Stopping Tooth Decay Without Killing Beneficial Bacteria

Recent scientists have reported a treatment that could stop plaque and cavities from forming using a new type of cerium nanoparticle formulation that in the future would be applied to the teeth at the dentist’s office. 

The mouth contains over 700 species of bacteria which includes beneficial strains that help to digest food or keep other microbes in check, but this also includes harmful strains such as streptococcal species including Streptococcus mutans which will begin to stick to the teeth and multiple shortly after cleaning. Using sugar as an energy source and building block these harmful microbes will gradually form a tough film that is not easy to remove by just brushing. As they continue to metabolize sugar they also make acid byproducts that can dissolve tooth enamel, leaving your teeth more prone to developing cavities. 

You can fight back with products including stannous fluoride to inhibit plaque, and silver nitrate or silver diamine fluoride to help stop existing tooth decay. Nanoparticles made from zinc oxide have also been studied but repeated applications can lead to stained teeth and bacterial resistance, according to principal investigator Russell Pesavento, D.D.S., Ph.D., of the University of Illinois, Chicago. "Also, these agents are not selective, so they kill many types of bacteria in your mouth, even good ones," he explains.

Looking to find an alternative that would not kill beneficial mouth bacteria the researchers investigated cerium oxide nanoparticles on mouth microbes. The team produced their nanoparticles by dissolving ceric ammonium nitrate or sulfate salts in water. Polystyrene plates were seeded with S.mutans in growth media and when the bacteria were fed sugar in the presence of the cerium oxide nanoparticle solution they formulation was found to reduce the biofilm growth by 40% compared to plates without the nanoparticles. However, it was noted that the team was not able to dislodge existing biofilms, and silver nitrate showed no effect on biofilm growth under similar conditions. 

"The advantage of our treatment is that it looks to be less harmful to oral bacteria, in many cases not killing them," Pesavento says. Instead, the nanoparticles merely prevented microbes from sticking to polystyrene surfaces and forming adherent biofilms. In addition, the nanoparticles' toxicity and metabolic effects in human oral cells in petri dishes were less than those of silver nitrate.

Pesavento was awarded a patent in July 2020 but would like to continue advancing his formulation so that dentists would be able to paint it onto a patient’s teeth. Before that can happen the team notes that there is still a lot of work to be done. Currently, the team is working on developing coatings to help stabilize the nanoparticle at a neutral or slightly basic pH closer to the pH of saliva and healthier teeth than the present solution. The team is also investigating bacteria linked to the development of gingivitis to limit adherent biofilms. 

Abstract:

“Streptococcus mutans has long been a target of interest for antimicrobial therapy in the field of oral medicine. S. mutans produces robust tooth-borne biofilms that serve a key etiological factor in the progression of dental caries and odontogenic infections. Silver-based bactericidal agents have proved effective at reducing oral S. mutans proliferation, yet their repeated administration has raised concerns of emerging bacterial resistance and deleterious effects on oral microbiota. Tooth-applied biofilm inhibitors with non-lethal mechanisms of action have offered a novel approach for both limiting biofilm formation and reducing effects on the entirety of the oral microbiome. The use of nanoparticles in this capacity has received considerable interest in recent years. Although several studies have focused on the antimicrobial effects of cerium oxide nanoparticles (nanoceria, CeO2-NP) few have focused on their effects on clinically relevant bacteria under the initial biofilm formation conditions. In this work, nanoceria derived solely from Ce(IV) salt (i.e., ceric ammonium nitrate, CAN; ceric ammonium sulfate CAS) hydrolysis were found to reduce adherent in vitro S. mutans growth in the presence of sucrose by approximately 40% while commercial dispersions of "bare" nanoceria (3 nm, 10-20 nm, 30 nm), Ce(NO3)3 (CN) or ammonium salts (AN, AS) alone were either inactive or observed to slightly increase biofilm formation under similar in vitro conditions. Planktonic growth and dispersal assays support a non-bactericidal mode of biofilm inhibition active in the initial phases of biofilm production. Human cell proliferation assays suggest only minor effects of hydrolyzed Ce(IV) salts on cellular metabolism at concentrations up to 1 mM Ce, with less observed toxicity compared to equimolar concentrations of AgNO3 - a long used intraoral antimicrobial agent. The results presented herein have potential applications in the field of oral medicine.”