The oral microflora--friend or foe? Can we decide?

This paper discusses the factors that determine whether the oral microflora play a beneficial or detrimental role in the health of an individual during their life. The resident microflora of the mouth is diverse, and distinct from that found elsewhere in the body due to its unique biological and physical properties. This natural microflora is essential for the normal development of the physiology of the host, and contributes to the host defences by excluding exogenous micro-organisms. The oral microflora varies in composition on distinct surfaces (e.g. teeth, mucosa), and at sites on a specific surface (e.g. fissures, gingival crevice), demonstrating that subtle properties of a habitat influence the ability of individual species to colonise and dominate. The composition of these oral microbial communities remains relatively stable over time (microbial homeostasis). This stability does not indicate a passive relationship with the host, but reflects a dynamic balance among the component species. However, this stability can be perturbed by significant changes to the oral environment or in a person's life-style that occur during the life of an individual. Alterations in diet, medication, smoking, saliva flow, denture wearing, general health, etc, can lead to overgrowth by previously minor components of the oral microflora, which can predispose a site to disease. Likewise, the immune response can wane in old age, which may result in colonisation by exogenous and often pathogenic micro-organisms. Oral micro-organisms can also act as opportunistic pathogens, and cause serious disease elsewhere in the body. Therefore, active oral health care management is needed in order to maintain microbial homeostasis throughout life to ensure that we reap the benefits of our resident oral bacteria and not suffer from their mischief.