Thermal Changes and Degree of Conversion Using a blue LED

Thermal changes and degree of conversion of composite resins can be influenced by the parameters used during the photo-activation process. Objectives: The aim of this study was to investigate the TC (°C) and DC (%) of a microhybrid composite resin light-cured with a second generation blue LED. Methods: For the TC (°C), the samples were made in a metallic mould (2mm thickness and 4mm diameter) and light-cured during 20 s. The thermocouple was attached to the multimeter to allow the temperature readings. For the KBr pellet technique, the composite resin was placed into a metallic mould (1mm thickness and 4mm diameter) and light-cured with different power density values (400–1000 mW/cm2). The measurements for the DC (%) were made in a FTIR Spectrometer Bomen (model MB-102, Quebec–Canada). The spectroscopy (FTIR) spectra for both uncured and cured samples were analyzed using an accessory for the diffuse reflectance. The measurements were recorded in the absorbance operating under the following conditions: 32 scans, 4cm–1 resolution, and a 300 to 4000 cm–1 wavelength. The percentage of unreacted carbon–carbon double bonds (% C=C) was determined from the ratio of the 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). The TC (°C) and DC (%) were calculated by the standard technique and submitted to ANOVA and Tukey's test (p<0.05). Results: For the TC (°C), the values ranged from 9.3 (±0.19) to 15.0 (±0.95) for 20 s. The degree of conversion values varied from 52.0 (±2.0) to 53.0 (±2.4) for 20 s. Conclusion: The power densities showed a significant effect on temperature changes and on degree of conversion produce a saturated DC (%) mean values since 400 mW/cm2.