Polymer-based Materials Change the Face of Dentistry

Doctoral students Lale Lovell and Hui Lu are helping to develop more durable polymer-based dental materials.

The last time you had a cavity filled, it's likely that your dentist used a high technology device that looked a lot like a laser and emitted very intense blue light. In fact, the dentist was performing a photopolymerization to cure your restoration in place.

Over the last 30 years, polymer-based restorative materials have become the dominant choice for dental restorations, replacing more traditional gold and amalgam fillings as patients demand more "tooth-like" appearance and performance.

Supported by grants from the National Institutes of Health and the new Industry/ University Cooperative Research Center for Fundamentals and Applications of Photopolymerizations, researchers in the Department of Chemical Engineering and the University of Colorado's School of Dentistry are working to develop the next class of polymeric dental restorative materials. These materials will cure more rapidly and yield improved restorations with greater durability.

Polymer-based dental materials initially consist of two distinct parts: a monomer mixture and dispersed glass or ceramic particles. The filler materials are present to improve the mechanical and wear properties of the restored cavity, and the polymer matrix, after curing, acts as the structural support of the composite material. After the restorative material is placed into the prepared cavity, the monomer is polymerized in situ by the application of the intense blue light.

Current polymer restorative materials have several drawbacks that are the target of the on-going research. These problems include relatively slow reaction and long curing times, the presence of unreacted monomer molecules that are potentially extractable into the body, reduced mechanical properties compared to amalgam, swelling caused by water uptake of the restoration, and volume shrinkage that takes place during the polymerization, often leading to micro-cracking at the interface of the restoration and the tooth.

For the last five years, Professor Christopher Bowman's laboratory has performed detailed studies to understand the current polymer system and to use that to improve its performance. One focus of the work has been on increasing the conversion of reactive double bonds present in the monomer from the current attainment of 60 percent, thereby reducing the amount of unreacted monomer that might be extracted into a patient's body. The research group has developed models for how the double bond conversion evolves with time, and used these to increase the final double bond conversion by as much as 20 percent.

In collaboration with Professors Jeffrey Stansbury and Sheldon Newman at the Health Sciences Center, Dr. Bowman's group also has worked to develop monomer systems that polymerize more rapidly. In one exciting recent development, this team has synthesized a monomer system that reacts more than twice as fast as the current resin system, shaving minutes off a total dental procedure. Though further improvements are still needed, it is hoped that the enhanced polymerization speed will lead to cheaper, more durable fillings.

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