Acidity and dental caries

By Sok-Ja Janket, DDS, MSEditor’s note: In recent research published in the British Dental Journal, scientists concluded that polyol-based sugar-free products may decrease the incidence of dental caries, but they may bring about another dental health risk — dental erosion — if the products contain acidic flavoring. Properly conducted clinical studies are needed in this area. Xylitol, as well as many other sugar alcohols, has been termed as nonfermentable sugars in the literature. However, some of these nonfermentable sugar alcohols can be metabolized by S. mutans and other strains of oral microorganisms. Many studies have shown that some bacteria are capable of fermenting sugar alcohols to some degree, which will lead to acid production and ultimately tooth decay, but in a lesser degree than table sugar.^1,2There are three notable properties of xylitol that have made it an important sugar alcohol in dental research:

1. Most importantly, xylitol is not readily fermented by oral bacteria, especially the species of Streptococci mutans.
2. It has also been shown to reduce the amount of S. mutans in the oral cavity by limiting the source of fermentable substrates for these bacteria to survive.
3. Xylitol can induce the production of salivary enzymes, which lead to the inhibition in growth of bacteria in plaque.

Together, these traits are important in reducing the amount of dental caries seen in patients. The caries-prevention ability of xylitol has been well established. However, when acid is added for flavor and as preservatives, the acid actually cancels out the benefits of caries prevention by xylitol. This is the topic and main theme of our review. Dental professionals can recommend nonacidic xylitol products that are safe and low-cariogenic. There are nonacidic sugar-free confections in flavors of peppermint, spearmint, wintergreen, mint chocolate chip, or butterscotch. Clinicians should also educate their patients to read ingredient listings and avoid products containing acids, such as ascorbic, adipic, glutaric, succinic, fumaric, mallic, or tartaric acids. Regardless of the acid type, such acids will cause patients’ salivary pH to fall well below the critical level where erosion can occur.Acidity and dental cariesAlthough research on salivary pH and demineralization of enamel was active even in the 1950s,^1,3 the most important work was conducted by Kleber and colleagues in late 1970s.⁴ They found that when the pH of the saliva is below a critical value of 5.5, tooth enamel demineralized. If the saliva is above the critical pH of 5.5, it is considered supersaturated and favors crystallization of the mineral.⁵ When the pH of saliva falls below 5.5, it is considered unsaturated, and thus provides a favorable condition for the mineral to dissolve.⁵ Under normal conditions, teeth do not lose mineral because the saliva is usually supersaturated in relation to mineral concentration.⁵The presence of calcium and phosphate in the saliva may change the dynamics of demineralization of tooth enamel in relation to pH.⁵ Although the focus of their study was sugared candies, Wagoner and colleagues compiled the pH changes in sour candies.⁶