root caries. However, as an increasing number of tests are being done, it is proven that the microflora is constantly evolving and is both diverse and extensive. Many scientists have been able to prove that, generally, the presence of Mutans Streptococci and Lactobacilli are predictive of carious root lesions. It is important to note that the microflora differs from each individual, and it is not possible to pinpoint any causative agents.


The general principle behind probiotics is bacteriotherapy i.e. the replacement of cariogenic strains of bacteria such as S. mutans with similar strains that are harmless. Commonly used bacteria are Lactobacilli, Streptococci and Bifidobacteria. The coaggregation of the cariogenic bacteria to the probiotic strain inhibit the cariogenic bacteria, hence reducing the occurrance of caries.


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