Modification of Acid Attack on Enamel Surfaces in vitro by Aggregations of Bacteria

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Abstract
When enamel is exposed to dilute lactic acid in vitro the surface of the tissue is rapidly etched, unlike that seen in caries. Experiments have been carried out to see whether enamel surface deposits, produced by bacteria in vitro, could modify simple acid attack on the tissue. Results show that by growing deposits of dextran-producing strains of Streptococcus sanguis and Streptococcus mutans on the surface of teeth prior to exposure to buffered lactic acid, the pattern of acid attack can be modified. Control teeth show demineralization of the outer surface layer after the formation of the ‘plaque-like’ deposits. Removal of the microbial deposit and exposure to buffered lactic acid results in loss of surface tissue and subsequent cavitation. However, after exposure of experimental teeth, having surface deposits, to buffered lactic acid in vitro lesions are produced that demonstrate well-mineralized surface zones superficial to demineralized subsurface regions. Quantitative imbibition studies have demonstrated that the initially demineralized surfaces produced by ‘plaque’ formation show an increase in mineral content after subsequent lesion formation. Attempts have been made to produce similar effects with other micro-organisms and also to alter the effects produced by treating the microbial deposits with the enzyme dextranase prior to acid exposure.

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