Whether you call them bottles of pop or bottles of soda, regularly guzzling soft drinks can lead to tooth decay. Over time, the acidic beverages erode hydroxyapatite (HA), a major component of tooth enamel.
For those unwilling to give up the sugary drinks, help may be on the way: Researchers in Sweden have determined how potential soft drink additives could protect teeth.
In the past, food scientists and dentists have suggested adding food-safe, HA-preserving polyelectrolytes to beverages. But little was known about how these conductive polymers might provide protection. Javier Sortes of Malmö University and coworkers have now employed surface imaging techniques to better understand how the potential additives interact with saliva coatings on the surface of teeth (ACS Appl. Mater. Interfaces 2015, DOI: 10.1021/acsami.5b07118).
The researchers prepared a flat layer of HA and coated it with human saliva to simulate the protective layer, or pellicle, of proteins and other salivary molecules that accumulates on teeth. They then challenged the model tooth surface with three fluids at a pH of 3.2, near that of many soft drinks: One contained citric acid alone, and the others contained citric acid mixed with either an anionic polyelectrolyte, carboxymethyl cellulose, or a cationic polyelectrolyte, chitosan.
Ever since researchers realized that chitosan could prevent the acid erosion of hydroxyapatite, “I have been curious to find out how the interaction of polyelectrolytes and pellicle under erosive acidic conditions affects hydroxyapatite surfaces,” says University of Pennsylvania materials chemist Hyun-Su Lee, who was not involved with the study.
Using atomic force microscopy and other surface techniques, the team found that anionic carboxymethyl cellulose sinks past the top layer of the pellicle and mingles with small proteins near the HA. Cationic chitosan, in contrast, adsorbs on top of the pellicle, possibly by cross-linking with large glycosylated proteins called mucins in the outer layer. Sortes thinks these mechanisms are likely consistent across all anionic and cationic polyelectrolytes.
Chitosan better protected HA, the team found, but Sotres cautions that because the HA is flat in these models, the study does more to illuminate the polyelectrolytes’ protective mechanisms than to establish which substance offers the most protection on the more complex shapes of real teeth. But with this new mechanistic understanding, Sortes says beverage manufacturers have new clues to help protect their customers from tooth decay.