(Blacksburg, Va., Nov. 22, 1998) -- Virginia Tech graduate student Nazan Gunduz and her fellow researchers in chemistry have developed improved dental materials that require one less step to process, to get you out of the dentist's chair faster. Your fillings will last longer, too.
A process called photopolymerization uses light as an activator to turn a liquid coating into a plastic to create insulating layers in electronic components or protective coatings on metal cans, for example. It is also used to harden dental filling material. Gunduz used PhotoDSC technology (a combination of light activation and differential scanning calorimetry) to measure the attributes of new materials developed by the Virginia Tech group.
At the American Chemical Society Biennial Polymer Symposium Nov. 22-25 in Williamsburg, Va., Virginia Tech adjunct professor Allan Shultz will present a poster on "PhotoDSC Polymerization of New Dimethacrylate Monomers," based on Gunduz's master's thesis research.
"Dentists use a thick paste mixture of two monomer liquids plus an inorganic filler such as fine sand or silica to produce white fillings for repairing front teeth," Shultz explains. "One of the monomers is a thick, viscous liquid and the other is a thin liquid. The addition of the thin liquid monomer is necessary to give the paste the proper consistency for the dentist to handle The mixture also contains a photoinitiator that, upon exposure to blue light, causes the monomers to join into a hard polymer network. This light-induced joining of the monomers into a network is photopolymerization."
"Chemists in our group at Virginia Tech have synthesized four new monomers, or dimethacrylates, that have low viscosities," Shultz says. "It will be possible to form a dental paste using only one of these new dimethacrylates rather than the mixture presently used. Also, due to the structures of the new dimethacrylates, the resulting tooth fillings will not absorb as much water as present fillings. Their good mechanical properties will therefore not be decreased as much as those of present fillings and the fillings should last longer," Shultz reports.
"Ms Gunduz, in collaboration with other members in our research group, has studied the photopolymerization kinetics of the four new dimethacrylate monomers and of the viscous monomer used in present dental resins," Shultz says. "A close approximation to present dental practice was followed by using a camphor quinone/amine photoinitiator system and blue light activation. The instrumentation employed was a commercial double beam light accessory (Perkin-Elmer DPA 7) attached to a DSC apparatus (Perkin-Elmer DSC 7)." He described the process: "The blue light illuminated both a reaction cell and a reference cell; the differential power input required to maintain the same temperature in the two cells is equal to the heat generation rate of the reacting material. The heat generation rate is proportional to the reaction rate," Shultz says. "Nazan could therefore calculate the reaction rate at any chosen time and the total amount of reaction that occurred in a given time period. Variation of photoiniator amount, light intensity and temperature produced a great amount of data of both scientific and practical value. Analyses of the rates of monomer conversion and the ultimate conversion of the monomers to hardened network products allowed comparison of the kinetics, efficiencies, and activation energies of the different monomers."
The new monomers were found to be superior in all aspects, Shultz reports. The Virginia Tech research group includes post doctoral fellows M. Sankarapandian and H.K. Shobha -- who are husband and wife, Gunduz, Shultz, and James McGrath, director of the NSF Science and Technology Center for High Performance Polymeric Adhesives and Composites. The work is supported by the NSF center and Virginia Tech's chemistry department.
Shultz, who has worked pro bono with the Virginia Tech chemistry department since his retirement from General Electric Corporate R&D in 1991, is one of the developers of the PhotoDSC process and technology. GE scientists J.E. Moore, S.H. Schroeter, and Shultz introduced the PhotoDSC technique in 1975 to study multifunctional acrylate and methacrylate photopolymerizations. In the same year that the initial PhotoDSC results were reported, Shultz made detailed drawings for the first sophisticated PhotoDSC apparatus -- built in the GE lab's machine shop -- to monitor the rate at which heat is released from a light-initiated reaction. Now several commercial companies produce such devices, but it was more than 10 years after the GE work that a commercial instrument appeared in the market place. A leading polymer scientist, Shultz has published and lectured worldwide.
Dr. Shultz can be reached at ashultz@vt.edu or at 540-231-7222.