Bacteria living in dental plaque contribute to tooth decay which is often resistant to traditional antimicrobial treatment. Researchers at the University of Pennsylvania took advantage of pH sensitive and enzyme like properties of iron containing nanoparticles to catalyze the activity of hydrogen peroxide. The activated hydrogen peroxide produced free radicals that were able to degrade the biofilm matrix associated with tooth decay and kill bacteria thus preventing plaque and reducing tooth decay.
The researchers said that even a low concentration of hydrogen peroxide was effective at disrupting the biofilm. It was found that adding nanoparticles increased the efficiency of bacterial killing more than 5,000-fold. The work built off a seminal finding published in 2007 showing that nanoparticles, long believed to be biologically and chemically inert, could in fact possess enzyme-like properties. This study showed that an iron oxide nanoparticle behaved similarly to a peroxidase, an enzyme found naturally that catalyzes oxidative reactions, often using hydrogen peroxide.
Some of the researchers were skeptical to use nanoparticles in an oral setting to kill bacteria because the free radicals can also damage healthy tissue. However the nanoparticles’ activity is dependent on pH and had no catalytic activity at neutral or near-neutral pH of 6.5 or 7, which are values typically found in a healthy mouth. But when pH is acidic, such as near 5, they become highly active produce free radicals.
The researchers first used in vitro studies, which involved growing a biofilm containing the cavity-causing bacteria Streptococcus mutans on a tooth-enamel-like surface and then exposing it to sugar. When this was done it was confirmed that the nanoparticles adhered to the biofilm and could effectively catalyze hydrogen peroxide in acidic conditions. They also showed that the nanoparticles’ reaction with a 1% or less hydrogen peroxide solution was effective at killing bacteria, wiping out more than 99.9% of the S. mutans in the biofilm within five minutes.
The researchers next used an animal model were they applied the nanoparticles and hydrogen peroxide topically to the teeth of rats, which can develop tooth decay when infected with S. mutans. Twice a day, 1 minute treatments for 3 weeks was found to significantly reduce the onset and severity of carious lesions when compared to the control or treatment with hydrogen peroxide alone.
An additional advantage is that the platform with nanoparticles uses a concentration of hydrogen peroxide, 1%, which is lower than many currently available tooth whitening systems that use 3% to 10% concentrations of hydrogen peroxide, which can help reduce potential side effects. It will be interesting to see this research progress as the nanoparticle size, coatings, and composition are refined for the best effectiveness.
Lizeng Gao and et al. Nanocatalysts promote Streptococcus mutans biofilm matrix degradation and enhance bacterial killing to suppress dental caries in vivo. Biomaterials, 2016; 101: 272