You might think that with today's composite dental fillings, once you get a tooth filled, it's good for life. According to the University of Oregon's Prof. Jamie Kruzic, however, "almost all fillings will eventually fail" – some within as little as six years. That's why he's part of a team that's looking into a longer-lasting filling material: bioactive glass.

Currently, composite fillings are made from a blend of polymers and inert glass fillers. As its name implies, though, bioactive glass is not inert. Composed of compounds such as phosphorus oxide, silicon oxide and calcium oxide, it repels oral bacteria that cause tooth decay. More specifically, it is thought that ions released from its calcium and phosphate content have a toxic effect on the bacteria.

One of the main reasons for the breakdown of fillings is what's known as secondary tooth decay. This occurs when bacteria colonize the interface between the filling and the tooth, causing the tooth to essentially decay from the inside out. In lab tests on recently-extracted human molars, however, teeth with fillings containing the bioactive glass where considerably more resistant to secondary tooth decay.

The glass itself comes in the form of a powder, which is blended with polymers like those already used in regular fillings. Once set, the composite is very hard – in fact, when composites which were 15 percent bioactive glass by weight were analyzed, they were found to have mechanical properties that were similar or even superior to those of conventional dental composites.

Kruzic says that if clinical trials back up the results they've seen in the lab, it should be very easy to incorporate bioactive glass into existing formulations for composite tooth fillings.

A paper on the research – which also involved scientists from the School of Dentistry at the Oregon Health & Science University and the College of Dental Medicine at Midwestern University – was recently published in the journal Dental Materials.