Effect of a LED versus halogen light cure polymerization on the curing characteristics of three composite resins

To evaluate the effect, in vitro, of a LED (GC E Light) versus an halogen (Astralis 7) polymerization on the mechanical properties of three commercially available microhybrid composite resins.

Three commercially available composite resins (Tetric Ceram, Charisma, and Z100), and six modes of polymerization were evaluated (one mode for Astralis (AST): HIP 40 seconds and five modes for the GC E Light (GCE): standard 40 seconds, fast cure 6 seconds, fast cure 12 seconds, soft cure A 39 seconds, and turbo 10 seconds) in terms of top surface and bottom surface (2 mm-depth) microhardness, and flexural strength. Five specimens of each composite resin were made for the two mechanical properties tested. Five hardness values were recorded on each side for each sample with a Vickers diamond indenter. A three point bending test was performed at a crosshead speed of 1 mm/minute. Statistical comparisons were made using a two-way ANOVA (composite resin, polymerization mode) and a Fisher's test (P < 0.05).

Z100 presented highest properties for both tests. Top surface microhardness: for Tetric Ceram and Charisma, the longer the exposure time, the higher the results, with no difference between AST mode and the longer GCE modes. For Z100, the highest values were obtained with AST. Whichever the material, short times (fast cure 6 seconds and turbo) exhibited poor results. Bottom surface microhardness: the samples cured with AST presented higher results but quite similar mechanical properties were achieved with the fast cure 12 GCE mode of the LED LCU. Fast cure 6 seconds and turbo obtained the lowest results. Flexural strength: the results were comparable with those obtained in bottom microhardness.