# Effect of the Silanization of Aerosil OX50 in the Properties of Light-Cured Dental Composites
## 4 Discussion
One way to explain this change is that the appropriate modification of the surface of a nanoparticle by a silane coupling agent involves the removal of the hydroxyl groups present on its surface together with the formation of new siloxane bonds (-Si-O-Si) between them. This new interaction causes the alteration in the agglomerates of the nanoparticles before and after the silanization process. In addition, during the development of this process, the first reaction that occurs is the hydrolysis of the alkoxy groups of the silane molecule that become silanol groups (-Si-OH) and, when this occurs, the silane molecules can react with each other and form dimers or oligomers. Light-cured composite resins have the advantage of being systems with unlimited working time before the material cures. However, the efficiency in polymerization is of prime importance in their behavior. The degree of conversion indicates the percentage of double bonds that have been converted into single bonds, that is, the number of monomers in the resin that have reacted to form polymers and can be determined by FTIR. In Figure 5a, it can be seen how the band corresponding to the vibrations of the aliphatic C=C double bonds decreases in intensity as the irradiation time increases, which demonstrates the progress of the polymerization process. Properties such as compressive and diametric compression strength, elastic modulus, as well as color stability, solubility, and cytotoxicity, are closely related to the conversion. A low degree of conversion favors the presence of residual monomer inside the cavity, which can be toxic to the pulp, demonstrating that this property is closely related to the biocompatibility of composite resins. For these materials, the conversion from monomer to polymer occurs from 55-75% [28]. The nature of the monomers that make up the monomeric matrix, the filler content, the intensity of the irradiated light, and the irradiation time are aspects of great influence on this property. As can be seen in Figure 5b, in all cases there is a sudden increase in the degree of conversion early in irradiation. Then, this increase becomes less pronounced until 5 s of polymerization, from which time until 80 s the value of the property does not change appreciably, a factor that is due to the decrease in active centers (free radicals) and to their low mobility when the viscosity increases with the occurrence of the polymerization reaction. The results obtained for the degree of conversion (Table 2) are totally satisfactory, as they give a measure of the lower toxicity that they can present if we compare them with the commercial composites in the literature. The higher DC values in matrices M1 and M4 are because the monomeric mixtures do not contain filler. It is known that the inorganic filler influences this property, since it increases the viscosity of the composite and hinders the diffusion of light emitted during irradiation and in some cases also the mobility of the organic molecules. The composites obtained have a degree of conversion between 65% and 85%, which is higher than those reported in other studies, as in the case of [PERSON] et al. in 2023 [29]. They evaluated the degree of conversion of different dental resins containing nanofhybrid silica derived from rice husk as inorganic filler (40, 50, and 60% by weight). For these composites, they obtained conversion values from 60-65%. The result of the statistical test for the degree of conversion shows that there are significant differences between the formulated materials. To determine which composite materials present significant differences among themselves, a multiple comparison test was performed. This showed that there are no significant differences between the degree of conversion of the Bis-GMA/TEEGDMA/MPS (M1) and Bis-GMA/TEEGDMA (M4) monomeric matrices and between the composites prepared with M4 (C445 and C445s).