I read with great interest the article "Curing Restorative Resin: A Significant Controversy" by Dr. Gordon J. Christensen in July JADA. I found the article to be insightful and interesting, but have to respectfully disagree with an important point made by Dr. Christensen. He said, "Both scientific and empirical evidence support the use of fast-curing lights."
Using Fourier Transform Infrared Spectroscopy in our own laboratories, we have shown that polymerizing composites using one kind of plasma arc light inadequately polymerized composite resins (
Latta MA, Stanislav CM, Barkmeier WW. Polymerization conversion of composite resins using different curing devices [abstract 1519]. J Dent Res 2000;79[special issue]:333
).
In this laboratory investigation, the plasma arc light used for six seconds of total polymerization time (double the manufacturer’s recommendation) polymerized a 2-millimeter thickness of a hybrid composite to less than 75 percent of the level generated with a standard halogen light and a packable resin to less than 50 percent of a 2-mm thickness.
I cannot say with certainty what the clinical effects of underpolymerizing these composites would be. I believe, however, that underpolymerization can lead to mechanical failure (fracture) or increased wear because of the lack of double bond conversion in the resin.
In the absence of evidence-based clinical data, I believe the use of these lights at very short cure times should be done with great caution. I can think of no dental manufacturer who would expect maximum performance from their restorative material if that material were significantly underpolymerized.
Interaction of a light-cured composite with a curing device is dependent on many factors, including the shade of the composite and the specific chemical composition of the resin. The clinical performance of these materials can be significantly affected by the size, the types and the location of the restoration in the dental arch. This could certainly account for the apparent empirical clinical success in the short term of resins polymerized with fast curing.
However, in the absence of long-term, well-controlled clinical data, I must emphasize again that the laboratory evidence would suggest caution in polymerizing composites with fast-curing lights, particularly, in my view, when these resins are placed in stress-bearing areas.
The opinions expressed herein are the personal views of the author and do not necessarily represent those of Creighton University.
