Flora of the oral cavity

The oral cavity is similar to other sites of the body in that it is colonized with ‘normal flora’ in a symbiotic relationship. Indeed, it has been estimated that the average human body is colonized by 10 times more bacteria than there are mammalian cells.The oral microflora is very diverse with over 500 species cultivable and many others not cultivable. The microbes of the oral cavity consist of bacteria, fungi, viruses, and occasionally protozoa. The diversity is related to varied habitats in the oral cavity with a variety of nutrients. Dental plaque associated with caries and periodontal disease has gradients of oxygen tension and pH that provide conditions for the growth and survival of a wide spectrum of bacteria. The large population of normal oral flora makes it difficult for invading pathogens to compete for nutrients and receptor sites. In addition, some bacteria produce antimicrobial substances to protect their habitat from invasion by other organisms. The microbial population and the surrounding environment are together known as the ecosystem. The establishment of microorganisms in a host is termed colonization. Permanent colonization in a symbiotic relationship results in the establishment of normal flora. If the normal flora is provided the right conditions and gain access to a normally sterile tissue such as the dental pulp or periradicular tissues, they become opportunistic pathogens. The host’s response to a microbial infection may be both non-specific inflammation and/or specific immunological reactions. An infection is produced if the invasion of microbes produces damage to tissue. A knowledge regarding the oral microflora may be beneficial in comprehending the pathogenesis of various oral disease conditions.