The effect of light curing source on the residual yellowing of resin composites

Purpose. This study evaluated the amount of residual yellow in cured resin composites when polymerizing with either a quartz-tungsten-halogen (QTH) or blue light-emitting diode (LED). Material and Methods: Twelve shades (bleaching to conventional shades) of microfill, hybrid and microhybrid resin composite specimens (n=10) were polymerized with both light types. All the materials contained only camphorquinone as the photoinitiator. After exposure, the specimens were stored in the dark for 24 hours. Then, the specimen color parameters were recorded (L*, a*, b* and C* _ab) and color differences (ΔE*_ab) were determined by examining for changes among the test combinations. Group comparisons were examined using ANOVA and the Tukey-Kramer post-hoc test, and pairwise comparisons were made using the Student's t-tests at a pre-set alpha of 0.05. Results: When a significant difference in the shade of yellow was noted, the QTH light produced a greater yellow tinge than most comparisons using the LED. The potential for producing more residual yellowing could not be anticipated with respect to composite filler classification or shade, as this effect may be more dependent on individual product composition. The extent to which residual yellowing differences were noted between light curing units fell within levels considered detectable by the human eye (ΔE>2.0). Conclusion: The selection of light curing unit to polymerize resin-based restorative materials can have a significant influence on the amount of residual yellow present, with the QTH light tending to leave more yellow than an LED unit.