The buccale puzzle: The symbiotic nature of endogenous infections of the oral cavity.

The indigenous, 'normal', microflora causes the majority of localized infectious diseases of the oral cavity (eg, dental caries, alveolar abscesses, periodontal diseases and candidiasis). The same microflora also protects the host from exogenous pathogens by stimulating a vigorous immune response and provides colonization resistance. How can a microflora that supports health also cause endogenous oral disease? This paradoxical host-symbiont relationship will be discussed within the dynamic of symbiosis.Symbiosis means 'life together' - it is capable of continuous change as determined by selective pressures of the oral milieu. Mutualistic symbiosis, where both the host and the indigenous microflora benefit from the association, may shift to a parasitic symbiosis, where the host is damaged and the indigenous microflora benefit. Importantly, these are reversible relationships. This microbial dynamism, called amphibiosis, is the essential adaptive process that determines the causation of endogenous oral disease by a parasitic microflora or the maintenance of oral health by a mutualistic microflora.Complex microbial consortiums, existing as a biofilm, usually provide the interfaces that initiate and perpetuate the infectious assault on host tissue. The ecology of the various oral microhabitats is critical for the development of the appropriate selecting milieux for pathogens. The microbiota associated with dental caries progression is primarily influenced by the prevailing pH, whereas periodontal diseases and pulpal infection appear to be more dependent on redox potential. Candidiasis results from host factors that favour yeast overgrowth or bacterial suppression caused by antibiotics. Oral health or disease is an adventitious event that results from microbial adaptation to prevailing conditions; prevention of endogenous oral disease can occur only when we realize that ecology is the heart of these host-symbiont relationships.