Polymerization and Mechanical Properties of Contemporary Composites: LED OR QTH?

Objectives: The aim of this study was to compare the depth of cure (DOC), Vickers hardness (VH), flexural strength (FS) and elastic modulus (E) of bulk-fill, low-stress and conventional composites cured with LED or QTH light-curing units.
Methods: Four high-viscosity bulk-fill composites; Sonic-Fill (SF), Tetric N Ceram Bulk Fill (TBF), Filtek Bulk Fill (FB), everX Posterior (eXP), two low-viscosity bulk-fill composites; Venus Bulk Fill (VB), Surefil SDR (SDR) and two low-stress composites; Kalore (K), Charisma Diamond (CD) and one conventional composite Filtek Z250 (Z250) were tested. All the specimens were prepared according to ISO 4049 for the tested parameters (n:20 from each composite for F-E and HV; n:10 for DOC), polymerized according to the manufacturer’s instructions with LED (Demi Ultra) or QTH (Optilux 501) and stored in distilled water at 37 °C for 24 h before the measurements. HV was evaluated on the top, at 2mm and 4mm of each specimen (Buehler) while DOC was calculated as the 80 % hardness drop-off by using a HV profile, starting from the surface. FS and E were determined by three point bending test (Instron). Data were analyzed by two-way ANOVA and post hoc Tukey’s tests (p<0.05).
Results: The tested composites cured with LED showed statistically significant higher mechanical properties than cured with QTH (p<0.05). ExP presented the highest FS and E while VB presented the lowest than all the other composites (p<0.05). SF showed significantly the highest HV either in top, at 2mm and 4mm, while VB recorded the lowest for both LED and QTH. DOC of all the tested bulk-fill materials exceeded 4mm with LED and QTH.
Conclusions: LED curing was found to be more successful than QTH with respect to the tested polymerization and mechanical properties. Mechanical properties of high-viscosity bulk-fill composites cured with LED or QTH were similar to or better than those of low-stress and conventional composites.