Plaque-resisting dental material kills microbes

US team develops robust material for dental filings that kills decay-causing microbes and resists formation of plaque

Dental materials used to repair cavities can themselves cause problems. The sticky film of bacteria known as plaque can build up just as easily on their surface as it can on tooth enamel; and once there, the bacteria produce acid that can attack the enamel adjacent to the filling. Researchers at the University of Pennsylvania have now developed a dental material that, they claim, will not have this problem.

Plaque formation on a control surface, left; the imidazolium-containing material on the right has hardly any bacteria

Previous attempts at making plaque-resistant dental materials have focused on incorporating a drug active ingredient into the material, but this can have unwanted side-effects, the team said.

The amount of drug in the material needs to be quite high, and this can damage cells in the gum; moreover, incorporating these compounds into the material can weaken its structure, rendering it ineffective as a repair agent.

“Dental biomaterials such as these need to achieve two goals,” said Geelsu Hwang, a researcher at Penn’s medical school who collaborated on the project. “First, they should kill pathogenic microbes effectively, and, second, they need to withstand severe mechanical stress, as happens when we bite and chew.”

Hwang, who has an engineering background, helped the team to take a different approach. Rather than using a drug, they used an antibacterial agent, imidazolium, that can be tethered into the structure of the material and prevented from leaching out. Imidazolium kills on contact, so it is still effective when fixed into the matrix. The material is described in the ACS journal Applied Materials and Interfaces.

The material used imidazolium attached to a polymerisable resin through a carbonate linking group, incorporated into a methacrylate (acrylic) scaffold composite. In tests, this killed cells of the bacterium Streptococcus mutans, which cause plaque, on contact, and prevented the bacteria from forming a sticky biofilm. Only negligible amounts of bactetria were able to adhere to the material compared with a control material, and any accumulation could be washed away easily.

“The force equivalent to taking a drink of water could easily remove the biofilm from this material,” Hwang said. The non-leaching nature of the antibacterial agents also reduces the likelihood of the bacteria developing resistance, he added.