Researchers at Tokyo Medical and Dental University have conducted a laboratory work to fabricate an oral stent for prevention and treatment of dental caries. The oral appliance (stent) was entirely made of ethylene-vinyl acetate copolymer reinforced with silver particles (5,000 ppm) to induce maximum antibacterial effect against a wide range of species that are involved in the decay pathogenesis, namely, S. sobrinus, P. gingivalis, and E. coli. Silver nanoparticles have strong antibacterial properties as they disrupt their proteins and enzymes’ synthesis in order to prevent biofilm formation. However, there is a huge global effort to verify the safety of silver nanoparticles and to understand their mechanism of action against bacteria in variable concentration(s).

This teamwork prepared a batch of silver-reinforced ethylene-vinyl acetate copolymer in the form of paste which was then molded into sheets. The fact is that embedding silver nanoparticles inside a paste is believed to initiate stronger antibacterial effect than the coating method and over a longer period of time. The oral stent was shaped as a sports’ guard, consisting of 2 layers, where silver nanoparticles were dispersed in the inner layer which is the fitting surface toward teeth. The lab fabrication process involved heating the 3-mm sheets followed by vacuum forming; then, special surface treatment with organic dissolvent was done to partially expose the silver particles. It was also possible to include derivatives of glass ionomer into the composition of the appliance for further anti-cariogenic effect.

It was also important to consider an appropriate storage method, as such appliances can be used for months. Washing the appliance to remove stains and keeping it in a dry atmosphere without dirt or dust contamination was the most useful way to avoid bacterial growth.

As a sports’ guard, the material had to exhibit some shock-absorption criteria to disperse energy around all surface area of the stent, while being durable enough to resist fracture. The measurements of the antimicrobial action of such plastic surfaces was parallel with the modified guidelines of ISO 22196 standards. This guard showed nearly 37.5% more load absorbency than other commercially available guards (1.75 folds).