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VRC scientists working on new class of dental resin composites

August 24, 2015

By Jean Williams

Dr. Sun
Gaithersburg, Md.— If ADA Foundation Dr. Anthony Volpe Research Center project leader Jirun Sun, Ph.D., has anything to do with it, someday dentists will fill their patients' caries with a new, improved generation of dental resin composites.

Dr. Sun received a Ph.D. in polymer physics from Louisiana State University. His research at LSU focused on the preparation and characterization of nanoparticles, fibers and hydrogels using multiple methods, including small angle X-ray scattering and light scattering. Immediately after completing his Ph.D. in 2006, he was invited to study dental composites materials at the National Institute of Standards and Technology.

Dr. Sun came directly to the VRC in March 2009 after his post-doctoral studies at NIST. His primary focus at VRC is the development of dental restorative materials, including dental composites, and is principal investigator on a project called Novel Dental Resin Composites with Improved Service Life. In 2013, the National Institutes of Health/National Institute of Dental and Craniofacial Research awarded the VRC a five-year grant to support this project.

"For dental composites, there are three major parts," Dr. Sun said. "Resin networks, fillers, and coupling agents which connect the fillers and the resin networks. My projects focus on these three components."

Through his current composite project, Dr. Sun seeks to solve challenges about longevity for current dental resin composites. "The current dental resins were invented by Dr. Rafael Bowen in 1962, and have served well in treating cavities for decades," Dr. Sun said. "They are good, but they have limitations. The average service life of the composite made out of these resins is less than eight years. We want to increase the service length of composites by replacing the current resins with our new resins. Traditional composites contain ester groups, which can decompose or be degraded over time by water or by enzymes in saliva. With our new resins, we're using ether groups that won't degrade under the above challenges. We have already proved this in our new compounds. Enzymes don't appear to degrade our new resins. We want the new restorative materials to last a lifetime."

Dr. Sun sees promising results already. "It's in the early stage, but our concept is proven," he said. "With the current dental resins, we observed significant weight loss and mechanical performance reduction after only 16 days under enzymatic challenges. In contrast, our new resins showed no change."

For the fillers, Dr. Sun invented a self-healing system that can repair microcracks. One challenge to filling longevity is the detection and restoration of microcracks and fractures in the material after placing it in patients' teeth. The microcracks that might cause failure for the fillings are very difficult to detect and almost impossible to be repaired manually. Dr. Sun has confirmed that the new filler system can heal the microcracks without any external intervention, potentially increasing service life. In addition, this self-healing system is made with clinically tested, biocompatible materials, which makes it readily applicable to medical devices. Dr. Sun is patenting this system for dental applications.

Dr. Sun and his team, including postdoctoral research associates Drs. Yin Yang, George Huyang and Sheng Song, are also making a smart defense system utilizing the coupling agents to sense the environment change and release antimicrobial drugs when needed. This system applied advanced chemistry and nanotechnology into dental resin composites to achieve strength and targeted drug delivery simultaneously.

When all is said and done, Dr. Sun and his team might produce a dental composite that he said is a "dream come true": strong, durable, nontoxic, self-healing, and able to release antimicrobial drugs when needed.

One of the highlights for Dr. Sun of working at VRC is getting to collaborate with prestigious scientists including Dr. Laurence Chow and Dr. Rafael Bowen. Dr. Bowen, who headed VRC (then known as the Paffenbarger Research Center) from 1983-1994, patented the Bis-GMA/TEGDMA dental resin composite restorative system in 1962. Drs. Bowen and Sun applied for a patent together on the new dental resins in 2014.

"Dr. Bowen is an enthusiastic and productive researcher," Dr. Sun said. "To me, he's a working legend. It's really great for me to be able to team up with him."

Dr. Sun also appreciates working closely with his contemporary researchers at the VRC and his easy access to various experts on the NIST campus. "This is a very good environment for research. We can easily make contacts with scientific experts from various disciplines," he said. "Other researchers, like the project leaders right now, are pretty young. We're all working hard and we collaborate a lot, helping each other. That's a very friendly environment to work in. There are many opportunities and we are enjoying the work that we are doing."

The VRC is on the grounds at NIST, a federal government research campus, where it has been since 1928. Previously operated by the ADA and now by the ADA Foundation, the lab conducts unique research in cutting-edge fields of biomaterial and tissue engineering technologies.