The Effect of Different Resin Composite Thicknesses and Irradiation Times on the Degree of Conversion of Two Bulk-Fill Resin Composites

To evaluate the effect of resin thickness, and irradiation time on the degree of conversion of two bulk-fill resin composites; Tetric EvoCeram, and X-tra Fil. 120 cylindrical specimens were prepared, and divided into 24 groups (n=5/group), representing the two bulk-fill resin composites, three different material thicknesses (2, 3 and 4mm) and the four irradiation times used in the study (10, 20, 40, and 60 seconds). The specimens were light-cured from the top surface only. Specimens were stored in light proof containers in complete darkness at 37 degrees C for 24 hours. Degree of conversion test was conducted using FT-IR analysis. Data were statistically analyzed by Three-way ANOVA of Variance. Three-way ANOVA showed that different tested materials, thicknesses and irradiation times had a statistically significant effect on mean degree of conversion % at p=0.001. The highest mean degree of conversion value was recorded for X-tra Fil 2mm thickness group light-irradiated for 60 seconds (97 +/-0.17%), while the lowest value was recorded for X-tra Fil 4mm thickness group light-irradiated for 10 seconds (80.71 +/-0.25%). A 10 seconds irradiation time was enough to reach an acceptable degree of conversion for both tested bulk-fill resin composites when placed in 4mm bulks as recommended by their manufacturers. The resin chemistry seems to positively influence the polymerization process in the two tested bulk fill resin composite materials.