Normal Oral Microbiome

 The human oral cavity is normally populated by a diverse array of microorganisms (Kilian et al., 2016). These commensal bacteria have evolved with us to develop a mutually beneficial ecosystem.
      
Role of Oral OrganismsThe role these organisms play under normal physiological conditions can include the proper development of the host’s innate and adaptive immune system, the breakdown of metabolites into compounds that are more easily processed by humans, the breakdown of environmental toxins, maintenance of the mucosal barriers in the mouth, and preventing the introduction of more pathogenic species.
    Manner of Operation
    The oral microbial ecosystem operates in a delicate balance with the host’s immune system by maintaining an equilibrium between anti-inflammatory and inflammatory signals (Iwasaki & Medzhitov, 2015). Because of this balance, and the native microbes’ abilities to prevent the rapid growth of new foreign microorganisms, primary infection of the oral tissues is not a common occurrence.
    
    However, changes in the body’s homeostasis, such as occurs during hormonal changes during aging or due to other illness or environmental factors can alter the normal balance (Rosier, De Jager, Zaura, & Krom, 2014).
    
    This can allow previously benign organisms to opportunistically take over and cause infection, or this can allow foreign fungi or bacteria to take root and cause disease.

    Microbiome Subdomains

The microbiome of the mouth is further complicated by the distinct subdomains formed in different regions including the teeth, gingival sulci, tongue, hard palate, and cheek tissues.

Recent surveys of the oral microbiome identified an average of 296 distinct bacterial species per person (Kilian et al., 2016). In order to maintain equilibrium between the host and their oral microbiota, the innate and adaptive immune systems provide formidable defenses