Traditional silver fillings have largely given way to plastic-based composite resins that match the color of teeth. These resins, however, tend to shrink, which leads to tiny gaps between the tooth and the filling, allowing bacteria to creep back in to the tooth and cause more decay. They also are weaker than amalgam fillings and tend to wear away and discolor after several years, so they need to be replaced. Enter new shrinkage-resistant materials, currently being tested and developed by an interdisciplinary group of scientists from the Health Science Center and Southwest Research Institute. The component closest to being realized is based on liquid crystal monomers, and is being developed by a team headed by Barry K. Norling, Ph.D., associate professor of restorative dentistry.
Monomers are molecules that can be chemically linked together to form a polymer.
But the hardening is accompanied by shrinkage. The new resins reduce shrinkage from the current 8 percent to 2 percent. Dry spaghetti, on the other hand, is aligned and packs together tightly. What we're doing with these materials is making them more like dry spaghetti. Dr. Norling explained that the aligned molecules become unaligned during curing to a solid polymer, losing the initial tight packing and yielding a kind of virtual expansion that compensates for much of the shrinkage that inevitably occurs when monomers are converted to polymers.