Examination of degree of conversion, water sorption and solubility values of a bulk fill composite polymerized with different tilt angles

Objective: The aim of this study was to investigate the possible effects of a bulk-fill composite prepared with different slopes on the degree of conversion, water absorption, and water-solubility properties of the material in vitro after polymerization with two light-curing units at different distances. Method: A bulk-fill composite resin (Filtek Bulk Fill) placed in cylindrical teflon molds with 4 mm depth, angled at different degrees cured (90°, 75°, 60°, 45°), with two different LED light-curing units (VALO Cordless, iLed Curing Ligt). Curing was performed at three different distances (0 mm, 2 mm, 4 mm). A total of 24 groups were prepared with 5 samples in each group. The degrees of conversion of the samples were measured with the Fourier Transform Infrared Spectrometer device. After the composites were kept in distilled water at 37±1°C for 21 days, water absorption and water solubility values were calculated according to ISO 4049:2009 specification. Three-way Analysis of Variance and Duncan's multiple comparison test were used in the statistical analysis of the degree of conversion data. Water absorption and water solubility results were investigated by the Kruskal-Wallis test. Results: Among all samples, the highest mean degree of conversion value (41.55%±4.38%) was obtained in the group where the VALO light-curing unit was applied from the closest distance to the samples prepared with 90° angulation of the polymerization process. The lowest mean degree of conversion value (8.97±4.59%) was obtained in the group where the iLED light-curing unit was applied to the samples prepared with an angulation of 45°, from a distance of 4 mm. It was detected that the conversion degrees of the samples were affected by the type of light-curing unit used (p=0.003), the distance of light-curing unit (p=0.002), and the slope design of the prepared samples (p<0.001). In addition, it was noticed that the VALO light-curing unit showed more successful results on the transformation degrees of bulk-fill composite samples with different inclination angles (p<0.034). There was no statistically significant difference between the water absorption values of the bulk-fill composite resin samples polymerized under different conditions (p=0.585). Likewise, there was no statistically significant difference between the water solubility values of the samples (p=0.654). Conclusion: Although bulk-fill composite resins provide time savings and ease of application, they should be used carefully in clinical use, especially in deep and inclined cavities, considering the possibility of insufficient light energy reaching the material.