Lactic acid or lactate is produced by cariogenic bacteria within dental plaque attached to the surface of a tooth. The cariogenic bacteria break down sucrose to glucose and fructose. Glucose and fructose are then broken down to produce energy (ATP) for the cariogenic bacteia. A byproduct of this fermentation pathway is lactic acid. The lactic acid is secreted from the cariogenic bacterial cells into the dental plaque. Lactate lowers the pH in the dental plaque and over the surface of the tooth that the dental plaque is attached to. When the pH gets to 5.5 or lower the surface of the tooth under the dental plaque will demineralize. If demineralization times are long when compared to remineralization times a cavity will form.
Lactobacillus sp. got the first part of their name (i.e., Lacto-) because they get energy (ATP) from sugars like lactose (disaccharide made up of glucose and galactose) and sucrose (disaccharide made up of glucose and fructose) via glycolysis and the lactic acid fermentation pathway. Streptococcus sp. also break down sugars to energy (ATP) and lactate using glycolysis and the lactic acid fermentation pathway.