Abstract This paper evaluated the influence of the incorporation of the coinitiator Ethyl 4-(dimethylamino) benzoate (EDB) in Filtek Z250 XT resin in the reduction of the polymerization time and its behavior in halogen light and LED (Light Emitting Diode) light. The samples were subjected to thermal and spectroscopic analysis. The TG/DTG-DTA curve showed that both samples studied have a thermal stability temperature similar to the other polymers in the monomer blend. Morphological features were analyzed by SEM. By the MIR analysis, the degree of conversion using halogen light showed a better result compared to the LED light. The polymerization time applied to the specimens was 10 seconds, reducing the original resin time by half.