Research result could change tooth repair

Since late August, fourth-year physics student Nicole Nagy has been working alongside Assem Hedayat, an assistant professor of dental materials. The two started working together after one of Nagy's faculty mentors, Professor Julia Boughner from the Department of Anatomy and Cell Biology, put out a call for researchers interested in working with a promising physics student.

Hedayat was looking to examine whether the materials used in dental fillings are able to travel through tubules—microscopic channels located in a tooth's dentin—and reach the pulp. Such research could shed light on whether or not these tubules serve as portals that allow dental materials to enter the body. However, because these tubules have a diameter of only about two microns, Hedayat was hoping to enlist the help of a physicist to assist with a 3D imaging process.

When Nagy was approached by Hedayat about the opportunity, she was immediately intrigued.

"There were a lot of physics applications and techniques that were going to be used in the project so I thought it would be a great experience," explained Nagy.

To begin, Hedayat began contacting advanced-imaging facilities across North America and got a quick reply from the Lawrence Berkeley National Laboratory in California. A scientist in charge of the lab's beamline told Hedayat if he sent samples they could be tested quickly.

Members of Hedayat's research team prepared and applied fillings to previously untouched teeth from the College of Dentistry's tooth bank, and the samples were sent to the Berkeley synchrotron. While the images that Hedayat got back weren't refined enough to view the dentinal tubules, they did show something unexpected.

"When Nicole started analyzing data and the images, we were surprised to see some other objects under the fillings, which were shiny particles," explained Hedayat. "And that's where the whole project took a different turn."

Hedayat said those gleaming fragments, easy to see in the images, could only have come from the drill bits used to apply fillings to the teeth. The next step is to analyze the fragments themselves and determine their composition. Generally, dentistry drill bits are composed of tungsten carbide, although sometimes cobalt is added to bind the carbide particles together.

Tungsten carbide on its own is biocompatible, said Hedayat, but tungsten-carbide-cobalt is biohazardous. "You have to remember that if we're finding one or two fragments in these teeth, how many more splash around in someone's mouth and end up being swallowed? The fragments' edges are also very sharp, and can lodge themselves inside the oral cavity or body."

If it is determined that the particles pose a potential health hazard, Hedayat said it is possible that research into alternative dental tools could be accelerated.

"One of my colleagues pointed out that … maybe we need to look more at lasers in the industry," he said. "As researchers, that is something we may need to look into from a variety of perspectives. That's the beauty of collaboration— different ideas come up when we work together to stop things like this from happening."

While analyzing the fragments' composition will be the next step in this research, Hedayat said he and Nagy will also be revisiting their original objective and attempting to get higher-resolution images of the dentinal tubules. They hope the Canadian Light Source, or perhaps a micro-CT scanner, will be able to help in that regard.

Nagy said this experience has been invaluable, both in terms of the hands-on research she has been involved in and the project's interdisciplinary nature. While she is not yet sure what to pursue after graduating next spring, Nagy said medical physics and dentistry are both high on her list.

"This project is a really unique combination of sciences all working together. We're all seeing things from different points of view, and then to talk to people and hear how they're interpreting things, it's really interesting," she said.