Relative performance of light emitting diode photo-polymerization units

Objectives: The aim of this study was to assess the effectiveness of several new Light Emitting Diode (LED) curing light sources delivering a high output, and compare them with a conventional (QTH) and a high intensity (HQTH) tungsten quartz halogen light with respect to depth of cure and microhardness. Methods: Ten LED and two halogen light curing units were evaluated. A hybrid composite resin (Filtek Z250 A3 shade) was placed into one half of a split cylindrical aluminum mold and photo polymerized using continuous light photo activation with each light source for 40 seconds. Ten samples were prepared for each light source. The cure depth was determined using a standard technique (ISO 4049:2000) and Vickers hardness values determined at 1.0 mm intervals along the length of the cured sample. Data were evaluated using analysis of variance (ANOVA) and Student's t test. Results: The maximum depth of cure was obtained with the G Light (3.09mm) and the minimum depth of cure obtained with the QTH Curing Light 2500 (2.76mm). All LED lights produced a significant increase in depth of cure when compared with conventional QTH and many when compared with the HQTH light. Vickers hardness values produced by LEDs and HQTH lights at 0mm,1mm and 2mm intervals were significantly greater than the conventional QTH (p<0.05). All light sources could produce hardness values greater than 80% of the top surface hardness when measured 2mm below the surface. The Pen Cure and LEDemetron 2 were the only light sources that could produce 80% of the surface hardness at the 3mm interval. Conclusion: This study demonstrated that the new LED curing lights are at least as effective as the high intensity quartz tungsten halogen lights in polymerization of composite resin and some appear to provide improvements in resin polymerization.