Effect of Pulse-Delay Curing on Resin Composite Hardness

Methods: A halogen curing light (Optilux 501, Kerr) was used to polymerize six resin composites (Vit-l-escence A2, Filtek Supreme A2B & A2D, Tetric Ceram Bleach XL, HeliomolarHB A2 and Aelite PLS A2). The composites were packed into molds 2 mm deep with an inside diameter of 6 mm. A thin Mylar strip placed on the top and bottom surfaces. The composites were cured using either 40 seconds of continuous light irradiation, or using a pulse-delay protocol of 5 seconds followed by an additional 35 seconds (total of 40 seconds) five minutes later. The specimens were stored in a light proof container in air for one hour before measuring their Knoop microhardness. Three readings were taken at the center of the top and bottom surfaces of the composites. A total of three trials were completed in random order for each resin composite.

Results: Repeated measures analysis of variance followed by pairwise t-tests showed that the 40 seconds of continuous light irradiation always produced the hardest composites (p<0.001) at both the top and the bottom of the specimens, although the magnitude of the difference between the continuous curing vs. the pulse-delay was not the same for all composites. This may explain why the post-gel polymerization stress is reduced when the pulse-delay technique is used.

Conclusions: Even though the composites received the same total energy, in all cases the pulse-delay technique produced softer composites.