Nutritional determinants of the ecology of the oral flora.

Consideration of nutritional factors as determinants of oral microbial ecology leads to the conclusion that endogenous factors play a dominant role. It is the interactions between specific microorganisms and nutritional and other factors provided by the host that selectively determine the kinds of microorganisms which willinitially reside in the oral cavity and the sites which they will colonize. The persistence of these original "colonists" in their respective ecologic niches will depend in part on the accessibility of endogenous nutrients variously provided by saliva, tissue exudates, crevicular fluids, or degenerating host cells. It will also depend on their response to and interaction with microorganisms which immigrate to that site subsequently. The microbial ecology of a given site is therefore rarely uncomplicated, the notable exception occurring at the most microscopic level where one may encounter microcolonies of individual species within more heterogenous populations of microorganisms. The extent of this heterogeneity quantitatively and qualitatively is a reflection of the degree to which the interactions between the resident flora and the new arrivals, plus the local environmental changes which they both generate, serve to promote or to discourage the survival and growth of the individual species. This element of heterogeneity in a dynamic system with its inherent potential for variation makes it possible for relatively minor changes in local environmental conditions to result in significant differences in the microflora between one site and another even though they may be in close proximity to each other. Once this concept is appreciated it becomes easy to understand how disease processes such as dental caries may affect specific areas of a tooth while nearby areas are unaffected. The effects of exogenous nutrients on the ecology of the oral microbiota, nevertheless cannot be ignored. The diet may modulate such endogenous factors as the salivary secretions and the local resistance of the gingival tissues to infections. Although at our present state of knowledge the direct influence of dietary proteins and fats on the oral microbiota is thought to be of relatively minor consequence, dietary carbohydrates are of major ecological significance. Dietary sugars provide readily available substrates for the oral microorganisms, most of which depend on carbohydrates for energy sources. The metabolism of dietary sucrose by S. sanguis and S. mutans with the productions of acids and intracellular and extracellular polysaccharides has specific influence on the microbial composition, metabolic activities, and mass of coronal plaque. The ready availability of dietary carbohydrates undoubtedly influences the microflora of other parts of the oral cavity as well, eic species or indirectly through the interactions of other organisms with them...