Assessment of the polymerization contraction stress of composites photoactivated by halogen light and light-emitting diode.

Aim: The aim of this study was to compare the polymerization contraction stress of composites photoactivated by two light sources: quartz tungsten halogen light (QTH) and light emitting diode (LED).

Methods: Glass rods were fabricated (5.0 mm X 5.0 cm) and one of the surfaces was air abraded with aluminum oxide. An adhesive was applied to this surface and photoactivated by LED. The glass rods were assembled to a Universal Testing machine (Instron - 5565) and the composite were applied to the lower rod using a manual instrument. The upper rod was placed closer, at 2 mm, and an extensometer was attached to the rods. The twenty composites were polymerized by either by QTH (N.=10) or LED (N.=10). Polymerization was carried out using two apparatuses positioned in opposite sides, which were simultaneously activated for 30 seconds. Contraction stress was analyzed twice: shortly after polymerization (t30s) and 30 minutes later (t30min).

Results: The contraction stress for all composites was higher at t30min than at t30s, regardless of the activation source. Z100 showed lower contraction stress values (P<0.05) compared to the other composites. Regarding to Charisma and TPH, the photoactivation source had no influence on contraction stress, except for Z100 at t30min.

Conclusions: It was concluded that composite composition is the factor that most influence the polymerization contraction stress.