June 20, 2005
Most dentists today use commercial dental composites that still utilize Bowen’s original, now 40-year-old Bis-GMA monomer as the matrix-forming resin. Thus, despite steady progress over the past several years in learning how best to fill and cure these composites in decayed teeth, dentists still run into the same basic laws of chemistry that Bowen confronted. That is, because the curing process involves free-radical initiation for monomer polymerization, a bonded posterior composite will lose some volume, shrink, and over time stress the patient’s tooth. In the June 10 issue of the journal Science, NIDCR grantees and colleagues demonstrated a cross-linked polymer mixture that, when exposed to light during the curing process, reversibly cleaves its chemical backbone to allow monomer chain rearrangement for rapid stress relief. Remarkably, the polymer does so without any degradation of its mechanical properties. The polymer mixture consists of pentaerythritol tetra (PETMP) and triethyleneglycol divinylether (TEGDVE), which produced a rubbery network with a glass transition temperature of about -25 degrees Celsius. The authors noted, “Although our study involved model rubbery networks, this process may also be applied to a vast array of other applications for which the control or elimination of stress is critical.”