In some circumstances the addition of strong dietary food acids, or even refluxed gastric acids, will exacerbate the problem. Strong dietary acids are available from a variety of extrinsic sources such as carbonated soft drinks, sports drinks, cordials and fruit juices. Frequent or prolonged exposure to these can lead to rapid demineralisation and can turn mild caries into a rampant attack.
A high frequency of exposure to dietary acids in the form of soft drinks, sports drinks, and fruit juice can shift the supragingival oral flora toward aciduric microorganisms. As the intra-oral pH falls, the numbers and proportions of S. mutans and Lactobacilli increase, and the proportions of acid-sensitive species such as Fusobacterium nucleatum, Streptococcus gordonii and Streptococcus oralis will fall. Thus, the fall in pH not only enhances the competitiveness of cariogenic organisms, but inhibits the growth and metabolism of non-caries-associated species. Chemostat studies of plaque bacteria have shown that certain species other that mutans streptococci or lactobacilli are competitive at pH values low enough to demineralise enamel, e.g. Veillonella dispar. They may be found within the plaque involved in the initiation of dental caries, but are likely to be secondary colonizers rather than primary pathogens.