"Two for one" is a great marketing strategy — for certain things. Two bags of chips for the price of one? Yep. Two nights hotel stay for the price of one? Yes, please.

But an additional cavity (called recurrent caries) beneath the filling of a cavity that was already filled? Uh, no thanks. Unfortunately, many dentists have to deliver this bad news to patients on a daily basis.

Bacteria can dig under tooth-colored fillings and cause new cavities. These recurrent caries happen to about 100 million patients every year and cost up to an additional $34 billion to treat.

But a recent research collaboration between the University of Toronto's Faculty of Dentistry, Department of Materials Science & Engineering and the Institute of Biomaterials and Biomedical Engineering has shed some good news on this negative phenomenon.

In the study that was published in the journal Scientific Reports, three dental research colleagues proposed a creative solution to pesky recurrent caries. Professor Ben Hatton, Professor Yoav Finer and Ph.D. student Cameron Stewart discovered that a cavity filling material packed full of tiny particles, which includes a specific amount of antimicrobial drugs, could stop bacteria in its tracks.

These microscopic particles are small but mighty. And they may just solve one of the most significant challenges with antibacterial filling materials: how to store enough medication within the material to be effective at warding off bacterial decay for a person's entire life.

Adding these particles brimming with antimicrobial drugs to a filling material creates an effective line of defense against cavity-causing bacteria. "But," said Hatton, "traditionally there has only been enough drug to last a few weeks."

Through this study, researchers found that a combination of medication and silica glass actually self-organized in a specific molecule-by-molecule way on a microscopic level and maximized the drug's density, providing enough supply to last for years.

This discovery means that as much as 50 times the amount of bacteria-fighting drugs can be packed into the molecules of this new "smart" material. Since dentists know that bacteria specifically attack the margins between fillings and the remaining tooth structure, using this new material can ward off the problem of recurring cavities for years.

More testing needs to take place to determine how this new material will fare in the complex, saliva-filled environment of the mouth. These tests are already underway. But with some careful testing and fine-tuning, this new smart material could ultimately create a stronger filling.