Effect of modulated irradiation time on the degree of conversion and the amount of elutable substances from nano-hybrid resin-based composites

Abstract

The aim of our study was to analyse whether the irradiation time and/or the modulation of irradiation time influence the degree of conversion (DC) and the amount of elutable substances from modern nano-hybrid resin-based composites (RBCs). The DC was recorded in real time for 5min by means of attenuated total reflectance-Fourier transform infrared spectroscopy (n = 5) on the lower surface of 2-mm-thick samples irradiated with continuous and modulated irradiation times for 20s and 40s. The modulated times comprise a short polymerisation (2s or 5s) followed by a rest period of 1min and an additional polymerisation to complete 20s and 40s of polymerisation (2s + 18s, 5s + 15s, 2s + 38s and 5s + 35s). After storing the specimens in ethanol/water for 7days at 37°C, the eluates were analysed by gas chromatography-mass spectrometry. Results were statistically analyzed using a one-way ANOVA analysis (α = 0.05). The effect of irradiation time on DC is similar in all three analyzed materials, showing a significant increase in DC by increasing irradiation time from 20s to 40s, while the DC is not influenced within one irradiation time (20s or 40s) by the modulation of time. The type and amount of eluates are strongly dependent from the material and the irradiation protocol. An interrupt irradiation of RBCs is clinically feasible, reducing in general the amount of elutable substances at similar DC as the corresponding continuous polymerisation.