Effectivness of Composite Polymerization with LEDs of Second Generation

Introduction: The aim of this study was to compare a degree of conversion (DC) during polymerization of composite resins with two LED light curing units (LCU) of second generation. Methods: For measuring the DC, five samples were prepared for Tetric Ceram (TC)(Vivadent, Schaan, Liechtenstein) and Filtek P60 (P60)(ESPE, Seefeld, Germany) each. Unpolymerized composite sample was placed between two Mylar foils and pressed at 107 Pa to 0.1 mm thickness. For surface DC measurements, light source Bluephase (600 mW/cm2 first 5th sec, 1100 mW/cm2 to the end of illumination) and Bluephase C5 (500 mW/cm2) (both LCU from Vivadent, Schaan, Liechtenstein) were placed on the upper foil of the unpolymerized sample and polymerized (20 sec for TC and P60 with Bluephase, and 40 sec for TC and 20 sec for P60 with Bluephase C5). For measurements at 2 mm depth, overlayers 2 mm thick were made for each material. Light source was placed on the overlayer and polymerized in the same way as when measuring surface conversion. For determining DC, FTIR spectra of polymerized (P) and unpolymerized (U) samples were recorded using Perkin-Elmer spectrometer (Beaconsfield, Bucks, UK) and calculated according to Rueggebergs formula: % DC = (1-P/U) x 100% Results: The highest DC was reached in case of polymerization with Bluephase for both materials tested on the surface and 2 mm depth. There is no significant differenct between polymerization on the surface and 2 mm depth in case of illumination with both LCU, but there is signifficant difference between two tested materials in case of polymerization with both LCU. Conclusion: LCU with grater light intensity will enhance better polymerization but the difference in DC between composite materials may be influenced with different concentration of photoinitiators and co-initiators which spectrum lies outside the spectrum emitted from LCU tested.