title: Comparative study of surface microhardness of methacrylate-based composite resins polymerized with light-emitting diodes and halogen.
abstract: OBJECTIVE
  The aim of this study was to evaluate the effect of polymerization with quartz-tungsten-halogen (QTH) and light-emitting diodes (LED) on the surface microhardness of eight commercially available light-polymerized, methacrylate-based composite resins, with different filler particle composition (microfill, minifill, nanohybrids, and microhybrids) immediately after polymerization, after 24 hours, and after three months of storage.
  
  
  METHODS
  Eighty disk-shaped specimens were prepared using a split Teflon mold (6 × 2 mm) and were irradiated with either the QTH (Elipar 2500; 600 mW/cm(2)) for 20 seconds or an LED (Bluephase G2; 1,200 mW/cm(2)) for 40 seconds. The microhardness values were recorded using a Vickers hardness tester at a 300 g load for 15 seconds, immediately after polymerization, after 24 hours, and after three months of dark aging in distilled water at 37°C. Statistical analysis was performed using a two-way analysis of variance (ANOVA) and the Tukey's test.
  
  
  RESULTS
  The baseline values demonstrated a significant effect of the composite and the interaction composite-LCU on the microhardness (P < 0.05). At 24 hours, only the composite variable showed a significant effect on the hardness values (P < 0.05). After three months, the composite, LCU, and the interaction composite-LCU all demonstrated a significant effect on the microhardness (P < 0.05).
  
  
  CONCLUSIONS
  The effectiveness of polymerization, measured in terms of surface hardness, was shown to be dependent not only on the type of light curing unit, but also on the type of composite. Moreover, the choice of composite was shown to affect the performance of the light curing unit.
authors.affiliation: Department of Restorative Dentistry, School of Dental Medicine, SUNY at Buffalo, Buffalo, NY, USA.
authors.forename: Camila
authors.initials: C
authors.lastname: Sabatini
keywords: Composite resin; halogen; light-emitting diodes; microhardness; polymerization