Degree of conversion and temperature increase of a composite resin light cured with an argon laser and blue LED

Different light sources and power densities used on the photoactivation process may provide changes in the degree of conversion (DC%) and temperature (T) of the composite resins. Thus, the purpose of this study was to evaluate the DC (%) and T (°C) of the microhybrid composite resin (Filtek™ Z-250, 3M/ESPE) photoactivated with one argon laser and one LED (light-emitting diode) with different power densities. For the KBr pellet technique, the composite resin was placed into a metallic mould (2-mm thickness, 4-mm diameter) and photoactivated as follows: a continuous argon laser (CW) and LED LCUs with power density values of 100, 400, 700, and 1000 mW/cm2 for 20 s. The measurements for DC (%) were made in a FTIR spectrometer Bomen (model MB 102, Quebec, Canada). Spectroscopy (FTIR) spectra for both uncured and cured samples were analyzed using an accessory of the reflectance diffusion. The measurements were recorded in absorbance operating under the following conditions: 32 scans, 4 cm−1 resolution, 300 to 4000-cm−1 wavelength. The percentage of unreacted carbon double bonds (% C=C) was determined from the ratio of absorbance intensities of aliphatic C=C (peak at 1638 cm−1) against an internal standard before and after the curing of the specimen: aromatic C-C (peak at 1608 cm−1). For T (°C), the samples were created in a metallic mould (2-mm thickness, 4-mm diameter) and photoactivated for 20 s. The thermocouple was attached to the multimeter allowing temperature readings. The DC (%) and T (°C) were submitted to ANOVA and Tukey’s test (p < 0.05). The degree of conversion values varied from 35.0 to 50.0% (100 to 1000 mW/cm2) for an argon laser and from 41.0 to 49% (100 to 1000 mW/cm2) for an LED. The temperature change values varied from 1.1 to 13.1 °C (100 to 1000 mW/cm2) for an argon laser and from 1.9 to 15.0 °C (100 to 1000 mW/cm2) for an LED. The power densities showed a significant effect on the degree of conversion and changes the temperature for both lightcuring units.