Comparative analysis of conversion and crosslinking degree in bulk-fill, monochromatic, and ORMOCER composites

Bulk-fill, monochromatic, and ORMOCER composites were introduced in restorative dentistry with the aim of reducing clinical time and/or alleviating contraction stresses at the interface between the tooth and restoration. While the conversion and immediate properties of these materials are comparable to conventional composites, studies evaluating their long-term properties and the structure of the polymer matrix are lacking. The objective of this study was to evaluate the degree of conversion and, indirectly, the crosslink density of conventional, bulk-fill, monochromatic, and ORMOCER resin composites. The degree of conversion was measured using Fourier-transform infrared spectroscopy (FTIR). Flexural strength, elastic modulus, and hardness were measured both dry (24 h) and after ethanol storage (24 h) using three-point bending and Knoop microhardness testing, respectively. Sorption and solubility were determined by changes in mass before and after immersion in water and drying. Data were analyzed using one-way or two-way ANOVA (material or material/storage conditions). The degree of conversion was statistically similar across all materials. For composites from the same manufacturer, no significant differences were observed in the reduction of mechanical properties after ethanol storage between bulk-fill and monochromatic composites, although differences were noted for the ORMOCER material. Sorption and solubility varied among most composites from the same manufacturer, suggesting subtle differences in composition. Therefore, it can be concluded that, for composites from the same manufacturer, the degree of crosslinking was similar between bulk-fill and monochromatic composites, indicating comparable polymeric structures. The same was not observed for the ORMOCER material, although it exhibits properties similar to other conventional composites.