Why do sugary foods promote dental caries?

By promoting the growth of bacteria and lowering the pH of mouth.

Explanation:

Sugar helps the bacteria to grow rapidly in the mouth as the two main bacteria Streptococcus mutans and Streptococcus sorbrinus thrive on sugar as a food source and form dental plaques.The formation of the dental plaque makes the pH of the mouth lower and thus, paves way for cavity formation due to demineralization of the teeth and destruction of the enamel.In this way, sugary foods promote dental caries.

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