The purpose of this study was to investigate the amount of residual monomer in a composite resin after light-curing with different sources, light intensities and spectra of radiation. The resin specimens (4 mm in diameter; 2 mm thick) (n=5) were inserted in Plexglass matrixes and light-cured with a halogen lamp, LED and PAC units for 40, 40 and 5 s, respectively. The polymerized specimens were ground and 25 mg of each specimen were immersed in 8 mL 96% ethanol for 24 h to extract the residual

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... nomer. The amount of residual monomer was determined by the standard straight line method. The light spectrum of the different LCUs was shot and processed through researches of the absorbation of the standard solutions at a level of lambda= 275 nm and their extracts. Data were analyzed statistically by variational dispersion analysis and Tukey-Kramer test at 5% significance level. It was observed that, the halogen lamp produced the smallest amount of monomer under sufficient light intensity. The spectrum of light radiation of PAC was within the limits of 450- 490 nm and was of extremely high intensity. This imposes the use of short-limited light impulses, but also might lead to deterioration quality of polymerization. The LED unit had the best spectral radiation. An increase of light intensity was proved necessary.