effect of shade and light curing mode on the degree of conversion of silorane-based and methacrylate-based resin composites

statement of problem: the degree of conversion depends on the material composition, light source properties, distance from light source, light intensity, curing time, and other factors such as shade and translucency. objectives: in the present study, we evaluated the effects of different light- curing modes and shades of methacrylate and silorane-based resin composites on the degree of conversion of resin composites (dc). materials and methods: the methacrylate-based (filtek z250, 3m, espe) and low-shrinkage silorane-based (filtek p90, 3m, espe) resin composites were used in three groups as follows: group 1-filtek z250 (shade a3), group 2-filtek z250 (shade b2), and group 3-filtek p90 (shade a3). we used a light-emitting diode (led) curing unit for photopolymerization. 10 samples were prepared in each group to evaluate the degree of conversion; 5 samples were cured using soft-start curing mode, and the other 5 were cured using standard curing mode. the dc of the resin composites was measured using fourier transform infrared spectroscopy (ftir). the data were analyzed using kruskal wallis and one- way anova statistical tests. results: the degree of conversion of silorane-based resin composite was 70 - 75.8% and that of methacrylate-based resin composites was 60.2 - 68.2% ( p = 0.009). the degree of conversion of the composite with brighter colour (b2) was statistically more than the darker composite (a3). higher degree of conversion was achieved applying the standard curing mode. conclusions: the results of the study showed that the colour and type of the resin composite and also the curing mode influence the degree of conversion of resin composites.