Effect of LEDs Exposure Time on Curing Depth of Composite

Objectives: The aim of this study was to evaluate the extent of cure as a function of the light curing unit and exposure time. Methods: Samples were prepared using a microhybrid resin composite (Charisma/Kulzer) in a cylindrical steel matrix with 4 mm diameter and 5mm depth. Cure values were measured at simulated lighting conditions 1.0, 2.0 and 3.0mm below the top using Vickers Hardness Test. Three light-curing units were used: two LEDs (1) Elipar Free Light /3M-ESPE and (2) Ultraled/Dabi Atlante) and a halogen unit (3) XL 3000/3M). For all light units, five specimens were light-cured for 40s. Additional specimens were prepared and light-cured for 20s with light units 1 and 3. All light-exposed specimens were placed in the dark for a period of 24h at 37 ± 2oC. The Vickers Test (Hmv-2 Series Shimatzur Corporation) was carried out using a load of 300g for 15s and six indentations were made for each depth. The microhardness values were statistically analyzed by ANOVA and Tukey at a significance level of p<0.05. Results: For all depths, there were no differences between curing units when the 20s exposure time was used. The 40s light exposure time produced greater hardness values than 20s. For all curing units and exposure times, the microhardness depth ranked: 3 < 2 < 1mm. The Halogen light unit presented greater hardness values than the other two light units after 40s of exposure. Conclusions: The results allow to conclude that the curing of the composite was not adequate at depths greater than 2mm and that the halogen light unit produces greater microhardness than LEDs curing unit.